Genomic characterization of New Delhi metallo-beta-lactamase-producing species of Morganellaceae, Yersiniaceae, and Enterobacteriaceae (other than Klebsiella) from Brazil over 2013-2022

Over the last decade, New Delhi metallo-beta-lactamase (NDM) carbapenemase has silently spread in Brazil. In this study, we analyzed a large collection of Enterobacterales other than Klebsiella spp. received in our reference laboratory between 2013 and 2022. A total of 32 clinical isolates displaying different pulsed-field gel electrophoresis profiles, and represented by 11 species in the families Enterobacteriaceae (Citrobacter freundii, Citrobacter portucalensis, Enterobacter hormaechei, and Escherichia coli), Morganellaceae (Morganella morganii, Proteus mirabilis, Proteus vulgaris, Providencia rettgeri, Providencia stuartii, and Raoultella ornithinolytica), and Yersiniaceae (Serratia marcescens) had their whole genomes sequenced and further analyzed. Antimicrobial susceptibility was determined by disk diffusion, except for polymyxin B, assessed by broth microdilution. The blaNDM-1 allele was predominant (n = 29), but blaNDM-5 was identified in an E. coli specimen with a novel ST, and the blaNDM-7 allele was found in E. hormaechei ST45 and E. coli ST1049. Polymyxin was active against all but one Enterobacteriaceae isolate: an mcr-1-producing E. coli presenting minimal inhibitory concentration (4 mg/L). Isolates producing extended-spectrum β-lactamases were common: cefotaximase from Munich (CTX-M)-15 (n = 10), CTX-M-2 (n = 4), and CTX-M-8 (n = 3) were detected, and the mcr-1-producing E. coli was found to co-produce both CTX-M-8 and CTX-M-55 β-lactamases. The mcr-9 gene was found in 5/8 E. hormaechei isolates, distributed in four different sequence types, all of them presenting susceptibility to polymyxin. This study showed that NDM-producing Enterobacterales other than Klebsiella are already spread in Brazil, in diversified species, and cocarrying important resistance genes. Prompt detection and effective implementation of measures to prevent further spread are mandatory for mitigating the dissemination of NDM carbapenemase in hospital settings and preserving the already limited antimicrobial therapy options.

Emergence of colistin-resistant Enterobacter cloacae and Raoultella ornithinolytica carrying the phosphoethanolamine transferase gene, mcr-9, derived from vegetables in Japan

IMPORTANCE

Plasmid-mediated mobile colistin-resistance genes have been recognized as a global threat because they jeopardize the efficacy of colistin in therapeutic practice. Here, we described the genetic features of two mcr-9.1-carrying Gram-negative bacteria with a colistin-resistant phenotype derived from vegetables in Japan. The colistin-resistant mcr-9.1, which has never been detected in vegetables, was located on a large plasmid in Enterobacter cloacae CST17-2 and Raoultella ornithinolytica CST129-1, suggesting a high chance of horizontal gene transfer. To the best of our knowledge, this is the first report of mcr-9 in R. ornithinolytica. This study indicates that fresh vegetables might be a potential source for the transmission of mcr-9 genes encoding resistance to frontline (colistin) and clinically relevant antimicrobials. The study also provides additional consideration for colistin use and the relevance of routine surveillance in epidemiological perspective to curb the continuous spread of mcr alleles.

Surface water in Lower Saxony: A reservoir for multidrug-resistant Enterobacterales

The emergence of extended-spectrum β-lactamase and carbapenemase-producing Enterobacterales (ESBL-E and CPE, respectively) is a threat to modern medicine, as infections become increasingly difficult to treat. These bacteria have been detected in aquatic environments, which raises concerns about the potential spread of antibiotic resistance through water. Therefore, we investigated the occurrence of ESBL-E and CPE in surface water in Lower Saxony, Germany, using phenotypic and genotypic methods. Water samples were collected from two rivers, five water canals near farms, and 18 swimming lakes. ESBL-E and CPE were isolated from these samples using filters and selective agars. All isolates were analyzed by whole genome sequencing. Multidrug-resistant Enterobacterales were detected in 4/25 (16%) water bodies, including 1/2 rivers, 2/5 water canals and 1/18 lakes. Among all samples, isolates belonging to five different species/species complexes were detected: Escherichia coli (n = 10), Enterobacter cloacae complex (n = 4), Citrobacter freundii (n = 3), Citrobacter braakii (n = 2), and Klebsiella pneumoniae (n = 2). Of the 21 isolates, 13 (62%) were resistant at least to 3rd generation cephalosporins and eight (38%) additionally to carbapenems. CPE isolates harbored blaKPC-2 (n = 5), blaKPC-2 and blaVIM-1 (n = 2), or blaOXA-181 (n = 1); additionally, mcr-9 was detected in one isolate. Two out of eight CPE isolates were resistant to cefiderocol and two to colistin. Resistance to 3rd generation cephalosporins was mediated by ESBL (n = 10) or AmpC (n = 3). The presence of AmpC-producing Enterobacterales, ESBL-E and CPE in northern German surface water samples is alarming and highlights the importance of aquatic environments as a potential source of MDR bacteria.

Plasmid-encoded lactose metabolism and mobilized colistin resistance (mcr-9) genes in Salmonella enterica serovars isolated from dairy facilities in the 1980s

Horizontal gene transfer by plasmids can confer metabolic capabilities that expand a host cell's niche. Yet, it is less understood whether the coalescence of specialized catabolic functions, antibiotic resistances and metal resistances on plasmids provides synergistic benefits. In this study, we report whole-genome assembly and phenotypic analysis of five Salmonella enterica strains isolated in the 1980s from milk powder in Munich, Germany. All strains exhibited the unusual phenotype of lactose-fermentation and encoded either of two variants of the lac operon. Surprisingly, all strains encoded the mobilized colistin resistance gene 9 (mcr-9), long before the first report of this gene in the literature. In two cases, the mcr-9 gene and the lac locus were linked within a large gene island that formed an IncHI2A-type plasmid in one strain but was chromosomally integrated in the other strain. In two other strains, the mcr-9 gene was found on a large IncHI1B/IncP-type plasmid, whereas the lac locus was encoded on a separate chromosomally integrated plasmidic island. The mcr-9 sequences were identical and genomic contexts could not explain the wide range of colistin resistances exhibited by the Salmonella strains. Nucleotide variants did explain phenotypic differences in motility and exopolysaccharide production. The observed linkage of mcr-9 to lactose metabolism, an array of heavy-metal detoxification systems, and other antibiotic resistance genes may reflect a coalescence of specialized phenotypes that improve the spread of colistin resistance in dairy facilities, much earlier than previously suspected.

The role of the plasmid-mediated fluoroquinolone resistance genes as resistance mechanisms in pediatric infections due to Enterobacterales

Introduction

Fluoroquinolones (FQs) are not commonly prescribed in children, yet the increasing incidence of multidrug-resistant (MDR) Enterobacterales (Ent) infections in this population often reveals FQ resistance. We sought to define the role of FQ resistance in the epidemiology of MDR Ent in children, with an overall goal to devise treatment and prevention strategies.

Methods

A case-control study of children (0-18 years) at three Chicago hospitals was performed. Cases had infections by FQ-susceptible, β-lactamase-producing (bla) Ent harboring a non- or low-level expression of PMFQR genes (PMFQS Ent). Controls had FQR infections due to bla Ent with expressed PMFQR genes (PMFQR Ent). We sought bla genes by PCR or DNA (BD Max Check-Points assay®) and PMFQR genes by PCR. We performed rep-PCR, MLST, and E. coli phylogenetic grouping. Whole genome sequencing was additionally performed on PMFQS Ent positive isolates. Demographics, comorbidities, and device, antibiotic, and healthcare exposures were evaluated. Predictors of infection were assessed.

Results

Of 170 β-lactamase-producing Ent isolates, 85 (50%) were FQS; 23 (27%) had PMFQR genes (PMFQS cases). Eighty-five (50%) were FQR; 53 (62%) had PMFQR genes (PMFQR controls). The median age for children with PMFQS Ent and PMFQR Ent was 4.3 and 6.2 years, respectively (p = NS). Of 23 PMFQS Ent, 56% were Klebsiella spp., and of 53 PMFQR Ent, 76% were E. coli. The most common bla and PMFQR genes detected in PMFQS Ent were bla SHV ESBL (44%) and oqxAB (57%), and the corresponding genes detected in PMFQR Ent were bla CTX-M-1-group ESBL (79%) and aac(6')-Ib-cr (83%). Whole genome sequencing of PMFQS Ent revealed the additional presence of mcr-9, a transferable polymyxin resistance gene, in 47% of isolates, along with multiple plasmids and mobile genetic elements propagating drug resistance. Multivariable regression analysis showed that children with PMFQS Ent infections were more likely to have hospital onset infection (OR 5.7, 95% CI 1.6-22) and isolates containing multiple bla genes (OR 3.8, 95% CI 1.1-14.5). The presence of invasive devices mediated the effects of healthcare setting in the final model. Differences in demographics, comorbidities, or antibiotic use were not found.

Conclusions

Paradoxically, PMFQS Ent infections were often hospital onset and PMFQR Ent infections were community onset. PMFQS Ent commonly co-harbored multiple bla and PMFQR genes, and additional silent, yet transferrable antibiotic resistance genes such as mcr-9, affecting therapeutic options and suggesting the need to address infection prevention strategies to control spread. Control of PMFQS Ent infections will require validating community and healthcare-based sources and risk factors associated with acquisition.

Emergence of carbapenem-resistant Enterobacter hormaechei ST93 plasmids co-harbouring blaNDM-1, blaKPC-2, and mcr-9 in bloodstream infection

OBJECTIVES

We isolated a strain of Enterobacter hormaechei, ECC2783, co-harbouring blaNDM-1, blaKPC-2 and mcr-9 plasmids from a bloodstream infection and investigated its biological features.

METHODS

The presence of carbapenemase genes and mcr-9 was confirmed by polymerase chain reaction amplification. Whole genome sequencing and genomic analysis were performed on ECC2783. Experiments assessing the conjugation and stability of plasmids carrying the carbapenemase gene were performed. We also performed a colistin resistance induction experiment and studied the fitness cost of transconjugants.

RESULTS

ECC2783 has an extensive drug resistance phenotype. Multilocus sequence typing analysis results showed that ECC2783 belongs to sequence type 93. Bioinformatics analysis confirmed that ECC2783 has four plasmids, of which pECC2783_a, carrying mcr-9, is the IncHI2 type, and pECC2783_c, carrying blaNDM-1, is the IncX3 type. pECC2783_d, carrying blaKPC-2, is an unclassified type. We successfully obtained two transconjugants (J53/ECC2783_1, carrying blaNDM-1, and J53/ECC2783_2, carrying blaKPC-2 and blaNDM-1). There was no statistically significant difference in the relative growth rate between J53 and J53/ECC2783_2.

CONCLUSION

For the first time, we isolated carbapenem-resistant E. hormaechei plasmids co-harbouring blaNDM-1, blaKPC-2, and mcr-9 from a patient with a blood stream infection. This isolate has a survival advantage in a hospital environment, and its clinical monitoring should be strengthened.

First reported detection of the mobile colistin resistance genes, mcr-8 and mcr-9, in the Irish environment

The emergence and dissemination of mobile colistin resistance (mcr) genes across the globe poses a significant threat to public health, as colistin remains one of the last line treatment options for multi-drug resistant infections. Environmental samples (157 water and 157 wastewater) were collected in Ireland between 2018 and 2020. Samples collected were assessed for the presence of antimicrobial resistant bacteria using Brilliance ESBL, Brilliance CRE, mSuperCARBA and McConkey agar containing a ciprofloxacin disc. All water and integrated constructed wetland influent and effluent samples were filtered and enriched in buffered peptone water prior to culture, while wastewater samples were cultured directly. Isolates collected were identified via MALDI-TOF, were tested for susceptibility to 16 antimicrobials, including colistin, and subsequently underwent whole genome sequencing. Overall, eight mcr positive Enterobacterales (one mcr-8 and seven mcr-9) were recovered from six samples (freshwater (n = 2), healthcare facility wastewater (n = 2), wastewater treatment plant influent (n = 1) and integrated constructed wetland influent (piggery farm waste) (n = 1)). While the mcr-8 positive K. pneumoniae displayed resistance to colistin, all seven mcr-9 harbouring Enterobacterales remained susceptible. All isolates demonstrated multi-drug resistance and through whole genome sequencing analysis, were found to harbour a wide variety of antimicrobial resistance genes i.e., 30 ± 4.1 (10-61), including the carbapenemases, bla_OXA-48 (n = 2) and bla_NDM-1 (n = 1), which were harboured by three of the isolates. The mcr genes were located on IncHI2, IncFIIK and IncI1-like plasmids. The findings of this study highlight potential sources and reservoirs of mcr genes in the environment and illustrate the need for further research to gain a better understanding of the role the environment plays in the persistence and dissemination of antimicrobial resistance.

Draft genome sequences of rare Lelliottia nimipressuralis strain MEZLN61 and two Enterobacter kobei strains MEZEK193 and MEZEK194 carrying mobile colistin resistance gene mcr-9 isolated from wastewater in South Africa

OBJECTIVES

Antimicrobial-resistant bacteria of the order Enterobacterales are emerging threats to global public and animal health, leading to morbidity and mortality. The emergence of antimicrobial-resistant, livestock-associated pathogens is a great public health concern. The genera Enterobacter and Lelliottia are ubiquitous, facultatively anaerobic, motile, non-spore-forming, rod-shaped Gram-negative bacteria belonging to the Enterobacteriaceae family and include pathogens of public health importance. Here, we report the first draft genome sequences of a rare Lelliottia nimipressuralis strain MEZLN61 and two Enterobacter kobei strains MEZEK193 and MEZEK194 in Africa.

METHODS

The bacteria were isolated from environmental wastewater samples. Bacteria were cultured on nutrient agar, and the pure cultures were subjected to whole-genome sequencing. Genomic DNA was sequenced using an Illumina MiSeq platform. Generated reads were trimmed and subjected to de novo assembly. The assembled contigs were analysed for virulence genes, antimicrobial resistance genes, and extra-chromosomal plasmids, and multilocus sequence typing was performed. To compare the sequenced strains with other, previously sequenced E. kobei and L. nimipressuralis strains, available raw read sequences were downloaded, and all sequence files were treated identically to generate core genome bootstrapped maximum likelihood phylogenetic trees.

RESULTS

Whole-genome sequencing analyses identified strain MEZLN61 as L. nimipressuralis and strains MEZEK193 and MEZEK194 as E. kobei. MEZEK193 and MEZEK194 carried genes encoding resistance to fosfomycin (fosA), beta-lactam antibiotics (blaACT-9), and colistin (mcr-9). Additionally, MEZEK193 harboured nine different virulence genes, while MEZEK194 harboured eleven different virulence genes. The phenotypic analysis showed that L. nimipressuralis strain MEZLN61 was susceptible to colistin (2 μg/mL), while E. kobei MEZEK193 (64 μg/mL) and MEZEK194 (32 μg/mL) were resistant to colistin.

CONCLUSION

The genome sequences of strains L. nimipressuralis MEZLN6, E. kobei MEZEK193, and E. kobei MEZEK194 will serve as a reference point for molecular epidemiological studies of L. nimipressuralis and E. kobei in Africa. In addition, this study provides an in-depth analysis of the genomic structure and offers important information that helps clarify the pathogenesis and antimicrobial resistance of L. nimipressuralis and E. kobei. The detection of mcr-9, which is associated with very low-level colistin resistance in Enterobacter species, is alarming and may indicate the undetected dissemination of mcr genes in bacteria of the order Enterobacterales. Continuous monitoring and surveillance of the prevalence of mcr genes and their associated phenotypic changes in clinically important pathogens and environmentally associated bacteria is necessary to control and prevent the spread of colistin resistance.

Co-occurrence of blaNDM-1, rmtC, and mcr-9 in multidrug-resistant Enterobacter kobei strain isolated from an infant with urinary tract infection

OBJECTIVES

The co-emergence of mcr and carbapenem resistance genes in Gram-negative bacteria is a serious problem. This study aims to clarify the genetic characteristic of one novel multidrug-resistant Enterobacter kobei EC1382 with mcr-9 causing urinary tract inflammation in an infant.

METHODS

Antimicrobial drug susceptibility testing was performed for this isolate using the broth microdilution method. Whole-genome sequencing was performed using the Illumina PacBio RS II platform and HiSeq platform, and the antimicrobial resistance genes, mobile elements, and plasmid replicon types were identified. Conjugation analysis was performed using Escherichia coli C600 as recipients.

RESULTS

Enterobacter kobei EC1382 was resistant to carbapenem, aminoglycoside, and cephalosporin. Twenty-five antimicrobial resistance genes were identified, including genes conferring resistance to carbapenem (blaNDM-1), colistin (mcr-9), and aminoglycosides (rmtC). The blaNDM-1 gene, accompanied by bleMBL and rmtC located downstream of an ISCR14 element, was detected in the IncFII(Yp) type plasmid pEC1382-2. Interestingly, although E. kobei EC1382 was susceptible to colistin, it had three identical mcr-9 genes (two in the chromosome and one in the IncHI2-type plasmid pEC1382-1). The backbone (∼12.2-kb genetic fragment) of these mcr-9 (flanked by IS903B and IS481-IS26) regions were conserved in this strain, and they were found to be present in various bacteria as three types, implying a silent distribution.

CONCLUSIONS

To the best of our knowledge, this is the first study to demonstrate the coexistence of blaNDM-1, rmtC, and mcr-9 in E. kobei. The silent prevalence of mcr-9 in bacteria may be a threat to public health.

Host range of strand-biased circularizing integrative elements: a new class of mobile DNA elements nesting in Gammaproteobacteria

BACKGROUND

The strand-biased circularizing integrative elements (SEs) are putatively non-mobilizable integrative elements for transmitting antimicrobial resistance genes. The transposition mode and the prevalence of SEs in prokaryotes remain vague.

RESULTS

To corroborate the transposition mode and the prevalence of SEs, hypothetical transposition intermediates of an SE were searched for in genomic DNA fractions of an SE host. Then, the SE core genes were defined based on gene knockout experiments, and the synteny blocks of their distant homologs were searched for in the RefSeq complete genome sequence database using PSI-BLAST. A genomic DNA fractionation experiment revealed that SE copies are present in a double-stranded nicked circular form in vivo. Operonic structure of three conserved coding sequences (intA, tfp, intB) and srap located at the left end of SEs were identified as essential for attL × attR recombination. The synteny blocks of tfp and srap homologs were detected in 3.6% of the replicons of Gammaproteobacteria but not in other taxa, implying that SE movement is host-dependent. SEs have been discovered most frequently in the orders Vibrionales (19% of replicons), Pseudomonadales (18%), Alteromonadales (17%), and Aeromonadales (12%). Genomic comparisons revealed 35 new SE members with identifiable termini. SEs are present at 1 to 2 copies per replicon and have a median length of 15.7 kb. Three newly identified SE members carry antimicrobial resistance genes, like tmexCD-toprJ, mcr-9, and bla_GMA-1. Further experiments validated that three new SE members possess the strand-biased attL × attR recombination activity.

CONCLUSIONS

This study suggested that transposition intermediates of SEs are double-stranded circular DNA. The main hosts of SEs are a subset of free-living Gammaproteobacteria; this represents a rather narrow host range compared to those of mobile DNA element groups discovered to date. As the host range, genetic organization, and movements are unique among the mobile DNA elements, SEs provide a new model system for host-mobile DNA element coevolution studies.

Phenotypic and Genomic Characterization of ST133 Siderophore-Encoding Extensively Drug-Resistant Enterobacter hormaechei

We identified an ST133 extensively drug-resistant Enterobacter hormaechei, C210017, with increased virulence in the Galleria mellonella infection model. Genomic analysis suggested it carried antibiotic resistance genes bla_KPC-2 and mcr-9.1, and genes iutAiucABCD and iroBCDEN encoding the virulence factor, siderophores. Comparative genomics of C210017 and the 178 ST133 E. hormaechei strains in the database suggested they all belonged to serotype O3 and most strains (77.5%) carried the IncHI2 superplasmids associated with the resistance, virulence, and adaptation of the host strain.

Genomic characterization of ESBL-producing Salmonella Thompson isolates harboring mcr-9 from dead chick embryos in China

The emergence and dissemination of the extended spectrum β-lactamase (ESBL)-producing Enterobacteriaceae harbouring antimicrobial resistance (AMR) genes has diminished the potential options for treating multidrug-resistant (MDR) bacterial infections. Until now, numerous studies reported the spreading of critical plasmid-borne AMR genes from different sources worldwide. While the knowledge on the occurrence of the plasmid-borne AMR genes, especially mcr genes in the dead chick embryos, remains obscure. A retrospective study was conducted to detect the presence of the mcr genes in forty-five Salmonella enterica isolates recovered from 2139 dead chick embryo samples, from breeding chicken hatcheries in Henan, China. Using multiplex PCR, we found only four isolates out of the forty-five were mcr-9-positive. These four isolates were found to be MDR, ESBL- producing and showed resistance to 10 antimicrobial drugs. Additionally, mcr-9 harbouring plasmids were successfully transferred into Escherichia coli (E. coli) J53 by conjugation and the mcr-9 gene was confirmed by PCR. We also found that the transconjugants exhibited higher MICs for ampicillin, gentamycin and colistin than the recipient. Whole-genome sequence analysis showed that the four isolates belonged to Salmonella Thompson ST26 and harboured IncHI2 plasmid replicon. Furthermore, the mcr-9 harbouring plasmids were reconstructed using in silico tools and found to be carried other AMR genes (bla_DHA-1 and qnrB4). The studied isolates carried the typical virulence factors from Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2), in addition to pef and csg operons which are important in host adhesion and biofilm formation. The mgtC gene, which is involved in phagocytosis, has also been identified. Together, the increase in the phenotypic resistance of the transconjugants and the plasmid in silico reconstruction analysis confirmed that the corresponding resistance genes might be located together on the same plasmid. To track the potential phylogenomic relations of our detected ESBL S. Thompson isolates, we constructed a phylogenomic tree with available ESBL S. Thompson genomes (n = 26) that were reported worldwide. The studied isolates were independently clustered together with four other Chinese isolates of food origin in one clade, providing strong evidence of a potential recent and wide dissemination of ESBL S. Thompson across the food chain in China. In conclusion, we report the detection of four highly virulent ESBL-producing S. Thompson ST26 isolates harbouring mcr-9 gene obtained from dead chick embryos in Henan, China.

High-risk international clones ST66, ST171 and ST78 of Enterobacter cloacae complex causing blood stream infections in Spain and carrying blaOXA-48 with or without mcr-9

BACKGROUND

In the last years, Enterobacter cloacae complex has become an important threat associated with nosocomial infections (including bacteraemia). These bacteria have the ability to acquire mobile genetic elements with antimicrobial resistance genes, reducing the number of therapies available for treatment of the infections they cause. Multidrug resistant isolates of the E. cloacae complex have been causing blood stream infections in a hospital in northern Spain. The aim of this study was to report the spread of E. cloacae complex isolates carrying bla_OXA-48 with or without mcr-9 which were involved in blood stream infections, in a Spanish hospital.

METHODS

All Enterobacter spp. isolates recovered from blood cultures of patients admitted to a tertiary Spanish hospital, over a five-year period were recovered. Of those, OXA-48-producing isolates were selected for further analysis (19 E. xiangfangensis isolates and a single E. hoffmannii). Bacterial identification, antimicrobial susceptibility, DNA sequencing, molecular typing, resistome analysis and plasmid characterization was performed.

RESULTS

20 isolates were positive for bla_OXA-48, harbored by IncL/M plasmids. They belonged to the international high-risk clones ST66, ST171 and ST78. They produced the extended-spectrum β-lactamases CTX-M-15 and/or CTX-M-9 and 40 % of them (n = 8) also carried the mcr-9 gene, located on IncHI2 plasmids. However, they were susceptible to colistin.

CONCLUSION

The presence of bla_OXA-48, together with at least one bla_CTX-M gene in our multidrug resistant high-risk E. cloacae complex clones is worrisome. Also, the additional presence of mcr-9 in some of them is of concern as it could potentially be transferred into other hosts or acquire mutations that might led to emerging colistin resistance. Surveillance systems are essential to detect these difficult-to-treat bacteria which, apart from causing live-threatening infections, can spread important resistance threats.

First report of coexistence of bla KPC-2-, bla NDM-1- and mcr-9-carrying plasmids in a clinical carbapenem-resistant Enterobacter hormaechei isolate

Introduction

Colistin is regarded as one of the last-resort antibiotics against severe infections caused by carbapenem-resistant Enterobacteriaceae. Strains with cooccurrence of mcr-9 and carbapenemase genes are of particular concern. This study aimed to investigate the genetic characteristics of a bla _KPC-2-carrying plasmid, bla _NDM-1-carrying plasmid and mcr-9-carrying plasmid coexisting in a carbapenem-resistant Enterobacter hormaechei isolate.

Methods

E. hormaechei strain E1532 was subjected to whole-genome sequencing, and the complete nucleotide sequences of three resistance plasmids identified in the strain were compared with related plasmid sequences. The resistance phenotypes mediated by these plasmids were analyzed by plasmid transfer, carbapenemase activity and antimicrobial susceptibility testing.

Results

Whole-genome sequencing revealed that strain E1532 carries three different resistance plasmids, pE1532-KPC, pE1532-NDM and pE1532-MCR. pE1532-KPC harboring bla _KPC-2 and pE1532-NDM harboring bla _NDM-1 are highly identical to the IncR plasmid pHN84KPC and IncX3 plasmid pNDM-HN380, respectively. The mcr-9-carrying plasmid pE1532-MCR possesses a backbone highly similar to that of the IncHI2 plasmids R478 and p505108-MDR, though their accessory modules differ. These three coexisting plasmids carry a large number of resistance genes and contribute to high resistance to almost all antibiotics tested, except for amikacin, trimethoprim/sulfamethoxazole, tigecycline and polymyxin B. Most of the plasmid-mediated resistance genes are located in or flanked by various mobile genetic elements, facilitating horizontal transfer of antibiotic resistance genes.

Discussion

This is the first report of a single E. hormaechei isolate with coexistence of three resistance plasmids carrying mcr-9 and the two most common carbapenemase genes, bla _KPC-2 and bla _NDM-1. The prevalence and genetic features of these coexisting plasmids should be monitored to facilitate the establishment of effective strategies to control their further spread.

Epidemiology and Molecular Characteristics of mcr-9 in Citrobacter spp. from Healthy Individuals and Patients in China

With the globally prevailing carbapenemase-producing (CP) Citrobacter spp., polymyxin antibiotics have been reconsidered as one of the last-resort treatment options. Our study was conducted to investigate the prevalence of mcr-9 in Citrobacter species. From October to November 2021, 650 fecal samples and 215 Citrobacter isolates were collected from healthy individuals and infected patients, respectively. Isolates were screened for the presence of the mcr-9 gene by the PCR method. mcr-9-carrying strains were identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Due to the susceptibility to colistin, Citrobacter spp. isolates were first induced to increase the expression of mcr-9 on China blue agar plates containing colistin and were then subjected to conjugation experiments. Whole-genome sequencing was performed on the Illumina NovaSeq PE150 system. The prevalence of mcr-9 in the Citrobacter genus from healthy guts and infected patients was 0.62% and 1.86%, respectively. In all mcr-9-positive strains, MICs of polymyxin B were observed at ≤2 μg/mL, displaying a nonresistant phenotype. As for conjugation experiments, only one isolate successfully transferred the mcr-9 gene to Escherichia coli C600. Whole-genome sequencing showed that eight mcr-9-positive Citrobacter isolates carried mcr-9 and genes encoding resistance to beta-lactam antibiotics, including blaCMY, blaDHA, blaSHV, blaTEM, and blaCTX-M. We also discovered that mcr-9 could be located on the pKPC-CAV1321 plasmid. Our study investigated the prevalence of mcr-9 in Citrobacter spp. in both healthy individuals and infected patients and described the carriage of mcr-9 on the pKPC-CAV1321 plasmid for the first time. IMPORTANCE The emergence of mcr homologues posed a serious threat to the therapeutic efficiency of polymyxin antibiotics. Citrobacter freundii is generally regarded as an opportunistic pathogen associated with a variety of nosocomial infections. In this study, we investigated the prevalence of mcr-9 in Citrobacter spp. isolates from healthy individuals and infected patients and highlighted the importance of the rational use of antibiotics. In addition, this epidemiological investigation is the first to describe the carriage of mcr-9 on plasmid pKPC-CAV1321 and confirms the horizontal transfer of this plasmid. Our research may shed new light on further studies of mcr-9 dissemination in humans.

Modified Drug-Susceptibility Testing and Screening Culture Agar for Colistin-Susceptible Enterobacteriaceae Isolates Harboring a Mobilized Colistin Resistance Gene mcr-9

Three isolates of the Enterobacter cloacae complex harboring mcr-9, a member of the colistin resistance mcr gene family encoded on plasmids, were susceptible to colistin, with MICs of 0.125 to 0.5 μg/mL in standard broth microdilution (BMD) tests using cation-adjusted Mueller-Hinton broth (CA-MHB) in accordance with European Committee on Antimicrobial Susceptibility Testing guidelines. In contrast, their MICs for colistin were significantly higher (4 to 128 μg/mL) when BMD tests were performed using brain-heart infusion (BHI) medium, Luria-Bertani (LB) broth, tryptic soy broth (TSB), or CA-MHB supplemented with casein, tryptonen or peptone. Colistin significantly induced mcr-9 expression in a dose-dependent manner when these mcr-9-positive isolates were cultured in BHI or CA-MHB supplemented with peptone/casein. Pretreatment of mcr-9-positive isolates and Escherichia coli DH5α harboring mcr-9 with colistin significantly increased their survival rates against LL-37, a human antimicrobial peptide. Electrospray ionization time-of-flight mass spectrometry analysis showed that a lipid A moiety of lipopolysaccharide was partially modified by phosphoethanolamine in E. coli DH5α harboring mcr-9 when treated with colistin. Of 93 clinical isolates of Enterobacteriaceae, only the mcr-9-positive isolates showed MICs to colistin that were at least 32 times higher in BHI than in CA-MHB. These mcr-9-positive isolates grew on a modified BHI agar, MCR9-JU, containing 3 μg/mL colistin. These results suggest that the BMD method using BHI is useful when performed together with the BMD method using CA-MHB to detect mcr-9-positive isolates and that MCR9-JU agar is useful in screening for Enterobacteriaceae isolates harboring mcr-9 and other colistin-resistant isolates.

Molecular antibiotic resistance mechanisms and co-transmission of the mcr-9 and metallo-β-lactamase genes in carbapenem-resistant Enterobacter cloacae complex

Carbapenem-resistant Enterobacter cloacae complex (CRECC) has increasingly emerged as a major cause of healthcare-associated infections, with colistin being one of the last-resort antibiotics of treatment. Mobile colistin resistance (mcr)-9 is a member of a growing family of mcr genes and has been reported to be an inducible gene encoding an acquired phosphoethanolamine transferase. Here, we collected 24 ECC strains from Chongqing, China from 2018 to 2021. Subsequently, antibiotic resistance genes and the transmission dynamics of the strains were determined by PCR, whole-genome sequencing, and bioinformatic analysis. The mcr-9 was identified in IncHI2/2A or IncHI2/2A + IncN plasmids from six CRECC strains and was co-located with bla NDM-1 or bla IMP-4 in 2/6 plasmids. The genetic environment of mcr-9.1 was composed of IS903B-mcr-9.1-wbuC-IS26 in the five mcr-9.1-harboring-plasmid, but IS1B was located downstream of mcr-9.2 in the pECL414-1 sequence. We also found that the pNDM-068001 plasmid carrying mcr-9.1 could be a hybrid plasmid, formed by a Tn6360-like bla NDM-1 region inserted into an mcr-9.1-positive IncHI2/2A plasmid. A conjugation assay showed that plasmids mediated the co-dissemination of mcr-9 and metallo-β-lactamase (MBL) genes. In addition, we performed induction assays with sub-inhibitory concentrations of colistin and found an increase in the relative expression levels of the mcr-9.2, qseC, and qseB genes, as well as an increase in the minimum inhibitory concentration values of colistin in the CRECC414 strain. These findings provide a basis for studying the regulatory mechanisms of mcr-9 expression and highlight the importance of effective monitoring to assess the prevalence of MBL and mcr-9 co-existing plasmids.

Chromosomal coharboring of blaIMP-60 and mcr-9 in Enterobacter asburiae isolated from a Japanese woman with empyema: a case report

BACKGROUND

Polymyxin E (colistin) is a last-resort antibiotic to treat infections caused by carbapenemase-producing Enterobacteriaceae (CPE). However, reports of CPEs resistant to colistin have been increasing, and the mcr genes are emerging as resistance mechanisms. Among them, plasmid-mediate mcr-9 is known to be associated with colistin resistance, whereas reports on chromosomal mcr-9 and its association with colistin resistance in humans are few.

CASE PRESENTATION

We identified Enterobacter asburiae harboring mcr-9 and bla_IMP-60 in the pleural fluid of a patient with empyema. The long-read sequencing technique revealed that these genes were located on its chromosome. Despite the lack of exposure to colistin, the organism showed microcolonies in the inhibition circle in the E-test and disk diffusion test. Antibiotic susceptibility testing by broth microdilution confirmed its resistance to colistin.

CONCLUSION

Our case report showed that mcr-9 can be present not only on plasmids but also on the chromosome in E. asburiae, and that the presence of mcr-9 on its chromosome may influence its susceptibility to colistin.

Risk Factors for Community-Acquired Urinary Tract Infections Caused by Multidrug-Resistant Enterobacterales in Thailand

The dissemination of multidrug-resistant Enterobacterales (MDRE) in community settings is becoming a great concern. This study aimed to assess the incidence and risk factors associated with community-acquired urinary tract infections (CA-UTIs) caused by MDRE. A prospective case−control study was undertaken among patients with UTIs visiting an outpatient department in Phitsanulok Province, Thailand. Urine samples were collected and screened to include only patients with Enterobacterales infections. Risk factors were analyzed by multivariate logistic regression analysis. Of the 284 patients with CA-UTIs, 25.7% (n = 73) and 74.3% (n = 211) were positive for MDRE (case) and non-MDRE (control), respectively. Being a farmer was identified as an independent risk factor for MDRE-associated CA-UTIs (adjusted odds ratio = 3.101; 95% confidence interval = 1.272−7.564; p = 0.013). A total of 309 Enterobacterales isolates were recovered, and Escherichia coli was the most frequently detected (86.4%). The highest resistance rate was observed for ampicillin (67.0%), followed by ciprofloxacin (34.0%) and cotrimoxazole (32.7%), while resistance to third-generation cephalosporins (cefotaxime, ceftriaxone) and levofloxacin remained <20%. Resistance to ampicillin−gentamicin−cotrimoxazole was the most common pattern among MDRE isolates. Interestingly, we detected a colistin-resistant Enterobacter cloacae harboring mcr-9 (colistin MIC = 16 µg/mL). mcr-9 was transferable at high frequency (4.5 × 10−4) and resided on IncF plasmid. This study demonstrates that being a farmer is a risk factor for MDRE-associated CA-UTIs. Interestingly, this is the first report to identify mcr-9-positive E. cloacae from a Thai patient in the community.

Carriage of the mcr-9 and mcr-10 genes in clinical strains of the Enterobacter cloacae complex in China: a prevalence and molecular epidemiology study

OBJECTIVES

Enterobacter cloacae complex (ECC) is among the most common carbapenem-resistant Enterobacteriaceae in China. The emergence of the mcr renders CRE strains resistant to the last-line antibiotic colistin. We investigated the prevalence of mcr-9 and mcr-10 in carbapenem-resistant ECC (CRECC) and carbapenem-susceptible ECC (CSECC) in China.

METHODS

We collected CRECC and CSECC strains from different regions of China. The antimicrobial susceptibility tests, conjugation experiments, whole genome sequencing, bioinformatic analysis, and quantitative RT-PCR were performed to understand the mechanisms of resistance and transmission of mcr in ECC.

RESULTS

A total of 534 ECC were collected, among which 57 (10.7%) and 23 (4.3%) were positive for mcr-9 and mcr-10, respectively. The prevalence of mcr-9 in CRECC was significantly higher than that in CSECC (31.8% vs 3.7%, p < 0.001), while the prevalence of mcr-10 in CRECC was significantly lower (0.8% vs 5.5%, p < 0.05). Most mcr-9-positive strains (n=45, 78.9%) exhibited multidrug-resistant phenotype, and four (17.4%) of the mcr-10-positive strains exhibited multi-drug resistance. Coexistence of mcr and carbapenemase genes was commonly observed, including 41 (71.9%) mcr-9-positive strains and one (4.3%) mcr-10-positive strain, and the possibility of co-transfer was confirmed by conjugation experiments. The mcr-positive ECC were highly diverse, while most mcr genes were plasmid-encoded indicating the important role of plasmids on the transmission of mcr in ECC. Furthermore, the expression of mcr-9 was increased after induction by colistin.

CONCLUSIONS

The widespread of mcr genes, as well as its co-transfer with carbapenemase genes among ECC strains, posed an urgent threat to public health.

Frequent convergence of mcr-9 and carbapenemase genes in Enterobacter cloacae complex driven by epidemic plasmids and host incompatibility

Convergence of mcr and carbapenemase genes has been sporadically detected in Enterobacter cloacae complex (ECC) with an upward trend. However, the state of the epidemic and underlying mechanism of such convergence has been poorly understood. In this study, the co-occurrence of MCR and carbapenemases was systematically analyzed in 230 clinical ECC isolates collected between 2000 and 2018 together with a global dataset consisting of 3,559 ECC genomes compiled from GenBank. We identified 48 mcr-9/mcr-10-positive isolates (MCR-ECC) (20.9%) in our collection, and a comparable ratio of MCR-ECC (720/3559, 20.2%) was detected in the global dataset. A high prevalence of carbapenemase-producing MCR-ECC (MCR-CREC) was further identified in the MCR-ECC of both datasets (16/48, 33.3%; 388/720, 53.9%), demonstrating a frequent convergence of mcr-9/10 and carbapenemase genes in ECC worldwide. An epidemic IncHI2/2A plasmid with a highly conserved backbone was identified and largely contributed to the dissemination of mcr-9 in ECC worldwide. A highly conserved IncX3-type NDM-1-carrying plasmid and IncN-type IMP-4-carrying plasmid were additionally detected in MCR-CREC isolated in China. Our surveillance data showed that MCR-CREC emerged (in 2013) much later than MCR-ECC (in 2000), indicating that MCR-CREC could be derived from MCR-ECC by additional captures of carbapenemase-encoding plasmids. Tests of plasmid stability and incompatibility showed that the mcr-9/mcr-10-encoding plasmids with the NDM-1-encoding plasmids stably remained in ECC but incompatible in Escherichia coli, suggesting that the convergence was host-dependent. The findings extend our concern on the convergence of resistance to the last resort antibiotics and highlight the necessity of continued surveillance in the future.

Resistance and Pathogenicity of Salmonella Thompson Isolated from Incubation End of a Poultry Farm

Simple Summary

Non-typhoid Salmonella is the general term of Salmonella other than typhoid and paratyphoid, which often causes foodborne gastroenteritis in humans, but some serotypes have been proved to be pathogenic to poultry. Salmonella Enterica and Salmonella Typhimurium are the common serotypes pathogenic to poultry and have been systematically studied, but other serotypes have rarely been studied. During Salmonella surveillance in farms, we discovered by chance that Salmonella Thompson, a common non-typhoid Salmonella, is also pathogenic to avian embryos. Therefore, this study aimed to explore antimicrobial resistance and pathogenicity of clinical S. Thompson. Firstly, we found that the core-genome multilocus sequence typing of 14 clinical S. Thompson was consistent with two strains of S. Thompson from humans in China. Secondly, the antimicrobial resistance gene analysis demonstrated that all strains carried the polymyxin resistance gene mcr-9, which had not appeared resistance phenotype. Meanwhile, many essential virulence genes were also found in each S. Thompson isolate. Finally, the bacterial inoculation experiment revealed that clinical S. Thompson was highly pathogenic to newborn chicks after yolk sac inoculation. This study suggests that Salmonella Thompson can circulate between humans and poultry farms and transmit drug resistance genes and demonstrated that Salmonella Thompson is highly pathogenic to chicks and should be guarded against in the hatching stage of poultry farms.

Abstract

Salmonella Thompson, an important foodborne pathogen, is rarely found to be pathogenic to poultry. Accidentally, S. Thompson was found to be pathogenic to embryos of white feather broiler at a poultry farm in China. Therefore, this study aimed to explore antimicrobial resistance and pathogenicity of clinical S. Thompson isolated from dead poultry embryos. The phylogenetic tree based on 16S rRNA and seven housekeeping genes showed that the 14 clinical S. Thompson were closely related. The core-genome multilocus sequence typing of 14 clinical S. Thompson based on whole-genome sequencing was cgST-12774, consistent with the only two strains of S. Thompson from humans in China as reported in the NCBI database. The antimicrobial resistance gene analysis demonstrated that all strains carried aac(6′)-Iaa and the polymyxin resistance gene mcr-9. Antimicrobial sensitivity tests for 18 antibiotics showed that S. Thompson isolates displayed resistance against streptomycin (100%), ampicillin (35.7%), and doxycycline (14.3%), but sensitivity to polymyxin B, proving that the mcr-9 gene had not appeared resistance phenotype. Virulence genes Salmonella pathogenicity island (SPI) SPI1-5, type I fimbriae gene (fimA), flagellar assembly genes (bcfC, flhD, fliA, fliC, fljB, flgK, and lpfC), and other virulence genes (iroN, pagC, and cigR) were found in each S. Thompson isolate. Additionally, the bacterial inoculation experiment with 1-day-old chicks revealed that clinical S. Thompson was highly pathogenic to newborn chicks after yolk sac inoculation. This study highlighted that the S. Thompson isolated from poultry embryos and the S. Thompson causing human foodborne diarrhea in some parts of China belong to the same cgMLST typology (cgST-12774) and showed the pathogenicity of this clinical S. Thompson to chicks.

Occurrence and Characteristics of Mcrs among Gram-Negative Bacteria Causing Bloodstream Infections of Infant Inpatients between 2006 and 2019 in China

The aim of this study was to determine the occurrence of mobilized colistin resistance (mcr) genes in Gram-negative bacteria causing bloodstream infections of child inpatients in China. Bacteria were collected between 2006 and 2019 in a maternal and child health hospital, and mcr genes were screened by PCR. Five of 252 isolates were mcr-positive, including one mcr-1-positive colistin-resistant Escherichia coli isolate, two mcr-9-positive colistin-susceptible Salmonella enterica isolates, and two mcr-9-positive colistin-susceptible Enterobacter hormaechei isolates. These were obtained from two neonate and three infant patients admitted between 2009 and 2018. The E. coli isolate was obtained from a neonate aged 20 min, suggestive of a possible mother-to-neonate transmission. The five mcr-positive isolates were multidrug resistant, and two S. enterica and one E. hormaechei isolate showed a hypervirulent phenotype compared to a hypervirulent Klebsiella pneumoniae type strain in a Galleria mellonella infection model. The mcr-1 gene was carried by an IncX4-type pA1-like epidemic plasmid, and the mcr-9 gene was detected on IncHI2/2A-type novel plasmids co-carrying multiple resistance genes. The four IncHI2/2A-type plasmids shared a backbone and a high similarity (≥77% coverage and ≥ 90% nucleotide identity), suggesting that they were derived from a common ancestor with cross-species transmission and have circulated locally over a long period. The conjugation assay showed that the mcr-1-encoding plasmid and one mcr-9-encoding plasmid were self-transmissible to E. coli with high conjugation frequencies. Our findings demonstrate that mcr genes have disseminated in the community and/or hospitals, mediated by epidemic/endemic plasmids over a long period. The study shows that continuous monitoring of mcr genes is imperative for understanding and tackling their dissemination.

IMPORTANCE Antimicrobial resistance, especially the spread of carbapenemase-producing Enterobacteriaceae (CPE), represents one of the largest challenges to One Health coverage of environmental, animal, and human sectors. Colistin is one of the last-line antibiotics for clinical treatment of CPE. However, the emergence of the mobilized colistin resistance (mcr) gene largely threatens the usage of colistin in the clinical setting. In this study, we investigated the existence of mcr genes in 252 Gram-negative bacteria collected between 2006 and 2019 which caused bloodstream infections of child inpatients in China. We found a high prevalence of mcr carriage among children inpatients in the absence of professional exposure, and mcr might have widely disseminated in the community via different routes. This study emphasizes the importance of rational use of colistin in the One Health frame, and highlights both the urgent need for understanding the prevalence and dissemination of mcr genes in different populations and the importance of effective measures to control their spread.

Co-occurrence of bla NDM-1 and mcr-9 in a Conjugative IncHI2/HI2A Plasmid From a Bloodstream Infection-Causing Carbapenem-Resistant Klebsiella pneumoniae

Spread of the carbapenemase-encoding and mobilized colistin resistance (mcr) genes among Enterobacteriales poses a great threat to global public health, especially when the both genes are transferred by a single plasmid. Here, we identified a bla _NDM-1- and mcr-9-co-encoding plasmid harbored by a clinical isolate of Klebsiella pneumoniae (KPN710429). KPN710429 was recovered from a blood sample from an inpatient in a tertiary hospital in China, and antimicrobial susceptibility testing showed that it was multidrug-resistant and only susceptible to aztreonam, colistin, and tigecycline. KPN710429 belongs to sequence type (ST) 1308 and capsular serotype KL144. The string test of KPN710429 was negative, and this strain didn't exhibit a hypervirulent phenotype according to serum-killing and Galleria mellonella lethality assessments. Whole-genome sequencing revealed the KPN710429 genome comprises a single chromosome and three plasmids. All virulence associated genes were harbored by chromosome. Most of its antimicrobial resistance genes, including bla _NDM-1 and mcr-9 were carried by plasmid pK701429_2, belonging to the incompatibility (Inc) HI2/HI2A group and ST1. Comparative genomics assays indicates that pK710429_2 could be a hybrid plasmid, formed by a Tn6696-like bla _NDM-1 region inserting into a mcr-9-positive-IncHI2/HI2A plasmid. pK710429_2 contained the conjugative transfer gene regions, Tra1 and Tra2, with some structural variations, and conjugation assays revealed that pK710429_2 was transferable. Although pK710429_2 lacked the qseB-qseC regulatory genes, mcr-9 expression was upregulated after pretreatment with colistin for 6 h, leading to colistin resistance in KPN710429. To our knowledge, this is the first report of a bla _NDM-1- and mcr-9-co-encoding transferable plasmid harbored by a bloodstream-infection-causing K. pneumoniae strain in China. Effective surveillance should be implemented to assess the prevalence of the plasmid co-harboring carbapenemase-encoding gene and mcr-9.

Mobile Colistin Resistance Genetic Determinants of Non-Typhoid Salmonella enterica Isolates from Russia

Polymyxin resistance, determined by mcr genes located on plasmid DNA, currently poses a high epidemiological threat. Non-typhoid Salmonella (NTS) are one of the key pathogens causing diarrheal diseases. Here, we report the isolation and whole genome sequencing of multidrug colistin-resistant/susceptible isolates of non-typhoid Salmonella enterica serovars carrying mcr genes. Non-typhoid strains of Salmonella enterica subsp. enterica were isolated during microbiological monitoring of the environment, food, and diarrheal disease patients between 2018 and 2020 in Russia (n = 586). mcr-1 genes were detected using a previously developed qPCR assay, and whole genome sequencing of mcr positive isolates was performed by both short-read (Illumina) and long-read (Oxford Nanopore) approaches. Three colistin-resistant isolates, including two isolates of S. Enteritidis and one isolate of S. Bovismorbificans, carried the mcr-1.1 gene located on IncX4 and IncI2 conjugative plasmids, respectively. The phenotypically colistin-susceptible isolate of S. Typhimurium carried a mcr-9 gene on plasmid IncHI2. In conclusion, we present the first three cases of mcr gene-carrying NTS isolates detected in Russia with both outbreak and sporadic epidemiological backgrounds.

The surveillance of colistin resistance and mobilized colistin resistance genes in multidrug-resistant Enterobacteriaceae isolated in Japan

BACKGROUND

The plasmid-mediated bacterial colistin-resistant gene, mcr, is of global concern in clinical healthcare. However, there are few reports of surveillance for mcr in Japan. The aim of this study was to assess the prevalence of colistin resistance by identifying nine mcr genes in extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae and carbapenem-resistant Enterobacteriaceae (CRE) isolates in Japan.

METHODS

A total of 273 ESBL and CRE clinical isolates were collected from patients in five tertiary hospitals from August 2016 to March 2017. Minimum inhibitory concentration (MIC) of colistin was measured using the microdilution method. Polymerase chain reaction (PCR) was performed to detect mcr-1 to mcr-9 genes in all strains. Whole-genome sequencing (WGS) analysis was conducted for any mcr-genes identified that had not been previously reported in patients from Japan.

RESULTS

The rate of colistin resistance was 7.7% in all strains, with a higher rate in the CRE strains than in the ESBL-producing strains (20.4% versus 1.1%). The mcr-5 and mcr-9 gene were detected in one ESBL-producing Escherichia coli strain (1/273, 0.37%) and three CRE strains (3/273, 1.1%), respectively. As the ESBL-producing E. coli strain was the first clinical strain with mcr-5 in Japan, WGS analysis was performed for the strain. The sequence type of the mcr-5-positive strain was ST1642 and it carried two distinct plasmids, ESBL gene-carrying pN-ES-6-1, and mcr-5.1-carrying pN-ES-6-2.

CONCLUSIONS

The results of this study showed that the frequency of colistin resistance and mcr-positive strains is not high in Japan. As the MIC for colistin was low in the mcr-5.1 and mcr-9 gene-positive strain, continuous monitoring of mcr genes is necessary.

Corrigendum: First Report of Coexistence of bla SFO-1 and bla NDM-1 β-Lactamase Genes as Well as Colistin Resistance Gene mcr-9 in a Transferrable Plasmid of a Clinical Isolate of Enterobacter hormaechei

[This corrects the article DOI: 10.3389/fmicb.2021.676113.].

Genomic Characterization of ESBL- and Carbapenemase-Positive Enterobacteriaceae Co-harboring mcr-9 in Japan

Worldwide spread of Enterobacteriaceae resistant to colistin, a polypeptide antibacterial drug for last-resort treatment of carbapenemase-producing Enterobacteriaceae (CPE) infections, is concerning. This study aimed to elucidate colistin MICs and molecular characteristics of mcr-1 to mcr-9 of ESBL-producing Escherichia coli (ESBL-Ec) and CPE in Japan and clarify the genomic structure of strains harboring mcr genes (especially mcr-9). This study included 168 ESBL-Ec and 126 CPE strains isolated at Japanese medical facilities. Colistin susceptibility testing and multiplex PCR targeting mcr-1 to mcr-9 were performed for all strains with S1-nuclease pulsed-field gel electrophoresis, Southern blot hybridization, and whole-genome sequencing (WGS) with hybrid assembly performed for mcr gene-carrying strains. Two CPE strains showed a MIC ≥ 4 μg/ml in colistin susceptibility testing, with no known resistance mechanism detected. However, PCR conducted on all target strains detected three mcr-9-carrying strains showing colistin susceptibility. The bla_CTX–M–62-positive E. coli THUN648 strain simultaneously carried bla_CTX–M–62 and mcr-9 on a 275-kbp plasmid. Besides, bla_IMP–6 + bla_CTX–M–2-positive Klebsiella pneumoniae THUN262 and bla_GES–24-positive Enterobacter kobei THUN627 had mcr-9 encoded on the chromosome. Only THUN627 encoded qseB/C, which is suggested to be a regulatory gene for mcr-9, downstream of mcr-9. However, this strain showed no increased expression of these genes in mRNA quantitative analysis under colistin exposure. Colistin MICs of ESBL-Ec and CPE in Japan were all below 2 μg/ml, which is below the epidemiological cutoff (ECOFF) value (https://eucast.org/) or clinical breakpoint (CB) (CLSI M100-S30) reported for colistin, indicating neither “microbiological” nor “clinical” resistance. Several colistin-susceptible Enterobacteriaceae carrying silent mcr-9 encoded on plasmids and chromosomes have already spread worldwide along with other antimicrobial resistance genes. However, the mechanism of colistin resistance by mcr-9 remains unclear.

Exploring the Global Spread of Klebsiella grimontii Isolates Possessing blaVIM-1 and mcr-9

The spread of plasmid-mediated carbapenemases within Klebsiella oxytoca is well-documented. In contrast, data concerning the closely related species Klebsiella grimontii are scarce. In fact, despite the recent report of the first bla_KPC-2-producing K. grimontii, nothing is known about its clonality and antibiotic resistance patterns. In a retrospective search in our collection, we identified 2 bla_VIM-positive K. oxytoca strains. Whole-genome sequencing with both Illumina and Nanopore indicated that our strains actually belonged to K. grimontii and were of sequence type 172 (ST172) and ST189. Moreover, the two strains were associated with 297-kb IncHI2/HI2A-pST1 and 90.6-kb IncFII(Yp) plasmids carrying bla_VIM-1 together with mcr-9 and bla_VIM-1, respectively. In the IncHI2/HI2A plasmid, bla_VIM-1 was located in a class 1 integron (In110), while mcr-9 was associated with the qseC-qseB-like regulatory elements. Overall, this plasmid was shown to be very similar to those carried by other Enterobacterales isolated from food and animal sources (e.g., Salmonella and Enterobacter spp. detected in Germany and Egypt). The IncFII(Yp) plasmid was unique, and its bla_VIM-1 region was associated with a rare integron (In1373). Mapping of In1373 indicated a possible origin in Austria from an Enterobacter hormaechei carrying a highly similar plasmid. Core-genome phylogenies indicated that the ST172 K. grimontii belonged to a clone of identical Swedish and Swiss strains (≤15 single nucleotide variants [SNVs] to each other), whereas the ST189 strain was sporadic. Surveillance of carbapenemase-producing K. oxytoca strains should be reinforced to detect and prevent the dissemination of new species belonging to the Klebsiella genus.

Distribution of mcr genes among carbapenem-resistant Enterobacterales clinical isolates: High prevalence of mcr-positive Enterobacter cloacae complex in Seoul, Republic of Korea

Colistin is usually used as a drug of last resort against infections caused by multidrug-resistant gram-negative bacteria, including carbapenem-resistant Enterobacterales (CRE). Recently, the acquisition of mobile colistin resistance (mcr) genes by CRE is a cause for worry. Here, we investigated the prevalence of mcr genes in CRE isolates in Seoul, Korea. A total of 3,675 CRE strains were collected from patients between 2018 and 2019 and initially screened for mcr genes using multiplex-PCR assays. Upon the identification of mcr-harboring strains, colistin susceptibility tests, identification of carbapenemase and β-lactamase genes, and plasmid replicon typing were performed. Clonal analysis was conducted using pulsed-field gel electrophoresis. mcr genes were detected in 2.2% (80/3,675) CRE strains. There were three mcr-1, one mcr-4.3, one mcr-4.3/mcr-9, 58 mcr-9, one mcr-9/mcr-10, and 16 mcr-10 carriers from various Enterobacterales species, of which 60 were in Enterobacter cloacae complex (ECC) strains. The mcr prevalence in ECC was 20.5%. Molecular detection confirmed that 21.3% and 13.8% of the mcr-harboring strains shared bla_NDM-1 or bla_KPC-2, respectively. In addition, an IncHI2 replicon was identified in 71.7% of the mcr-9 strains. Comparative analysis revealed not only a notable diversity of mcr carriers, but also clonal spreading or nosocomial outbreak of some ECC strains. Our findings revealed a silent distribution of mcr in CRE strains with high genetic heterogeneity in Seoul, underscoring the urgent need for timely intervention to control and prevent mcr dissemination.

Detection and genomic characterization of mcr-9 in Enterobacter hormaechei recovered from a pediatric patient in Lebanon

BACKGROUND

The emergence and spread of mobilized colistin resistance (mcr) genes are a global health concern.

OBJECTIVES

In this study, we report the detection and genomic characterization of mcr-9 in a colistin-susceptible Enterobacter hormaechei (EH23) recovered from a pediatric patient in Lebanon.

RESULTS

EH23 was susceptible to colistin with a minimal inhibitory concentration (MIC) of 0.25 mg/L. Studying the mcr-9 genetic environment revealed that it was chromosomal and was bracketed by IS903 and IS26. QseCB, a two-component regulatory system, mediating the inducible expression of mcr-9 gene was not detected within the mcr-9 cassette but elsewhere on the genome. EH23 was 99.96% similar based on average nucleotide identity (ANI) to another mcr-negative E. hormaechei OIPH-N069 isolate recovered from Japan. wgSNP-based phylogenetic analysis divided all mcr-9 positive E. hormaechei isolates into five clades (I to V), with isolates from the same ST being clustered together.

CONCLUSION

The silent spread of mcr-9, particularly in the globally successful ST-78 Enterobacter lineage, is worrisome and requires close monitoring in humans and animals.

Emergence of IncHI2 Plasmids With Mobilized Colistin Resistance (mcr)-9 Gene in ESBL-Producing, Multidrug-Resistant Salmonella Typhimurium and Its Monophasic Variant ST34 From Food-Producing Animals in Italy

A collection of 177 genomes of Salmonella Typhimurium and its monophasic variant isolated in 2014-2019 from Italian poultry/livestock (n = 165) and foodstuff (n = 12), previously screened for antimicrobial susceptibility and assigned to ST34 and single-locus variants, were studied in-depth to check the presence of the novel mcr-9 gene and to investigate their genetic relatedness by whole genome sequencing (WGS). The study of accessory resistance genes revealed the presence of mcr-9.1 in 11 ST34 isolates, displaying elevated colistin minimum inhibitory concentration values up to 2 mg/L and also a multidrug-resistant (MDR) profile toward up to seven antimicrobial classes. Five of them were also extended-spectrum beta-lactamases producers (bla SHV - 12 type), mediated by the corresponding antimicrobial resistance (AMR) accessory genes. All mcr-9-positive isolates harbored IncHI2-ST1 plasmids. From the results of the Mash analysis performed on all 177 genomes, the 11 mcr-9-positive isolates fell together in the same subcluster and were all closely related. This subcluster included also two mcr-9-negative isolates, and other eight mcr-9-negative ST34 isolates were present within the same parental branch. All the 21 isolates within this branch presented an IncHI2/2A plasmid and a similar MDR gene pattern. In three representative mcr-9-positive isolates, mcr-9 was demonstrated to be located on different IncHI2/IncHI2A large-size (∼277-297 kb) plasmids, using a combined Illumina-Oxford Nanopore WGS approach. These plasmids were also compared by BLAST analysis with publicly available IncHI2 plasmid sequences harboring mcr-9. In our plasmids, mcr-9 was located in a ∼30-kb region lacking different genetic elements of the typical core structure of mcr-9 cassettes. In this region were also identified different genes involved in heavy metal metabolism. Our results underline how genomics and WGS-based surveillance are increasingly indispensable to achieve better insights into the genetic environment and features of plasmid-mediated AMR, as in the case of such IncHI2 plasmids harboring other MDR genes beside mcr-9, that can be transferred horizontally also to other major Salmonella serovars spreading along the food chain.

First Report of Coexistence of bla SFO-1 and bla NDM-1 β-Lactamase Genes as Well as Colistin Resistance Gene mcr-9 in a Transferrable Plasmid of a Clinical Isolate of Enterobacter hormaechei

Many antimicrobial resistance genes usually located on transferable plasmids are responsible for multiple antimicrobial resistance among multidrug-resistant (MDR) Gram-negative bacteria. The aim of this study is to characterize a carbapenemase-producing Enterobacter hormaechei 1575 isolate from the blood sample in a tertiary hospital in Wuhan, Hubei Province, China. Antimicrobial susceptibility test showed that 1575 was an MDR isolate. The whole genome sequencing (WGS) and comparative genomics were used to deeply analyze the molecular information of the 1575 and to explore the location and structure of antibiotic resistance genes. The three key resistance genes (bla_SFO–1, bla_NDM–1, and mcr-9) were verified by PCR, and the amplicons were subsequently sequenced. Moreover, the conjugation assay was also performed to determine the transferability of those resistance genes. Plasmid files were determined by the S1 nuclease pulsed-field gel electrophoresis (S1-PFGE). WGS revealed that p1575-1 plasmid was a conjugative plasmid that possessed the rare coexistence of bla_SFO–1, bla_NDM–1, and mcr-9 genes and complete conjugative systems. And p1575-1 belonged to the plasmid incompatibility group IncHI2 and multilocus sequence typing ST102. Meanwhile, the pMLST type of p1575-1 was IncHI2-ST1. Conjugation assay proved that the MDR p1575-1 plasmid could be transferred to other recipients. S1-PFGE confirmed the location of plasmid with molecular weight of 342,447 bp. All these three resistant genes were flanked by various mobile elements, indicating that the bla_SFO–1, bla_NDM–1, and mcr-9 could be transferred not only by the p1575-1 plasmid but also by these mobile elements. Taken together, we report for the first time the coexistence of bla_SFO–1, bla_NDM–1, and mcr-9 on a transferable plasmid in a MDR clinical isolate E. hormaechei, which indicates the possibility of horizontal transfer of antibiotic resistance genes.

Appearance of mcr-9, blaKPC, cfr and other clinically relevant antimicrobial resistance genes in recreation waters and sands from urban beaches, Brazil

The co-occurrence of mcr-like and carbapenemase-encoding genes have been reported mainly in humans and animals, whereas, in the environment, studies are gradually increasing due to the One Health approach. In this study, we investigated antimicrobial resistance genes (ARGs) in water and sand samples from marine environments in Brazil. Total DNA from 56 samples (33 sands and 23 waters) was obtained and 27 different ARGs were detected, highlighting the presence of mcr-9, bla_KPC and cfr genes. Additionally, the microbiological analysis revealed that sand samples of all analyzed beaches were not recommended for primary use, whereas water samples from most beaches were classified as unsuitable for bathing. The presence of clinically relevant ARGs in urban beaches suggests the presence of antimicrobial-resistant bacteria. Furthermore, to the best of our knowledge, this is the first report of mcr-9 and cfr genes in the environment from Brazil and recreational areas worldwide.

Molecular genetic characteristics of mcr-9-harbouring Salmonella enterica serotype Typhimurium isolated from raw milk

Among the 10 reported mcr genes, mcr-9 was first identified in Salmonella enterica serotype Typhimurium, which is a leading cause of foodborne illness worldwide. However, information about the prevalence and genetic features of mcr-9 is still lacking, especially among food samples. This study reports the presence of mcr-9 in raw milk samples from China; the prevalence rate was low (0.83%, 1/120). mcr-9 was located on a transferable plasmid, and was stable in wild-type S. enterica. However, it had a biological fitness cost when transferred to an Escherichia coli recipient. Whole-genome sequencing revealed that mcr-9 was located on the IncHI2A-type plasmid, and was surrounded by IS903B and IS26 in its flanking regions. The mcr-9-carrying S. enterica 19SE belonged to ST26 and had a multi-drug-resistant phenotype. It was confirmed that mcr-9 did not mediate colistin resistance in this study, indicating that its transfer may not facilitate the dissemination of colistin resistance.

Genomic characterization of clinical Enterobacter roggenkampii co-harbouring blaIMP-1- and blaGES-5-encoding IncP6 and mcr-9-encoding IncHI2 plasmids isolated in Japan

OBJECTIVES

The spread of carbapenemase-producing Enterobacterales (CPE) with colistin resistance is a critical public health issue. We genetically characterized the clinical isolate Enterobacter roggenkampii OIPH-N260, which harboured carbapenemase genes bla_IMP-1 and bla_GES-5 with multiple resistance genes, including mcr-9 and bla_CTX-M-9.

METHODS

This isolate was characterized by whole-genome sequencing, comparative analysis of resistance plasmids, susceptibility tests, bacterial conjugation, S1-nuclease digested pulsed-field-gel electrophoresis, and Southern blot hybridization.

RESULTS

The OIPH-N260 isolate exhibited resistance to most β-lactams and colistin. It co-harboured two resistance plasmids, the bla_IMP-1- and bla_GES-5-encoding IncP6 plasmid pN260-3 and mcr-9- and bla_CTX-M-9-encoding IncHI2 plasmid pN260-1. The comparative analysis of pN260-3 indicated that a unique bla_IMP-1-surrounding region was inserted into the bla_GES-5-encoding plasmid with the mobile element IS26, which plays an important role in the spread of resistance genes. pN260-1 did not possess the mcr-9 expression regulative gene qseBC. Both plasmids were transferable into other bacterial species via conjugation.

CONCLUSIONS

This is the first study to report not only a bla_IMP-1 and bla_GES-5 co-encoding plasmid, but also the co-harbouring of another plasmid carrying mcr-9 and bla_CTX-M-9 in Enterobacter cloacae complex. The development of advanced resistance via IS26-mediated insertion and the co-harbouring of resistance plasmids highlights the need to monitor for resistance genes in CPE.

Co-infections of two carbapenemase-producing Enterobacter hormaechei clinical strains isolated from the same diabetes individual in China

Introduction. Since mcr-1 was first reported in China, there have been ten variants of MCR appearing nationwide so far. Multidrug-resistant Enterobacteriaceae bacteria carrying both NDM and MCR have become a serious threat to global public health.Hypothesis/Gap Statement. The genetic structure of mcr-9 needs to be better understood in order to better prevent and control the transmission of drug-resistant genes.Aims. The aim of this study was to characterize the presence of two Enterobacter hormaechei isolates, which carries bla _NDM-5 CME2 and the coexistence of mcr-9 and bla _NDM-1 strain CMD2, which were isolated from a patient with diabetes in Sichuan, China.Methodology. The microbroth dilution method was used for antibiotic susceptibility. Conjugation experiment was used to investigate the transferability of bla _NDM-1, bla _NDM-5 and mcr-9. Whole-genome sequencing was performed on Illumina HiSeq platform. The ability of biofilm formation was detected by crystal-violet staining, the virulence of the bacteria was measured by Galleria mellonella killing assay.Results. bla _NDM-5 carrier CME2 and CMD2 with bla _NDM-1 and mcr-9 were resistant to carbapenems, β-lactam, aminoglycoside, quinolone and tetracycline, while CMD2 was also resistant to colistin. Conjugation assay and plasmid replicon typing further demonstrated that both bla _NDM-1 and bla _NDM-5 were respectively present on the self-transferrable IncX3 plasmid, mcr-9 was located on the self-transferrable IncHI2 plasmid. Through the analysis of mcr-9 gene context, the structure was DUF4942-rcnR-rcnA-copS-IS903-mcr-9-wbuC-qseC-qseB-IS1R-ΔsilR-IS903, bla _NDM-1 context was IS3000-ΔISAba125-IS5-bla _NDM-1-ble-trpF-groS-groL-insE-ΔIS26 structure, bla _NDM-5 structure was IS3000-bla _NDM-5-ble-trpF-dsbC-ΔIS26-umuD-ISKox3-tnpR-parA. Biofilm formation of CME2 was stronger than CMD2. There was no significant difference in virulence between the two strains.Conclusion. This study reveals two multiple drug-resistant E. hormaechei isolates from diabetes patient samples. E. hormaechei carrying two NDM-resistant genes is already a serious threat, where MCR is an important cause of treatment failure in bacterial infections. This study is a reminder not only to prevent infection in patients with diabetes, but also to constantly monitor the epidemic and spread of the drug-resistant gene.

Genomic Characterization of VIM and MCR Co-Producers: The First Two Clinical Cases, in Italy

Background: the co-production of carbapenemases and mcr-genes represents a worrisome event in the treatment of Enterobacteriaceae infections. The aim of the study was to characterize the genomic features of two clinical Enterobacter cloacae complex (ECC) isolates, co-producing VIM and MCR enzymes, in Italy. Methods: species identification and antibiotic susceptibility profiling were performed using MALDI-TOF and broth microdilution methods, respectively. Transferability of the bla_VIM- and mcr- type genes was verified through conjugation experiment. Extracted DNA was sequenced using long reads sequencing technology on the Sequel I platform (PacBio). Results: the first isolate showed clinical resistance against ertapenem yet was colistin susceptible (EUCAST 2020 breakpoints). The mcr-9.2 gene was harbored on a conjugative IncHI2 plasmid, while the bla_VIM-1 determinant was harbored on a conjugative IncN plasmid. The second isolate, resistant to both carbapenems and colistin, harbored: mcr-9 gene and its two component regulatory genes for increased expression on the chromosome, mcr-4.3 on non-conjugative (yet co-transferable) ColE plasmid, and bla_VIM-1 on a non-conjugative IncA plasmid. Conclusions: to our knowledge, this is the first report of co-production of VIM and MCR in ECC isolates in Italy.

Wide Spread of bla CTX-M-9/mcr-9 IncHI2/ST1 Plasmids and CTX-M-9-Producing Escherichia coli and Enterobacter cloacae in Rescued Wild Animals

Wildlife has recently been pinpointed as one of the drivers of dissemination of genes conferring resistances to clinically important antimicrobials. The presence of both extended-spectrum beta-lactamase- (ESBL) and carbapenemase-encoding genes has notably been reported in wild birds, that can act as sentinels of antimicrobial resistance (AMR) contamination but also as long-distance spreaders in case of migratory birds. Here, 424 wild birds brought to a rescue center in France were sampled over a 6-month period. These birds encompassed 62 different sedentary or migratory species. A further 16 wild mammals present in the center were also investigated. No carbapenemase-producer was found, but we identified a surprisingly high proportion (24.1%) of ESBL-positive isolates. A total of 144 non-duplicate isolates were collected, including Escherichia coli (n = 88), Enterobacter cloacae (n = 51), and Citrobacter freundii (n = 5), of which 123 carried the bla_CTX–M–9 gene. PFGE, phylogroup, and MLST revealed the presence of a limited number of ESBL-positive clones circulating in these animals, all presenting multiple associated resistances. Next-generation sequencing on a subset of isolates, followed by Southern blot hybridization, showed the wide dissemination of an IncHI2/ST1 plasmid carrying the bla_CTX–M–9, bla_SHV–12 and mcr-9 genes. In all, our results undoubtedly reflect cross transmissions of ESC-resistance (ESC-R) Enterobacteriaceae within the rescue center – similarly to nosocomial spreads observed at hospital, rather than the true bacterial flora of birds. We also showed that the spread of ESC-R in this rescue center did not only rely on clonal but also on a highly successful plasmidic transmission. Since most animals are intended to get back to nature after a few days or weeks, this is obviously an issue with regard to ESBL dissemination in natural environments.

First reported genome of an mcr-9-mediated colistin-resistant Salmonella Typhimurium isolate from Brazilian livestock

OBJECTIVES

To investigate the genetic context of colistin resistance in anmcr-9-harbouring Salmonella Typhimurium ST19 strain from swine in Brazil.

METHODS

Minimum inhibitory concentrations (MIC) to colistin were determined by broth microdilution. Whole-genome sequencing was performed on an Illumina MiSeq system, followed by de novo genome assembly using SPAdes 1.13.1. The draft genome sequence was annotated in Prokka using KBase online server. Downstream analyses for resistome and plasmid detection were performed using online tools available at the Center for Genomic Epidemiology. The strain was typed in silico using MLST 2.0. Phylogenetic analysis involving 24 other genomes ofSalmonella Typhimurium ST19 and mcr-9-harbouring Salmonella Typhimurium isolated from humans, livestock and foodstuff in different regions was also performed.

RESULTS

Assembly of the draft genome resulted in 5245 protein-coding sequences, 14 rRNAs, 83 tRNAs and a GC content of 51.81%. The strain was identified asSalmonella Typhimurium ST19 harbouring a 265.5-kb pN1566-2 plasmid carrying genes encoding resistance to colistin (mcr-9.1), aminoglycosides (aadA1), tetracycline [tet(C)] and sulfonamides (sul1). Our findings indicate that the Salmonella Typhimurium ST19 strain in this study showed low genetic variability compared with Salmonella Typhimurium ST19 isolated from swine and poultry in Brazil, and was less related to those reported in other countries.

CONCLUSIONS

This is the first reported genome of a phenotypically colistin-resistantSalmonella Typhimurium harbouring the mcr-9 variant in Brazilian livestock. This genome will aid global investigations on epidemiological and evolutionary aspects of plasmid-mediated colistin resistance and the role of colistin-resistant Salmonella Typhimurium ST19 lineage as a zoonotic pathogen.

First Genomic Characterization of blaVIM-1 and mcr-9-Coharbouring Enterobacter hormaechei Isolated from Food of Animal Origin

We describe here the complete genome sequence of an Enterobacter hormaechei ST279 coharbouring bla_VIM-1 and mcr-9 recovered from uncooked beef patty in June 2017, Egypt. The tested isolate was resistant to carbapenem but susceptible to colistin (minimum inhibitory concentration (MIC), 0.5 μg/mL). The antimicrobial susceptibility profile and conjugation experiments were performed. The entire genome was sequenced by the Illumina MiniSeq and Oxford Nanopore methods. The bla_VIM-1 and mcr-9 genes are carried on the same IncHI2/pMLST1 plasmid, pMS37a (Size of 270.9 kb). The mcr-9 gene was located within the physical boundaries demarcated by two insertion elements IS903 (upstream) and IS1 (downstream) but did not possess the downstream regulatory genes (qseC/qseB) which regulate the expression of mcr-9. Therefore, the mcr-9 might be silently disseminated among carbapenem-resistant Enterobacterales. In addition to bla_VIM-1 and mcr-9, plasmid pMS37a harbored various antibiotic resistance genes including aac(6’)-Il, ΔaadA22, aac(6’)-Ib-cr, sul1, dfrA1 and tetA. To the best of our knowledge, this is the first report of a bla_VIM-1 and mcr-9-coharbouring E. hormaechei isolate of food origin worldwide. The identification of a multidrug-resistant VIM-1 and mcr-9 positive Enterobacter hormaechei isolate from food is worrisome as retail meat and meat products could serve as a vehicle for these MDR bacteria, which could be transferred between animals and humans through the food chain. It further highlights that Enterobacterales co-producing MCR and carbapenemases being found in the food chain indeed correspond to a One-Health issue, highlighting the need for serious steps to prevent their further dissemination.

Emergence of Transferable mcr-9 Gene-Carrying Colistin-Resistant Salmonella enterica Dessau ST14 Isolated from Retail Chicken Meat in Korea

Colistin is an important antibiotic currently used to manage infections caused by multidrug-resistant pathogens in both humans and livestock animals. A new mobile colistin-resistance (mcr-9) gene was recently discovered; this discovery highlighted the need for rigorous monitoring of bacterial resistance against colistin. Salmonella is one of the major pathogens responsible for foodborne illnesses; however, there is minimal information regarding the presence of mcr genes in foodborne Salmonella strains. The aim of this study was to investigate the presence of mcr genes among 178 Salmonella strains isolated from chicken meat in Korea. Antimicrobial susceptibility was measured using the broth microdilution method. Bioinformatics characterization of colistin-resistant strains and genetic environment of the mcr-9 gene were analyzed using next-generation sequencing. Transferability of the mcr-9 carrying colistin-resistant Salmonella strain was tested using broth-mating conjugation. Thirteen of the 178 Salmonella isolates showed colistin resistance, but only one strain, Salmonella Dessau ST14 (KUFSE-SAL043) from a traditional chicken market in Korea, carried an mcr family gene, mcr-9. This strain also carried other acquired antimicrobial resistance genes such as bla_TEM-1B, qnrS1, and aac(6')-Iaa. Only the IncX1 plasmid replicon type was detected in this strain. In the strain KUFSE-SAL043, the mcr-9 gene was located between two insertion sequences, IS903B and IS26, followed by the downstream regulatory genes qseB-like and qseC-like, which were located between IS1R and ΔIS1R. Conjugation tests revealed that the mcr-9 gene was successfully transferred to Escherichia coli J53 at a mean frequency of 2.03 × 10^-7. This is the first report of a transferable mcr-9 gene in Salmonella isolated from chicken meat in Korea, highlighting the possibility of transfer of colistin resistance. Therefore, the wide use of colistin should be reconsidered, and a One Health perspective should be adopted to monitor the antimicrobial resistance of Enterobacteriaceae strains in humans, livestock, and the environment.

Co-Occurrence of mcr-9 and bla NDM-1 in Enterobacter cloacae Isolated from a Patient with Bloodstream Infection

Background

Bloodstream infection (BSI) caused by carbapenem-resistant Enterobacteriaceae are potentially life-threatening related to poorer outcomes. Colistin is considered one of the last-resort treatments against human infections caused by multidrug-resistant (MDR) Gram-negative bacteria. Therefore, emergence of strains from the blood that co-harboring mcr and carbapenem resistance genes were considered as a serious problem.

Purpose

In this study, two mcr-9-harboring MDR Enterobacter cloacae isolates BSI034 and BSI072 recovered from BSI patients were identified, one of which co-harbored mcr-9 and bla_NDM-1. The genetic characteristics of the MDR plasmid needed to be clarified.

Methods

S1-PFGE and Southern blotting were conducted to determine the location of mcr-9. Whole-genome sequencing was performed to obtain the complete genome and plasmid sequences. The resistome and virulence genes of the strains, accompanied by the genetic characteristics of mcr-9- and bla_NDM-1-harboring plasmids, were analyzed.

Results

Whole-genome sequencing showed that BSI034 harbored mcr-9-carrying IncHI2-type pBSI034-MCR9 and bla_NDM-1-carrying IncX3-type pBSI034-NDM1. The 278,517 bp pBSI034-MCR9 carried mcr-9 along with the other 19 resistance genes. mcr-9 was flanked by IS903B (1057 bp) and IS26 (820 bp) in the same orientation. In addition to resistance genes, strain BSI034 also carried a chromosome-located Yersinia high-pathogenicity island, which harbored genes of yersiniabactin biosynthesis operon ybtSXQPAUTE, irp1/2, and fyuA.

Conclusion

We described the complete genome and mcr-9/bla_NDM-1-co-harboring plasmid of E. cloacae from a BSI patient. Notable differences were observed within mosaic modules between pBSI034-MCR9 and other mcr-9-harboring plasmids due to extensive recombination via horizontal gene transfer.

Emergence of a Multidrug-Resistant Enterobacter hormaechei Clinical Isolate from Egypt Co-Harboring mcr-9 and blaVIM-4

This study describes the first full genomic sequence of an mcr-9 and bla_VIM-4-carrying multidrug-resistant Enterobacter hormaechei clinical isolate from Egypt. The strain was isolated in April 2015 from the sputum of a patient in Cairo, Egypt. The mcr-9 and bla_VIM-4 genes were identified by PCR screening and DNA sequencing; the isolate was subjected to antimicrobial susceptibility testing, conjugation experiments, and whole genomic sequencing. mcr-9 and bla_VIM-4 were carried by an IncHI2 plasmid, pAMS-38a (281,121 bp in size); the plasmid also carried genes conferring resistance against sulfonamides (sul1), quinolones (qnrA1), trimethoprim (dfrA1), β-lactams (bla_TEM-1B), aminoglycosides (aac (6’)-II, aadA23, aadA2b, and ant(2’’)-Ia). The strain was susceptible to colistin (MIC, <0.25 μg/mL); this could be due to the absence of the qseC/qseB regulatory system located downstream of mcr-9 in Enterobacterales, which is involved in the induction of colistin-resistance. The genetic context of mcr-9 and bla_VIM-4 was identified as IS1-mcr-9-IS903-pcoS-∆pcoE-rcnA and intI1-bla_VIM-4—aac (6’)-II-dfrA1-∆aadA23-smr-ISPa21-qacE∆1, respectively. This is the first report of an mcr-9 and bla_VIM-4 /IncHI2-carrying multidrug-resistant E. hormaechei clinical isolate from Africa and the Middle East. Plasmids of the IncHI2 group and the two insertion sequences (IS1, and IS903) might be the main vehicles for dissemination of mcr-9. Further screening for mcr-9 is essential for identifying its incidence and to prevent its dissemination.

Coproduction Of MCR-9 And NDM-1 By Colistin-Resistant Enterobacter hormaechei Isolated From Bloodstream Infection

Background

Colistin acts as the last line of defense against severe infections caused by carbapenem-resistant Enterobacteriaceae. Infections caused by extensively drug-resistant isolates coproducing MCR and carbapenemases have posed a serious public health concern.

Purpose

In this study, we reported the first clinical colistin and carbapenem-resistant Enterobacter hormaechei isolate SCNJ07 coharboring bla _NDM-1 and mcr-9 from a patient with bloodstream infection in China.

Methods

Bacterial antimicrobial susceptibility testing was performed using the broth microdilution method. Conjugation assay was carried out to investigate the transferability of mcr-9 and bla _NDM-1. Whole-genome sequencing of strain SCNJ07 was performed using an Illumina HiSeq system and the genetic characteristics of the mcr-9- and bla _NDM-1-harboring plasmids were analyzed.

Results

Conjugation assays revealed that both bla _NDM-1 and mcr-9 genes could successfully transfer their resistance phenotype to Escherichia coli strain J53. Whole genome sequencing showed that SCNJ07 possessed an FIB36:FIIY4 type self-transmissible plasmid bearing bla _NDM-1, which possessed high similarity to previously reported pRJF866 in China. mcr-9 was located on a ~28-kb self-transmissible plasmid pMCR-SCNJ07 with both IncHI2 and IncR replicons. Two copies of intact IS903 that bracketed a ~8-kb region containing the mcr-9 gene were identified in pMCR-SCNJ07. BLASTn analysis revealed that a number of mcr-9-positive plasmids have been around for a while among Enterobacteriaceae worldwide.

Conclusion

This study reveals the likelihood of a wide dissemination of this newly identified colistin resistance gene mcr-9 among Enterobacteriaceae. Further surveillance is urgently needed to understand the prevalence and dissemination of mcr-9, thereby facilitating establishment of measures to control its spread.

First Report of bla VIM-4- and mcr-9-Coharboring Enterobacter Species Isolated from a Pediatric Patient

We describe the complete genome assembly and sequence of a clinical Enterobacter isolate harboring both bla_VIM-4 and mcr-9 recovered from a pediatric patient in the United States with a history of travel to Egypt. Moreover, to the best of our knowledge, this is the first report of an Enterobacter isolate harboring both bla_VIM-4 and mcr-9 from the United States. The bla_VIM-4 and mcr-9 genes are carried on the same IncH12 plasmid, pME-1a. The isolate tested susceptible to colistin, without observed induction of colistin resistance. The mcr-9 gene is located between two insertion elements, IS903 and IS1, but lacks the downstream regulatory genes (qseC and qseB) found in other isolates that harbor mcr-9.

An Enterobacter hormaechei isolate harboring bla_VIM-4 and mcr-9 was recovered from a pediatric patient in a U.S. hospital. The bla_VIM-4 and mcr-9 genes are carried on the same IncH12 plasmid, pME-1a. The isolate tested susceptible to colistin, without observed induction of colistin resistance. The mcr-9 gene is located between two insertion elements, IS903 and IS1, but lacks the downstream regulatory genes (qseC and qseB) found in other isolates that harbor mcr-9.

IMPORTANCE We describe the complete genome assembly and sequence of a clinical Enterobacter isolate harboring both bla_VIM-4 and mcr-9 recovered from a pediatric patient in the United States with a history of travel to Egypt. Moreover, to the best of our knowledge, this is the first report of an Enterobacter isolate harboring both bla_VIM-4 and mcr-9 from the United States. The bla_VIM-4 and mcr-9 genes are carried on the same IncH12 plasmid, pME-1a. The isolate tested susceptible to colistin, without observed induction of colistin resistance. The mcr-9 gene is located between two insertion elements, IS903 and IS1, but lacks the downstream regulatory genes (qseC and qseB) found in other isolates that harbor mcr-9.

A link between the newly described colistin resistance gene mcr-9 and clinical Enterobacteriaceae isolates carrying blaSHV-12 from horses in Sweden

OBJECTIVES

The aim of this study was to investigate the occurrence of the newly described transferable colistin resistance gene mcr-9 in extended-spectrum β-lactamase (ESBL)-producing clinical Enterobacteriaceae isolates from horses in Sweden.

METHODS

A total of 56 whole-genome sequenced ESBL-producing Enterobacteriaceae isolates from horses were subjected to in silico detection of antimicrobial resistance genes and identification of plasmid replicons types. The colistin minimum inhibitory concentration (MIC) for mcr-positive isolates was determined by broth microdilution. Relatedness between Enterobacteriaceae carrying mcr genes was determined by multilocus sequence typing (MLST) and core genome MLST.

RESULTS

Thirty ESBL-producing Enterobacteriaceae isolates from horses were positive for the colistin resistance gene mcr-9. These isolates included Enterobacter cloacae, Escherichia coli, Klebsiella oxytoca and Citrobacter freundii and belonged to diverse MLST sequence types within each species. Two of the mcr-9-containing isolates originated from the same horse. All mcr-9-positive isolates had colistin MICs below or equal to the EUCAST epidemiological cut-off value of 2 mg/L and were negative for the two potential regulatory genes qseB-like and qseC-like for mcr-9. Except for one isolate carrying only bla_TEM-1B, all of the isolates carried bla_SHV-12 and bla_TEM-1B, and were all considered multidrug-resistant as they harboured genes encoding resistance to aminoglycosides, chloramphenicol, fosfomycin, macrolides, quinolones, sulfonamides, trimethoprim and tetracyclines. Plasmid replicon types IncHI2 and IncHI2A were detected in all mcr-9-positive isolates.

CONCLUSION

The occurrence of mcr-9 was common among clinical ESBL-producing Enterobacteriaceae isolates from horses in Sweden and was linked to the ESBL-encoding gene bla_SHV-12 and plasmid replicon types IncHI2 and IncHI2A.

Identification of Novel Mobilized Colistin Resistance Gene mcr-9 in a Multidrug-Resistant, Colistin-Susceptible Salmonella enterica Serotype Typhimurium Isolate

Mobilized colistin resistance (mcr) genes are plasmid-borne genes that confer resistance to colistin, an antibiotic used to treat severe bacterial infections. To date, eight known mcr homologues have been described (mcr-1 to -8). Here, we describe mcr-9, a novel mcr homologue detected during routine in silico screening of sequenced Salmonella genomes for antimicrobial resistance genes. The amino acid sequence of mcr-9, detected in a multidrug-resistant (MDR) Salmonella enterica serotype Typhimurium (S Typhimurium) strain isolated from a human patient in Washington State in 2010, most closely resembled mcr-3, aligning with 64.5% amino acid identity and 99.5% coverage using Translated Nucleotide BLAST (tblastn). The S. Typhimurium strain was tested for phenotypic resistance to colistin and was found to be sensitive at the 2-mg/liter European Committee on Antimicrobial Susceptibility Testing breakpoint under the tested conditions. mcr-9 was cloned in colistin-susceptible Escherichia coli NEB5α under an IPTG (isopropyl-β-d-thiogalactopyranoside)-induced promoter to determine whether it was capable of conferring resistance to colistin when expressed in a heterologous host. Expression of mcr-9 conferred resistance to colistin in E. coli NEB5α at 1, 2, and 2.5 mg/liter colistin, albeit at a lower level than mcr-3 Pairwise comparisons of the predicted protein structures associated with all nine mcr homologues (Mcr-1 to -9) revealed that Mcr-9, Mcr-3, Mcr-4, and Mcr-7 share a high degree of similarity at the structural level. Our results indicate that mcr-9 is capable of conferring phenotypic resistance to colistin in Enterobacteriaceae and should be immediately considered when monitoring plasmid-mediated colistin resistance.IMPORTANCE Colistin is a last-resort antibiotic that is used to treat severe infections caused by MDR and extensively drug-resistant (XDR) bacteria. The World Health Organization (WHO) has designated colistin as a "highest priority critically important antimicrobial for human medicine" (WHO, Critically Important Antimicrobials for Human Medicine, 5th revision, 2017, https://www.who.int/foodsafety/publications/antimicrobials-fifth/en/), as it is often one of the only therapies available for treating serious bacterial infections in critically ill patients. Plasmid-borne mcr genes that confer resistance to colistin pose a threat to public health at an international scale, as they can be transmitted via horizontal gene transfer and have the potential to spread globally. Therefore, the establishment of a complete reference of mcr genes that can be used to screen for plasmid-mediated colistin resistance is essential for developing effective control strategies.