Carbapenem and Colistin Resistance in Enterobacter: Determinants and Clones

Surveillance and Genomic Characterisation of Colistin-Resistant Gram-Negative Bacteria in the Drains of High-Risk Hospital Units

OBJECTIVE

The health care water environment, including sinks and drainage systems, can be a long-term reservoir of nosocomial pathogens. In this study, we aimed to investigate the presence of colistin-resistant Gram-negative (ColR-GN) bacteria in humid compartments of high-risk hospital units at the University Medical Center Groningen, The Netherlands.

METHODS

Environmental sampling was conducted in sink and shower drains of high-risk hospital units, and colistin MICs were determined using broth microdilution. Whole-genome sequencing was performed to investigate the presence of mobile colistin resistance (mcr) genes, chromosomal point mutations and gene alterations linked to colistin resistance.

RESULTS

ColR-GN bacteria were detected in all investigated units, with Enterobacter spp. being the most abundant genus. Twelve isolates exhibited colistin resistance (MIC >2 mg/L), including Enterobacter cloacae complex (n = 11) and Klebsiella pneumoniae (n = 1). Chromosomal mutations in genes involved in lipopolysaccharide structure modifications were the main mechanisms contributing to colistin resistance in Enterobacter spp. and Klebsiella spp. (91.6%, 11/12). Additionally, two Enterobacter kobei isolates harboured mobile colistin resistance genes, mcr-4.3 and mcr-9.1.

CONCLUSIONS

The presence and persistence of bacterial ColR-GN clones in the sink and shower drains of high-risk hospital units highlights the importance of monitoring such environments for antibiotic-resistant bacteria to identify reservoirs and prevent further spread.

ESKAPE in China: epidemiology and characteristics of antibiotic resistance

The escalation of antibiotic resistance and the diminishing antimicrobial pipeline have emerged as significant threats to public health. The ESKAPE pathogens - Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. - were initially identified as critical multidrug-resistant bacteria, demanding urgently effective therapies. Despite the introduction of various new antibiotics and antibiotic adjuvants, such as innovative β-lactamase inhibitors, these organisms continue to pose substantial therapeutic challenges. People's Republic of China, as a country facing a severe bacterial resistance situation, has undergone a series of changes and findings in recent years in terms of the prevalence, transmission characteristics and resistance mechanisms of antibiotic resistant bacteria. The increasing levels of population mobility have not only shaped the unique characteristics of antibiotic resistance prevalence and transmission within People's Republic of China but have also indirectly reflected global patterns of antibiotic-resistant dissemination. What's more, as a vast nation, People's Republic of China exhibits significant variations in the levels of antibiotic resistance and the prevalence characteristics of antibiotic resistant bacteria across different provinces and regions. In this review, we examine the current epidemiology and characteristics of this important group of bacterial pathogens, delving into relevant mechanisms of resistance to recently introduced antibiotics that impact their clinical utility in China.

Active Surveillance of Patients Colonized with CRE: A Single-Center Study Based on a Combined Molecular/Culture Protocol

Background/Objectives: Carbapenem-resistant Enterobacteriaceae (CRE) are types of bacteria that need urgent attention globally. Active surveillance programs at hospitals are essential for the early identification of CRE carriers and the timely adoption of infection control measures. We aimed to analyze the epidemiology of CRE identified by multiplex RT-PCR in rectal swabs of patients upon admission to high-risk wards and to compare data obtained from both molecular and culture CRE screening. Methods: A total of 2861 rectal swabs, prospectively collected within 12-24 h of admission, underwent molecular screening for identification of K. pneumoniae carbapenemase (KPC), New Delhi metallo-β-lactamase (NDM), Verona integron-mediated metallo-β-lactamase (VIM), imipenemase (IMP), and OXA-48 (AllplexTM Entero-DR Assay). Only samples that tested positive or invalid underwent culture testing (Agar MacConkey and CHROMID® CARBA plates, bioMérieux, Craponne, France). Results: A total of 118 out of 2861 (about 4%) were positive for at least one carbapenem-resistant gene by a molecular approach (MA), with KPC, NDM, and VIM having the highest prevalence. Culture testing confirmed the presence of carbapenemase in 89 samples (75.4%), showing a disagreement rate of about 25% between the two methods, which, unfortunately, rises up to 60% for VIM. The dominant bacterial species were K. pneumoniae and E. coli (MALDI-TOF mass spectrometry). Conclusions: Our data underlined the need for the molecular screening of CRE carriers in order to implement active surveillance protocol in critical care settings and to improve infection control measures.

Enterobacter adelaidei sp. nov. Isolation of an extensively drug resistant strain from hospital wastewater in Australia and the global distribution of the species

BACKGROUND

Enterobacter species are included among the normal human gut microflora and persist in a diverse range of other environmental niches. They have become important opportunistic nosocomial pathogens known to harbour plasmid-mediated multi-class antimicrobial resistance (AMR) determinants. Global AMR surveillance of Enterobacterales isolates shows the genus is second to Klebsiella in terms of frequency of carbapenem resistance. Enterobacter taxonomy is confusing and standard species identification methods are largely inaccurate or insufficient. There are currently 27 named species and a total of 46 taxa in the genus distinguishable via average nucleotide identity (ANI) calculation between pairs of genomic sequences. Here we describe an Enterobacter strain, ECC3473, isolated from the wastewater of an Australian hospital whose species could not be determined by standard methods nor by ribosomal RNA gene multi-locus typing.

AIM

To characterise ECC3473 in terms of phenotypic and genotypic antimicrobial resistance, biochemical characteristics and taxonomy as well as to determine the global distribution of the novel species to which it belongs.

METHODS

Standard broth dilution and disk diffusion were used to determine phenotypic AMR. The strain's complete genome, including plasmids, was obtained following long- and short read sequencing and a novel long/short read hybrid assembly and polishing, and the genomic basis of AMR was determined. Phylogenomic analysis and quantitative measures of relatedness (ANI, digital DNA-DNA hybridisation, and difference in G+C content) were used to study the taxonomic relationship between ECC3473 and Enterobacter type-strains. NCBI and PubMLST databases and the literature were searched for additional members of the novel species to determine its global distribution.

RESULTS

ECC3473 is one of 21 strains isolated globally belonging to a novel Enterobacter species for which the name, Enterobacter adelaidei sp. nov. is proposed. The novel species was found to be resilient in its capacity to persist in contaminated water and adaptable in its ability to accumulate multiple transmissible AMR determinants.

CONCLUSION

E. adelaidei sp. nov. may become increasingly important to the dissemination of AMR.

Methodological Evaluation of Carbapenemase Detection by Different Methods

The global proliferation of carbapenemase-producing bacteria (CPB) has garnered significant attention worldwide. Early diagnosis of CPB and accurate identification of carbapenemases are crucial for preventing the spread of CPB and ensuring targeted antibiotic therapy. Therefore, efficient and accurate identification of carbapenemases is paramount in clinically treating diseases associated with CPB. In this study, 58 CPB strains were collected and detected using the DNA endonuclease-targeted CRISPR trans reporter (DETECTR) method, a rapid detection platform based on CRISPR-Cas12a gene editing and isothermal amplification. Additionally, four conventional methods (the APB/EDTA method, PCR, NG-test Carba 5, and GeneXpert Carba-R) were employed and compared against whole genome sequencing (WGS) results, considered the gold standard, to evaluate their efficacy in detecting carbapenemases. Detection by the APB/EDTA method revealed that 29 strains were positive for Class A serine endopeptidases, while 29 strains were positive for Class B metalloenzymes. The classification of these zymotypes was consistent with the sequencing result. All target carbapenemases for KPC were identified with 100% sensitivity using NG-test Carba 5, PCR, DETECTR, and GeneXpert Carba-R. In the case of NDM, both Xpert Carba-R and DETECTR showed a sensitivity of 100%. In contrast, NG-test Carba 5 and PCR had a slightly lower sensitivity of 96.7%, each missing one target carbapenemase. n this study, the APB/EDTA method is capable of identifying the zymotype classification but not the specific resistant genes, while Xpert Carba-R and DETECTR are able to detect all target carbapenemases.

Emergence of bla NDM-1-carrying Enterobacter chengduensis in China

Introduction

Enterobacter chengduensis was defined as a novel species in the genus. Enterobacter in 2019, however, antimicrobial resistance, such as carbapenem resistance, has rarely been described in E. chengduensis. This study described the molecular features of four carbapenem-resistant E. chengduensis strains collected from a tertiary health care hospital in Southwest China.

Methods

Whole genome sequencing (WGS) was used to determine the genome sequence of four E. chengduensis strains. The precise species of strains were identified by average nucleotide identity (ANI) and in silico DNA-DNA hybridization (isDDH). The clonal relatedness of four E. chengduensis strains and additional 15 ones from NCBI were examined through phylogenetic analysis. The molecular features of E. chengduensis and genetic structure of carbapenemase- encoding plasmids were characterized through genomic annotation and analysis.

Results

The results revealed the emergence of bla NDM-1-carrying E. chengduensis strains in China. Multilocus sequence typing (MLST) analysis showed that all 19 E. chengduensis belonged to the same sequence type of ST414. Core SNP analysis suggested the potential intrahospital clonal transmission of ST414 E. chengduensis. The carbapenemase-encoding gene bla NDM-1 was harbored by an IncC-type plasmid, which was experimentally confirmed to be able to conjugate.

Discussion

This study reports the first emergence and potential clonal transmission of bla NDM-1-carrying E. chengduensis. Further surveillance should be advocated to monitor the dissemination of carbapenem-resistant E. chengduensis and bla NDM-1-harboring IncC-type plasmids in China.

Two novel Enterobacter species, Enterobacter chinensis sp. nov. and Enterobacter rongchengensis sp. nov., recovered from clinical samples carrying multiple virulence factors

Two Enterobacter strains 170198T and 170250T were isolated from clinical blood samples from distinct patients in a hospital in Chengdu, China, in 2022. These isolates were subjected to whole-genome sequencing. A phylogenomic tree based on 2,096 concatenated core genes showed that the two strains were clustered within the genus Enterobacter. The average nucleotide identity (ANI) and in silico DNA-DNA hybridization (isDDH) values between each of the two strains and type strains of all currently known Enterobacter species were determined. The two strains belonged to two novel species as the highest ANI and isDDH values with type strains of all currently known Enterobacter species below the cutoff for species demarcation (96% for ANI and 70% for isDDH). Then the physiological and biochemical studies demonstrated that biochemical features and the profile of whole fatty acids of strains 170198T and 170250T were largely consistent with those known Enterobacter species. Nevertheless, the two novel species can be differentiated from all other Enterobacter species by certain biochemical characteristics. In conclusion, 170198T and 170250T represent two novel species of the genus Enterobacter, for which we propose Enterobacter chinensis sp. nov. and Enterobacter rongchengensis sp. nov., as the species names. The type strains of Enterobacter chinensis sp. nov., and Enterobacter rongchengensis sp. nov. are 170198T (=GDMCC 1.3549T=JCM 35826T) and 170250T (=GDMCC 1.3670T=JCM 36189T), respectively. The two novel species have clinical significance with the ability to cause bloodstream infections.IMPORTANCEEnterobacter is a group of bacteria comprising several common opportunistic pathogens and has a complicated taxonomy. Here, we reported two novel Enterobacter species. We demonstrated that the two novel species can be differentiated from other Enterobacter species by certain phenotypic characteristics and therefore provide information for designing tests for identification. We also showed that strains of the two novel species are able to cause human bloodstream infections and carry multiple virulence factors and therefore are of clinical significance. We highlight that the virulence of Enterobacter is less studied and warrants further exploration. We believe that the findings here are valuable for enhancing the appreciation toward Enterobacter, an important pathogen.

Some virulence genes are associated with antibiotic susceptibility in Enterobacter cloacae complex

BACKGROUND

Enterobacter cloacae complex (ECC) including different species are isolated from different human clinical samples. ECC is armed by many different virulence genes (VGs) and they were also classified among ESKAPE group by WHO recently. The present study was designed to find probable association between VGs and antibiotic susceptibility in different ECC species.

METHODS

Forty-five Enterobacter isolates that were harvested from different clinical samples were classified in four different species. Seven VGs were screened by PCR technique and antibiotic susceptibility assessment was performed by disk-diffusion assay.

RESULT

Four Enterobacter species; Enterobacter cloacae (33.3%), Enterobacter hormaechei (55.6%), Enterobacter kobei (6.7%) and Enterobacter roggenkampii (4.4%) were detected. Minimum antibiotic resistance was against carbapenem agents and amikacin even in MDR isolates. 33.3% and 13.3% of isolates were MDR and XDR respectively. The rpoS (97.8%) and csgD (11.1%) showed maximum and minimum frequency respectively. Blood sample isolated were highly virulent but less resistant in comparison to the other sample isolates. The csgA, csgD and iutA genes were associated with cefepime sensitivity.

CONCLUSION

The fepA showed a predictory role for differentiating of E. hormaechei from other species. More evolved iron acquisition system in E. hormaechei was hypothesized. The fepA gene introduced as a suitable target for designing novel anti-virulence/antibiotic agents against E. hormaechei. Complementary studies on other VGs and ARGs and with bigger study population is recommended.

Genomic Study of High-Risk Clones of Enterobacter hormaechei Collected from Tertiary Hospitals in the United Arab Emirates

Enterobacter hormaechei has emerged as a significant pathogen within healthcare settings due to its ability to develop multidrug resistance (MDR) and survive in hospital environments. This study presents a genome-based analysis of carbapenem-resistant Enterobacter hormaechei isolates from two major hospitals in the United Arab Emirates. Eight isolates were subjected to whole-genome sequencing (WGS), revealing extensive resistance profiles including the blaNDM-1, blaOXA-48, and blaVIM-4 genes. Notably, one isolate belonging to ST171 harbored dual carbapenemase genes, while five isolates exhibited colistin resistance without mcr genes. The presence of the type VI secretion system (T6SS), various adhesins, and virulence genes contributes to the virulence and competitive advantage of the pathogen. Additionally, our isolates (87.5%) possessed ampC β-lactamase genes, predominantly blaACT genes. The genomic context of blaNDM-1, surrounded by other resistance genes and mobile genetic elements, highlights the role of horizontal gene transfer (HGT) in the spread of resistance. Our findings highlight the need for rigorous surveillance, strategic antibiotic stewardship, and hospital-based WGS to manage and mitigate the spread of these highly resistant and virulent pathogens. Accurate identification and monitoring of Enterobacter cloacae complex (ECC) species and their resistance mechanisms are crucial for effective infection control and treatment strategies.

Recent advances in the development of antimicrobial peptides against ESKAPE pathogens

Multi-drug resistant ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are a global health threat. The severity of the problem lies in its impact on mortality, therapeutic limitations, the threat to public health, and the costs associated with managing infections caused by these resistant strains. Effectively addressing this challenge requires innovative approaches to research, the development of new antimicrobials, and more responsible antibiotic use practices globally. Antimicrobial peptides (AMPs) are a part of the innate immune system of all higher organisms. They are short, cationic and amphipathic molecules with broad-spectrum activity. AMPs interact with the negatively charged bacterial membrane. In recent years, AMPs have attracted considerable interest as potential antibiotics. However, AMPs have low bioavailability and short half-lives, which may be circumvented by chemical modification. This review presents recent in vitro and in silico strategies for the modification of AMPs to improve their stability and application in preclinical experiments.

Drug efflux and lipid A modification by 4-L-aminoarabinose are key mechanisms of polymyxin B resistance in the sepsis pathogen Enterobacter bugandensis

OBJECTIVES

A concern with the ESKAPE pathogen, Enterobacter bugandensis, and other species of the Enterobacter cloacae complex, is the frequent appearance of multidrug resistance against last-resort antibiotics, such as polymyxins.

METHODS

Here, we investigated the responses to polymyxin B (PMB) in two PMB-resistant E. bugandensis clinical isolates by global transcriptomics and deletion mutagenesis.

RESULTS

In both isolates, the genes of the CrrAB-regulated operon, including crrC and kexD, displayed the highest levels of upregulation in response to PMB. ∆crrC and ∆kexD mutants became highly susceptible to PMB and lost the heteroresistant phenotype. Conversely, heterologous expression of CrrC and KexD proteins increased PMB resistance in a sensitive Enterobacter ludwigii clinical isolate and in the Escherichia coli K12 strain, W3110. The efflux pump, AcrABTolC, and the two component regulators, PhoPQ and CrrAB, also contributed to PMB resistance and heteroresistance. Additionally, the lipid A modification with 4-L-aminoarabinose (L-Ara4N), mediated by the arnBCADTEF operon, was critical to determine PMB resistance. Biochemical experiments, supported by mass spectrometry and structural modelling, indicated that CrrC is an inner membrane protein that interacts with the membrane domain of the KexD pump. Similar interactions were modeled for AcrB and AcrD efflux pumps.

CONCLUSION

Our results support a model where drug efflux potentiated by CrrC interaction with membrane domains of major efflux pumps combined with resistance to PMB entry by the L-Ara4N lipid A modification, under the control of PhoPQ and CrrAB, confers the bacterium high-level resistance and heteroresistance to PMB.

Genome sequence-based identification of Enterobacter strains and description of Enterobacter pasteurii sp. nov

IMPORTANCE

Accurate taxonomy is essential for microbial biological resource centers, since the microbial resources are often used to support new discoveries and subsequent research. Here, we used genome sequence data, alongside matrix-assisted laser desorption/ionization time-of-flight mass spectrometer biotyper-based protein profiling, to accurately identify six Enterobacter cloacae complex strains. This approach effectively identified distinct species within the E. cloacae complex, including Enterobacter asburiae, "Enterobacter xiangfangensis," and Enterobacter quasihormaechei. Moreover, the study revealed the existence of a novel species within the Enterobacter genus, for which we proposed the name Enterobacter pasteurii sp. nov. In summary, this study demonstrates the significance of adopting a genome sequence-driven taxonomy approach for the precise identification of bacterial strains in a biological resource center and expands our understanding of the E. cloacae complex.

Pervasive gene deregulation underlies adaptation and maladaptation in trimethoprim-resistant E. coli

IMPORTANCE

Bacteria employ a number of mechanisms to adapt to antibiotics. Mutations in transcriptional regulators alter the expression levels of genes that can change the susceptibility of bacteria to antibiotics. Two-component signaling proteins are a major class of signaling molecule used by bacteria to regulate transcription. In previous work, we found that mutations in MgrB, a feedback regulator of the PhoQP two-component system, conferred trimethoprim tolerance to Escherichia coli. Here, we elucidate how mutations in MgrB have a domino-like effect on the gene regulatory network of E. coli. As a result, pervasive perturbation of gene regulation ensues. Depending on the environmental context, this pervasive deregulation is either adaptive or maladaptive. Our study sheds light on how deregulation of gene expression can be beneficial for bacteria when challenged with antibiotics, and why regulators like MgrB may have evolved in the first place.

Epidemiological characteristics and molecular features of carbapenem-resistant Enterobacter strains in China: a multicenter genomic study

Epidemiological characteristics and molecular features of carbapenem-resistant Enterobacter (CR-Ent) species remain unclear in China. In this study, we performed a genomic study on 92 isolates from Enterobacter-caused infections from a multicenter study in China. Whole genome sequencing (WGS) was used to determine the genome sequence of 92 non-duplicated CR-Ent strains collected from multiple tertiary health centres. The precise species of Enterobacter strains were identified by average nucleotide identity (ANI) and in silico DNA-DNA hybridization (isDDH). Molecular features of high-risk CR-Ent sequence type (ST) lineages and carbapenemase-encoding plasmids were determined. The result revealed that the most common human-source CR-Ent species in China was E. xiangfangensis (66/92, 71.93%), and the proportion of carbapenemase-producing Enterobacter (CP-Ent) in CR-Ent was high (72/92, 78.26%) in comparison to other global regions. Furthermore, ST171 and ST116 E. xiangfangensis were the major lineages of CP-Ent strains, and ST171 E. xiangfangensis was more likely to cause infections in older patients. Genomic analysis also highlighted the likelihood of intra-hospital/inter-hospital clonal transmission of ST171 and ST116 E. xiangfangensis. In addition, the bla_NDM-harbouring IncX3-type plasmid was identified as the prevalent carbapenemase-encoding plasmid carried by CR-Ent strains, and was experimentally confirmed to be able to self-transfer with high frequency. This study detailed the genomic and clinical characteristics of CR-Ent in China in the form of multicenter for the first time. The high risk of carbapenemase-producing ST171 and ST116 E. xiangfangensis, and the bla_NDM-harbouring IncX3-type plasmid were detected and emphasized.

Distribution and diversity of type VI secretion system clusters in Enterobacter bugandensis and Enterobacter cloacae

Gram-negative bacteria use type VI secretion systems (T6SSs) to antagonize neighbouring cells. Although primarily involved in bacterial competition, the T6SS is also implicated in pathogenesis, biofilm formation and ion scavenging. Enterobacter species belong to the ESKAPE pathogens, and while their antibiotic resistance has been well studied, less is known about their pathogenesis. Here, we investigated the distribution and diversity of T6SS components in isolates of two clinically relevant Enterobacter species, E. cloacae and E. bugandensis. T6SS clusters are grouped into four types (T6SSi-T6SSiv), of which type i can be further divided into six subtypes (i1, i2, i3, i4a, i4b, i5). Analysis of a curated dataset of 31 strains demonstrated that most of them encode T6SS clusters belonging to the T6SSi type. All T6SS-positive strains possessed a conserved i3 cluster, and many harboured one or two additional i2 clusters. These clusters were less conserved, and some strains displayed evidence of deletion. We focused on a pathogenic E. bugandensis clinical isolate for comprehensive in silico effector prediction, with comparative analyses across the 31 isolates. Several new effector candidates were identified, including an evolved VgrG with a metallopeptidase domain and a Tse6-like protein. Additional effectors included an anti-eukaryotic catalase (KatN), M23 peptidase, PAAR and VgrG proteins. Our findings highlight the diversity of Enterobacter T6SSs and reveal new putative effectors that may be important for the interaction of these species with neighbouring cells and their environment.

Population genomic analysis of clinical ST15 Klebsiella pneumoniae strains in China

ST15 Klebsiella pneumoniae (Kpn) is a growing public health concern in China and worldwide, yet its genomic and evolutionary dynamics in this region remain poorly understood. This study comprehensively elucidates the population genomics of ST15 Kpn in China by analyzing 287 publicly available genomes. The proportion of the genomes increased sharply from 2012 to 2021, and 92.3% of them were collected from the Yangtze River Delta (YRD) region of eastern China. Carbapenemase genes, including OXA-232, KPC-2, and NDM, were detected in 91.6% of the studied genomes, and 69.2% of which were multidrug resistant (MDR) and hypervirulent (hv). Phylogenetic analysis revealed four clades, C1 (KL112, 59.2%), C2 (mainly KL19, 30.7%), C3 (KL48, 0.7%) and C4 (KL24, 9.4%). C1 appeared in 2007 and was OXA-232-producing and hv; C2 and C4 appeared between 2005 and 2007, and both were KPC-2-producing but with different levels of virulence. Transmission clustering detected 86.1% (n = 247) of the enrolled strains were grouped into 55 clusters (2-159 strains) and C1 was more transmissible than others. Plasmid profiling revealed 88 plasmid clusters (PCs) that were highly heterogeneous both between and within clades. 60.2% (n = 53) of the PCs carrying AMR genes and 7 of which also harbored VFs. KPC-2, NDM and OXA-232 were distributed across 14, 4 and 1 PCs, respectively. The MDR-hv strains all carried one of two homologous PCs encoding iucABCD and rmpA2 genes. Pangenome analysis revealed two major coinciding accessory components predominantly located on plasmids. One component, associated with KPC-2, encompassed 15 additional AMR genes, while the other, linked to OXA-232, involved seven more AMR genes. This study provides essential insights into the genomic evolution of the high-risk ST15 CP-Kpn strains in China and warrants rigorous monitoring.

Predicting Human Risk with Multidrug Resistant Enterobacter hormaechei MS2 having MCR 9 Gene Isolated from the Feces of Healthy Broiler Through Whole-Genome Sequence-Based Analysis

The zoonotic spread of antimicrobial resistance (AMR) and the associated infections are becoming a major threat to the human population worldwide. Strategies to identify the potential pathogen dissemination by seemingly healthy livestock are at a nascent stage and it is of significant importance to monitor environmental evolution of AMR. In this study, a multidrug resistant strain (MDR) of Enterobacter hormaechei MS2 isolated from the feces of healthy broiler chicken has been characterized by whole-genome sequencing-based method. Here, the isolate was primarily subjected to antimicrobial susceptibility testing followed genome sequencing and analysis. From the antimicrobial susceptibility testing result, the strain was found to be resistant to multiple classes of drugs including the colistin which is an important  last resort drug used to treat infectious diseases. The resistome prediction of genomic data further revealed the presence of 7 perfect and 26 strict hits including those for MCR-9 and FosA2. The pathogenicity prediction has also demonstrated the strain to have the potential to be a human pathogen with 0.72 probability. The phylogenetic analysis has also supported the zoonotic potential of the strain due to its clustering with isolates from both human and livestock-associated host groups. The results of the study suggest the need for a strong surveillance system to identify the opportunistic zoonotic pathogens to prevent a silent AMR menace mediated by them. Carriage of multi-drug resistant strains in the livestock gut microbiome is also a serious concern as it has high AMR transmissibility through contact and supply chain activities.

The CARBA-MAP study: national mapping of carbapenemases in Spain (2014-2018)

Introduction

Infections caused by carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa, including isolates producing acquired carbapenemases, constitute a prevalent health problem worldwide. The primary objective of this study was to determine the distribution of the different carbapenemases among carbapenemase-producing Enterobacterales (CPE, specifically Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae complex, and Klebsiella aerogenes) and carbapenemase-producing P. aeruginosa (CPPA) in Spain from January 2014 to December 2018.

Methods

A national, retrospective, cross-sectional multicenter study was performed. The study included the first isolate per patient and year obtained from clinical samples and obtained for diagnosis of infection in hospitalized patients. A structured questionnaire was completed by the participating centers using the REDCap platform, and results were analyzed using IBM SPSS Statistics 29.0.0.

Results

A total of 2,704 carbapenemase-producing microorganisms were included, for which the type of carbapenemase was determined in 2692 cases: 2280 CPE (84.7%) and 412 CPPA (15.3%), most often using molecular methods and immunochromatographic assays. Globally, the most frequent types of carbapenemase in Enterobacterales and P. aeruginosa were OXA-48-like, alone or in combination with other enzymes (1,523 cases, 66.8%) and VIM (365 cases, 88.6%), respectively. Among Enterobacterales, carbapenemase-producing K. pneumoniae was reported in 1821 cases (79.9%), followed by E. cloacae complex in 334 cases (14.6%). In Enterobacterales, KPC is mainly present in the South and South-East regions of Spain and OXA-48-like in the rest of the country. Regarding P. aeruginosa, VIM is widely distributed all over the country. Globally, an increasing percentage of OXA-48-like enzymes was observed from 2014 to 2017. KPC enzymes were more frequent in 2017-2018 compared to 2014-2016.

Discussion

Data from this study help to understand the situation and evolution of the main species of CPE and CPPA in Spain, with practical implications for control and optimal treatment of infections caused by these multi-drug resistant organisms.

Genomic characterisation of a blaKPC-2- and mcr-10-co-harbouring Enterobacter kobei isolate with high-level resistance to colistin and carbapenems

OBJECTIVES

The emergence and spread of colistin resistance in carbapenem-resistant Enterobacteriaceae pose a serious threat to human and animal health. This work aimed to characterise the genetic features of antimicrobial resistance of the carbapenem- and colistin-resistant Enterobacter kobei strain SCLZS19, isolated from hospital sewage, by using whole genome sequencing.

METHODS

Antimicrobial susceptibility tests were performed using the disk diffusion method. Whole genome sequencing of SCLZS19 was carried out on the HiSeq 2000 combined with PacBio RSII platforms. Sequence type, plasmid incompatibility types, resistance genes, and insertion elements were identified using multilocus sequence typing, PlasmidFinder, ResFinder, and ISfinder, respectively. Conjugation assays were performed using both broth- and filter-based methods with the azide-resistant Escherichia coli J53 as the recipient. The function of the mcr-9-like variant was determined by gene cloning.

RESULTS

E. kobei SCLZS19 had a 4 862 177-bp circular chromosome and nine circular plasmids ranging in size from 4120 bp to 282 472 bp. It carried 11 antibiotic resistance genes, and 10 of them were located on plasmids. The colistin resistance gene mcr-10 was located on a 118 766-bp non-transferable IncF (Y3:A-:B-) plasmid. The carbapenemase gene blaKPC-2 was carried by a self-transmissible IncP6 plasmid, which is epidemic in China. In addition, SCLZS19 also carried an mcr-9-like variant on a IncHI2 (ST1) plasmid. The cloning assay showed that the mcr-9-like variant did not mediate colistin resistance in E. coli DH5α.

CONCLUSION

The findings highlight that carbapenem- and colistin-resistant Enterobacterales from water environments may serve as a reservoir for clinically significant antibiotic resistance genes, and continuous surveillance is required.

Outbreak of OXA-232-producing carbapenem-resistant Klebsiella pneumoniae ST15 in a Chinese teaching hospital: a molecular epidemiological study

Background and Aims

The incidence of OXA-232-producing carbapenem-resistant Klebsiella pneumoniae (CRKP) has been on the rise in China over the past five years, potentially leading to nosocomial epidemics. This study investigates the first outbreak of CRKP in the Second Affiliated Hospital of Jiaxing University.

Methods

Between February 2021 and March 2022, 21 clinical isolates of OXA-232-producing CRKP were recovered from 16 patients in the Second Affiliated Hospital of Jiaxing University. We conducted antimicrobial susceptibility tests, whole genome sequencing, and bioinformatics to determine the drug resistance profile of these clinical isolates.

Results

Whole-genome sequencing revealed that all 21 OXA-232-producing CRKP strains belonged to the sequence type 15 (ST15) and shared similar resistance, virulence genes, and plasmid types, suggesting clonal transmission between the environment and patients. Integrated genomic and epidemiological analysis traced the outbreak to two clonal transmission clusters, cluster 1 and cluster 2, including 14 and 2 patients. It was speculated that the CRKP transmission mainly occurred in the ICU, followed by brain surgery, neurosurgery, and rehabilitation department. Phylogenetic analysis indicated that the earliest outbreak might have started at least a year before the admission of the index patient, and these strains were closely related to those previously isolated from two major adjacent cities, Shanghai and Hangzhou. Comparative genomics showed that the IncFII-type and IncHI1B-type plasmids of cluster 2 had homologous recombination at the insertion sequence sites compared with the same type of plasmids in cluster 1, resulting in the insertion of 4 new drug resistance genes, including TEM-1, APH(6)-Id, APH(3'')-Ib and sul2.

Conclusions

Our study observed the clonal spread of ST15 OXA-232-producing between patients and the hospital environment. The integration of genomic and epidemiological data offers valuable insights and facilitate the control of nosocomial transmission.

Molecular characterization and in-depth genome analysis of Enterobacter sp. S-16

Enterobacter species are considered to be an opportunistic human pathogen owing to the existence of antibiotic-resistant strains and drug resides; however, the detailed analysis of the antibiotic resistance and virulence features in environmental isolates is poorly characterized. Here, in the study, we characterized the biochemical characteristics, and genome, pan-genome, and comparative genome analyses of an environmental isolate Enterobacter sp. S-16. The strain was identified as Enterobacter spp. by using 16S rRNA gene sequencing. To unravel genomic features, whole genome of Enterobacter sp. S-16 was sequenced using a hybrid assembly approach and genome assembly was performed using the Unicycler tool. The assembled genome contained the single conting size 5.3 Mbp, GC content 55.43%, and 4500 protein-coding genes. The genome analysis revealed the various gene clusters associated with virulence, antibiotic resistance, type VI secretion system (T6SS), and many stress tolerant genes, which may provide important insight for adapting to changing environment conditions. Moreover, different metabolic pathways were identified that potentially contribute to environmental survival. Various hydrolytic enzymes and motility functions equipped the strain S-16 as an active colonizer. The genome analysis confirms the presence of carbohydrate-active enzymes (CAZymes), and non-enzymatic carbohydrate-binding modules (CBMs) involved in the hydrolysis of complex carbohydrate polymers. Moreover, the pan-genome analysis provides detailed information about the core genes and shared genes with the closest related Enterobacter species. The present study is the first report showing the presence of YdhE/NorM in Enterobacter spp. Thus, the elucidation of genome sequencing will increase our understanding of the pathogenic nature of environmental isolate, supporting the One Health Concept.

Resistance to aztreonam-avibactam due to a mutation of SHV-12 in Enterobacter

Aztreonam-avibactam is an important option against Enterobacterales producing metallo-β-lactamases (MBLs). We obtained an aztreonam-avibactam-resistant mutant of an MBL-producing Enterobacter mori strain by induced mutagenesis. Genome sequencing revealed an Arg244Gly (Ambler position) substitution of SHV-12 β-lactamase in the mutant. Cloning and susceptibility testing verified that the SHV-12 Arg244Gly substitution led to significantly reduced susceptibility to aztreonam-avibactam (MIC, from 0.5/4 to 4/4 mg/L) but with the loss of resistance to cephalosporins as tradeoff. Arg244 of SHV involves in the binding of avibactam by forming an arginine-mediated salt bridge and is a critical residue to interact with β-lactams. Molecular modeling analysis demonstrated that the Arg244Gly substitution hindered the binding of avibactam to SHV with higher binding energy (from - 5.24 to -4.32 kcal/mol) and elevated inhibition constant Ki (from 143.96 to 677.37 µM) to indicate lower affinity. This substitution, however, resulted in loss of resistance to cephalosporins as tradeoff by impairing substrate binding. This represents a new aztreonam-avibactam resistance mechanism.

Enterobacter pseudoroggenkampii sp. nov. carrying quinolone-resistant gene qnrE recovered from clinical samples in China

Two Enterobacter strains 155092^T and 170,225 were isolated from clinical samples, pus and sputum, from two hospitalised patients separately, in China. Preliminary identification using Vitek II microbiology system assigned the strains to the Enterobacter cloacae complex. The two strains were subjected to genome sequencing and genome-based taxonomy analysis with type strains of all Enterobacter species and those within closely related genera Huaxiibacter, Leclercia, Lelliottia, and Pseudoenterobacter. The average nucleotide identity (ANI) and in silico DNA-DNA hybridisation (isDDH) values between the two strains were 98.35% and 89.4%, respectively, suggesting that they belong to one species. The two strains had the highest ANI (95.02% and 95.04%) with the type strain of Enterobacter quasiroggenkampii. Their highest isDDH values, also seen with the type strain of E. quasiroggenkampii, were 59.5% and 59.8%, well below the 70% cutoff to define species. The two strains were also characterised for morphological and biochemical features by a set of experiments and observations. The abilities of metabolising gelatin and L-rhamnose could differentiate the two strains from all currently known Enterobacter species. Collectively, the two strains represent a novel Enterobacter species, for which we propose Enterobacter pseudoroggenkampii sp. nov. as the species name. The type strain of this novel species is155092^T (= GDMCC 1.3415^T = JCM 35646^T). The two strains also carried multiple virulence factors comprising aerobactin-encoding iucABCD-iutA and salmochelin-encoding iroN. The two strains also had chromosomally located qnrE, a gene associated with reduced susceptibility to quinolones, suggesting that this species is a potential reservoir of qnrE genes.

Cloacaenodin, an Antimicrobial Lasso Peptide with Activity against Enterobacter

Using genome mining and heterologous expression, we report the discovery and production of a new antimicrobial lasso peptide from species related to the Enterobacter cloacae complex. Using NMR and mass spectrometric analysis, we show that this lasso peptide, named cloacaenodin, employs a threaded lasso fold which imparts proteolytic resistance that its unthreaded counterpart lacks. Cloacaenodin has selective, low micromolar, antimicrobial activity against species related to the E. cloacae complex, including species implicated in nosocomial infections and against clinical isolates of carbapenem-resistant Enterobacterales. We further used site-directed mutagenesis to probe the importance of specific residues to the peptide's biosynthesis, stability, and bioactivity.

Polygonatum sibiricum saponin Exerts Beneficial Hypoglycemic Effects in Type 2 Diabetes Mice by Improving Hepatic Insulin Resistance and Glycogen Synthesis-Related Proteins

Type 2 diabetes mellitus (T2DM) is a systemic metabolic disorder characterized by insulin deficiency and insulin resistance. Recently, it has become a significant threat to public health. Polygonatum sibiricum saponin (PSS) has potential hypoglycemic effects, but its specific mechanism needs further study. In this study, PSS significantly decreased the level of blood glucose, water intake, and the organ index in diabetic mice. Meanwhile, PSS effectively reduced the content of total triglyceride (TG), total cholesterol (TCHO), low-density lipoprotein cholesterol (LDL-C), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) in the blood, and increased the content of high-density lipoprotein cholesterol (HDL-C). This suggests that PSS could reduce the content of blood lipids and initially improve the damage of hepatocytes. We found that PSS alleviated hepatic insulin resistance, repaired islet beta cells, and enabled insulin to play its biological role normally. It also improved oral glucose tolerance and abated serum lipopolysaccharide (LPS) and glycosylated hemoglobin (HbA1c) levels in T2DM mice. Furthermore, studies have found that PSS increased the content of phosphorylated protein kinase B (AKT), thereby promoting the effect of glucose transporter 4 (GLUT-4), and activating glycogen synthase kinase 3beta (GSK-3β) and glycogen synthase (GS) proteins to promote hepatic glycogen synthesis. Finally, we found that PSS could promote the growth of beneficial bacteria such as Bifidobacterium and Lactobacillus, reduce the growth of harmful bacteria such as Enterococcus and Enterobacter, and preliminarily improve the composition of important bacteria in the intestine. These studies indicate that PSS has an excellent hypoglycemic effect, which provides a potential new treatment for T2DM and guidance for more in-depth research.

Emergence of a Novel Lineage and Wide Spread of a blaCTX-M-15/IncHI2/ST1 Plasmid among Nosocomial Enterobacter in Guadeloupe

Between April 2018 and August 2019, a total of 135 strains of Enterobacter cloacae complex (ECC) were randomly collected at the University Hospital Center of Guadeloupe to investigate the structure and diversity of the local bacterial population. These nosocomial isolates were initially identified genetically by the hsp60 typing method, which revealed the clinical relevance of E. xiangfangensis (n = 69). Overall, 57/94 of the third cephalosporin-resistant strains were characterized as extended-spectrum-β-lactamase (ESBL) producers, and their whole-genome was sequenced using Illumina technology to determine the clonal relatedness and diffusion of resistance genes. We found limited genetic diversity among sequence types (STs). ST114 (n = 13), ST1503 (n = 9), ST53 (n = 5) and ST113 (n = 4), which belong to three different Enterobacter species, were the most prevalent among the 57 ESBL producers. The blaCTXM-15 gene was the most prevalent ESBL determinant (56/57) and was in most cases associated with IncHI2/ST1 plasmid replicon carriage (36/57). To fully characterize this predominant blaCTXM-15/IncHI2/ST1 plasmid, four isolates from different lineages were also sequenced using Oxford Nanopore sequencing technology to generate long-reads. Hybrid sequence analyses confirmed the circulation of a well-conserved plasmid among ECC members. In addition, the novel ST1503 and its associated species (ECC taxon 4) were analyzed, in view of its high prevalence in nosocomial infections. These genetic observations confirmed the overall incidence of nosocomial ESBL Enterobacteriaceae infections acquired in this hospital during the study period, which was clearly higher in Guadeloupe (1.59/1000 hospitalization days) than in mainland France (0.52/1,000 hospitalization days). This project revealed issues and future challenges for the management and surveillance of nosocomial and multidrug-resistant Enterobacter in the Caribbean.

Depletion of Gut Microbiota Inhibits Hepatic Lipid Accumulation in High-Fat Diet-Fed Mice

Dysregulated lipid metabolism is a key pathology in metabolic diseases and the liver is a critical organ for lipid metabolism. The gut microbiota has been shown to regulate hepatic lipid metabolism in the host. However, the underlying mechanism by which the gut microbiota influences hepatic lipid metabolism has not been elucidated. Here, a gut microbiota depletion mouse model was constructed with an antibiotics cocktail (Abx) to study the mechanism through which intestinal microbiota regulates hepatic lipid metabolism in high-fat diet (HFD)-fed mice. Our results showed that the Abx treatment effectively eradicated the gut microbiota in these mice. Microbiota depletion reduced the body weight and fat deposition both in white adipose tissue and liver. In addition, microbiota depletion reduced serum levels of glucose, total cholesterol (TC), low-density lipoproteins (LDL), insulin, and leptin in HFD-fed mice. Importantly, the depletion of gut microbiota in HFD-fed mice inhibited excessive hepatic lipid accumulation. Mechanistically, RNA-seq results revealed that gut microbiota depletion changed the expression of hepatic genes involved in cholesterol and fatty acid metabolism, such as Cd36, Mogat1, Cyp39a1, Abcc3, and Gpat3. Moreover, gut microbiota depletion reduced the abundance of bacteria associated with abnormal metabolism and inflammation, including Lachnospiraceae, Coriobacteriaceae_UCG-002, Enterorhabdus, Faecalibaculum, and Desulfovibrio. Correlation analysis showed that there was strong association between the altered gut microbiota abundance and the serum cholesterol level. This study indicates that gut microbiota ameliorates HFD-induced hepatic lipid metabolic dysfunction, which might be associated with genes participating in cholesterol and fatty acid metabolism in the liver.

Antibacterial pyrazoles: tackling resistant bacteria

Bacterial resistance to antibiotics threatens our progress in healthcare, modern medicine, food production and ultimately life expectancy. Antibiotic resistance is a global concern, which spreads rapidly across borders and continents due to rapid travel of people, animals and goods. Derivatives of metabolically stable pyrazole nucleus are known for their wide range of pharmacological properties, including antibacterial activities. This review highlights recent reports of pyrazole derivatives targeting different bacterial strains focusing on the drug-resistant variants. Pyrazole derivatives target different metabolic pathways of both Gram-positive and Gram-negative bacteria.

Polymyxin and lipopeptide antibiotics: membrane-targeting drugs of last resort

The polymyxin and lipopeptide classes of antibiotics are membrane-targeting drugs of last resort used to treat infections caused by multi-drug-resistant pathogens. Despite similar structures, these two antibiotic classes have distinct modes of action and clinical uses. The polymyxins target lipopolysaccharide in the membranes of most Gram-negative species and are often used to treat infections caused by carbapenem-resistant species such as Escherichia coli, Acinetobacter baumannii and Pseudomonas aeruginosa. By contrast, the lipopeptide daptomycin requires membrane phosphatidylglycerol for activity and is only used to treat infections caused by drug-resistant Gram-positive bacteria such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. However, despite having distinct targets, both antibiotic classes cause membrane disruption, are potently bactericidal in vitro and share similarities in resistance mechanisms. Furthermore, there are concerns about the efficacy of these antibiotics, and there is increasing interest in using both polymyxins and daptomycin in combination therapies to improve patient outcomes. In this review article, we will explore what is known about these distinct but structurally similar classes of antibiotics, discuss recent advances in the field and highlight remaining gaps in our knowledge.

Re-examining the association of AmpC variants with Enterobacter species in the context of updated taxonomy

We performed whole genome sequencing for 17 Enterobacter clinical strains and analyzed all available Enterobacter genomes and its closely-related genera (n=3,389) from NCBI. The exact origin of plasmid-borne bla_CMH and bla_MIR genes is Enterobacter cloacae and Enterobacter roggenkampii, respectively, while plasmid-borne bla_ACT genes originated from multiple other Enterobacter species including Enterobacter xiangfangensis, Enterobacter hoffmannii, and Enterobacter asburiae, Enterobacter ludwigii, and Enterobacter kobei. The genus of Enterobacter represents a large reservoir of plasmid-borne AmpC β-lactamase.

Putative mobilized colistin resistance genes in the human gut microbiome

BACKGROUND

The high incidence of bacterial genes that confer resistance to last-resort antibiotics, such as colistin, caused by mobilized colistin resistance (mcr) genes, poses an unprecedented threat to human health. Understanding the spread, evolution, and distribution of such genes among human populations will help in the development of strategies to diminish their occurrence. To tackle this problem, we investigated the distribution and prevalence of potential mcr genes in the human gut microbiome using a set of bioinformatics tools to screen the Unified Human Gastrointestinal Genome (UHGG) collection for the presence, synteny and phylogeny of putative mcr genes, and co-located antibiotic resistance genes.

RESULTS

A total of 2079 antibiotic resistance genes (ARGs) were classified as mcr genes in 2046 metagenome assembled genomes (MAGs), distributed across 1596 individuals from 41 countries, of which 215 were identified in plasmidial contigs. The genera that presented the largest number of mcr-like genes were Suterella and Parasuterella. Other potential pathogens carrying mcr genes belonged to the genus Vibrio, Escherichia and Campylobacter. Finally, we identified a total of 22,746 ARGs belonging to 21 different classes in the same 2046 MAGs, suggesting multi-resistance potential in the corresponding bacterial strains, increasing the concern of ARGs impact in the clinical settings.

CONCLUSION

This study uncovers the diversity of mcr-like genes in the human gut microbiome. We demonstrated the cosmopolitan distribution of these genes in individuals worldwide and the co-presence of other antibiotic resistance genes, including Extended-spectrum Beta-Lactamases (ESBL). Also, we described mcr-like genes fused to a PAP2-like domain in S. wadsworthensis. These novel sequences increase our knowledge about the diversity and evolution of mcr-like genes. Future research should focus on activity, genetic mobility and a potential colistin resistance in the corresponding strains to experimentally validate those findings.