Transmissible ST3-IncHI2 Plasmids Are Predominant Carriers of Diverse Complex IS26-Class 1 Integron Arrangements in Multidrug-Resistant Salmonella

Multidrug resistance in Salmonella isolates of swine origin: mobile genetic elements and plasmids associated with cephalosporin resistance with potential transmission to humans

The emergence of foodborne Salmonella strains carrying antimicrobial resistance (AMR) in mobile genetic elements (MGE) is a significant public health threat in a One Health context requiring continuous surveillance. Resistance to ciprofloxacin and cephalosporins is of particular concern. Since pigs are a relevant source of foodborne Salmonella for human beings, we studied transmissible AMR genes and MGE in a collection of 83 strains showing 9 different serovars and 15 patterns of multidrug resistant (MDR) previously isolated from pigs raised in the conventional breeding system of Northern Spain. All isolates were susceptible to ciprofloxacin and three isolates carried blaCMY-2 or blaCTX-M-9 genes responsible for cefotaxime resistance. Filter mating experiments showed that the two plasmids carrying blaCTX-M-9 were conjugative while that carrying blaCMY-2 was self-transmissible by transformation. Whole-genome sequencing and comparative analyses were performed on the isolates and plasmids. The IncC plasmid pSB109, carrying blaCMY-2, was similar to one found in S. Reading from cattle, indicating potential horizontal transfer between serovars and animal sources. The IncHI2 plasmids pSH102 in S. Heidelberg and pSTM45 in S. Typhimurium ST34, carrying blaCTX-M-9, shared similar backbones and two novel "complex class 1 integrons" containing different AMR and heavy metal genes. Our findings emphasize the importance of sequencing techniques to identify emerging AMR regions in conjugative and stable plasmids from livestock production. The presence of MGE carrying clinically relevant AMR genes raises public health concerns, requiring monitoring to mitigate the emergence of bacteria carrying AMR genes and subsequent spread through animals and food.IMPORTANCEThe emergence of foodborne Salmonella strains carrying antimicrobial resistance (AMR) in mobile genetic elements (MGE) is a significant public health threat in a One Health context. Since pigs are a relevant source of foodborne Salmonella for humans, in this study, we investigate different aspects of AMR in a collection of 83 Salmonella showing nine different serovars and 15 patterns of multidrug resistant (MDR) isolated from pigs raised in the conventional breeding system. Our findings emphasize the importance of sequencing techniques to identify emerging AMR regions in conjugative and stable plasmids from livestock production. The presence of MGE carrying clinically relevant AMR genes raises public health concerns, requiring monitoring to mitigate the emergence of bacteria carrying AMR genes and subsequent spread through animals and food.

Genotypic analyses of IncHI2 plasmids from enteric bacteria

Incompatibility (Inc) HI2 plasmids are large (typically > 200 kb), transmissible plasmids that encode antimicrobial resistance (AMR), heavy metal resistance (HMR) and disinfectants/biocide resistance (DBR). To better understand the distribution and diversity of resistance-encoding genes among IncHI2 plasmids, computational approaches were used to evaluate resistance and transfer-associated genes among the plasmids. Complete IncHI2 plasmid (N = 667) sequences were extracted from GenBank and analyzed using AMRFinderPlus, IntegronFinder and Plasmid Transfer Factor database. The most common IncHI2-carrying genera included Enterobacter (N = 209), Escherichia (N = 208), and Salmonella (N = 204). Resistance genes distribution was diverse, with plasmids from Escherichia and Salmonella showing general similarity in comparison to Enterobacter and other taxa, which grouped together. Plasmids from Enterobacter and other taxa had a higher prevalence of multiple mercury resistance genes and arsenic resistance gene, arsC, compared to Escherichia and Salmonella. For sulfonamide resistance, sul1 was more common among Enterobacter and other taxa, compared to sul2 and sul3 for Escherichia and Salmonella. Similar gene diversity trends were also observed for tetracyclines, quinolones, β-lactams, and colistin. Over 99% of plasmids carried at least 25 IncHI2-associated conjugal transfer genes. These findings highlight the diversity and dissemination potential for resistance across different enteric bacteria and value of computational-based approaches for the resistance-gene assessment.

Snapshot of resistome, virulome and mobilome in aquaculture

Aquaculture environments can be hotspots for resistance genes through the surrounding environment. Our objective was to study the resistome, virulome and mobilome of Gram-negative bacteria isolated in seabream and bivalve molluscs, using a WGS approach. Sixty-six Gram-negative strains (Aeromonadaceae, Enterobacteriaceae, Hafniaceae, Morganellaceae, Pseudomonadaceae, Shewanellaceae, Vibrionaceae, and Yersiniaceae families) were selected for genomic characterization. The species and MLST were determined, and antibiotic/disinfectants/heavy metals resistance genes, virulence determinants, MGE, and pathogenicity to humans were investigated. Our study revealed new sequence-types (e.g. Aeromonas spp. ST879, ST880, ST881, ST882, ST883, ST887, ST888; Shewanella spp. ST40, ST57, ST58, ST60, ST61, ST62; Vibrio spp. ST206, ST205). >140 different genes were identified in the resistome of seabream and bivalve molluscs, encompassing genes associated with β-lactams, tetracyclines, aminoglycosides, quinolones, sulfonamides, trimethoprim, phenicols, macrolides and fosfomycin resistance. Disinfectant resistance genes qacE-type, sitABCD-type and formA-type were found. Heavy metals resistance genes mdt, acr and sil stood out as the most frequent. Most resistance genes were associated with antibiotics/disinfectants/heavy metals commonly used in aquaculture settings. We also identified 25 different genes related with increased virulence, namely associated with adherence, colonization, toxins production, red blood cell lysis, iron metabolism, escape from the immune system of the host. Furthermore, 74.2 % of the strains analysed were considered pathogenic to humans. We investigated the genetic environment of several antibiotic resistance genes, including blaTEM-1B, blaFOX-18, aph(3″)-Ib, dfrA-type, aadA1, catA1-type, tet(A)/(E), qnrB19 and sul1/2. Our analysis also focused on identifying MGE in proximity to these genes (e.g. IntI1, plasmids and TnAs), which could potentially facilitate the spread of resistance among bacteria across different environments. This study provides a comprehensive examination of the diversity of resistance genes that can be transferred to both humans and the environment, with the recognition that aquaculture and the broader environment play crucial roles as intermediaries within this complex transmission network.

Class 1 integron carrying qacEΔ1 gene confers resistance to disinfectant and antibiotics in Salmonella

Salmonella has presented increasingly alarming rates of antimicrobial resistance believed to be a result of a high prevalence of integrons. It is speculated that disinfectant-resistant isolates are due to the expression of qacEΔ1, an efflux pump located in the 3' conserved sequence (3'CS) of class 1 integrons. With this concern, we tested the antibiotic and disinfectant resistance of 581 Salmonella strains collected from different sources, and characterized their integron structures. Gene expression and induction experiments were also performed. Results showed that Salmonella have high resistance to antimicrobials, especially to sulfonamides (SAs, 78.83 %), tetracyclines (TCs, 75.04 %) and benzalkonium chloride (BC, 87.26 %). The multi-drug resistance (MDR) frequency reached up to 63.17 %, and the prevalence of intI1 was 45.78 %. Molecular characterization of class 1 integrons exhibited nine different gene cassette arrays, of these, dfrA12-orf-aadA2 (n = 75), EstX (n = 25) and aadA2 (n = 14) were the most frequent. Importantly, 74.06 % of intI1-positive isolates were carrying qacEΔ1-sul1 genes in the 3'CS. This study also demonstrated that phenotypic resistance to both antibiotics and disinfectants was significantly correlated with the emergence of intI1 (p < 0.05). 91.37 % of qacEΔ1-sul1 positive Salmonella were found with disinfectant resistance. Additionally, expression of qacEΔ1 gene in Escherichia coli confirmed qacEΔ1 is predominantly involved in conferring disinfectant resistance. Disinfectant induction experiments further implicated qacEΔ1 in disinfectant resistance. RT-qPCR revealed a disinfectant-mediated increase in the relative expression of antibiotic-resistant genes (ARGs), aadA2 and dfrA12 on the integron, and efflux pump genes (mdtH and acrD) indicating that disinfectant could trigger co or cross-resistance. Therefore, our study confirmed that using disinfectant could provide selection pressure for strains with acquired resistance to antibiotics, providing new insights into the public health impact of Salmonella and guide continued efforts in antimicrobial stewardship and prevention of antibiotic resistance.

High rate of multidrug resistance and integrons in Escherichia coli isolates from diseased ducks in select regions of China

With the increasing number of ducks being raised and consumed, it is crucial to monitor the presence of multidrug resistant (MDR) bacteria in duck farming. Waterfowl, such as ducks, can contribute to the rapid dissemination of antibiotic resistance genes (ARGs). The objective of this study was to investigate the antimicrobial resistance (AMR), ARGs, and mobile genetic elements (MGEs), such as IS26, tbrC, ISEcp1 in Escherichia coli(E. coli) isolated from the intestinal contents of diseased ducks between 2021 and 2022 in Sichuan, Chongqing and Anhui, China. The AMR phenotypes of 201 isolated E. coli strains were determined using the minimum inhibitory concentrations (MICs) method. Subsequently, polymerase chain reaction and sequencing techniques were employed to screen for integron-integrase genes (intI1, intI2, intI3 genes), gene cassettes (GCs), MGEs, and ARGs. The results demonstrated that 96.5% of the E. coli isolates were resistant to at least 1 antibiotic, with 88.1% of the strains displaying MDR phenotype. The highest AMR phenotype observed was for trimethoprim-sulfamethoxazole (88.1%). Furthermore, class 1 and class 2 integrons were detected in 68.2% and 3.0% of all the isolates, respectively, whereas no class 3 integrons were found. Ten types of GCs were identified in the variable regions of class 1 and class 2 integrons. Moreover, 10 MGEs were observed in 46 combinations, with IS26 exhibiting the highest detection rate (89.6%). Among the 22 types of ARGs, tetA (77.1%) was the most frequently detected. In the conjugational transfer experiment, transconjugants were found to carry specific ARGs and MGEs, with their MIC values were significantly higher than those of recipient E. coli J53, indicating their status as MDR bacteria. This study emphasizes the necessity of monitoring MGEs, ARGs, and integrons in duck farms. It provides valuable insights into the complex formation mechanisms of AMR and may aid in preventing and controlling the spread of MDR bacteria in waterfowl breeding farm.

Prevalence and molecular characterization of mcr-1-positive foodborne ST34-Salmonella isolates in China

Salmonella enterica serovar Typhimurium (S. Typhimurium) and S. 4,[5],12:i:- have become the most common serovars associated with human salmonellosis worldwide. Moreover, the emergence of mcr-carrying S. Typhimurium and S. 4,[5],12:i:- with multidrug resistance (MDR) patterns has posed a threat to public health. In this study, we retrospectively screened 2009-2022 laboratory-preserved strains for the presence of mcr genes. We obtained 16 mcr-1-positive S. Typhimurium and S. 4,[5],12:i:- strains with MDR that belonged to sequence type 34 (ST34). Whole-genome sequencing analysis revealed that the mcr-1 was located on the IncI2 or IncHI2 plasmids. The ISApl1 element downstream of mcr-1 was present in all pig-derived strains. Conjugation experiments confirmed that nine mcr-1-carrying IncHI2 plasmids could not be transferred to Escherichia coli due to loss of the conjugation region. Finally, core genome single nucleotide polymorphism (cgSNP) analyses of the 16 mcr-1-carrying strains and 77 mcr-carrying ST34-Salmonella genome sequences from the NCBI and ENA databases showed that five out of eight clusters contained strains from pig and pig products, revealing pigs and pig products as key reservoirs of mcr-1-positive ST34-Salmonella strains. The transmission of mcr-carrying ST34 Salmonella strains to humans via the pig food chain is a potential cause for public health concern in controlling human salmonellosis.

Whole Genome Sequencing Reveals Presence of High-Risk Global Clones of Klebsiella pneumoniae Harboring Multiple Antibiotic Resistance Genes in Multiple Plasmids in Mwanza, Tanzania

BACKGROUND

Klebsiella pneumoniae is an important multidrug-resistant (MDR) pathogen, causing both community- and healthcare-associated infections. The resistance is due to the continuous accumulation of multiple antibiotic-resistance-genes (ARGs) through spontaneous genomic mutations and the acquisition of conjugative plasmids. This study presents antibiotics resistance genes, plasmids replicons, and virulence genes of K. pneumoniae isolates from clinical specimens in a tertiary hospital, Mwanza, Tanzania.

METHODS

Whole genome sequencing (WGS) of 34 K. pneumoniae was performed, using an Illumina NextSeq 500, followed by in silco analysis.

RESULTS

A total of 34 extended-spectrum beta-lactamase-producing K. pneumoniae, isolated from blood samples from neonatal units were whole-genome sequenced. Of these, 28 (82.4%) had an identified sequence type (ST), with ST14 (39.3%, n = 11) being frequently identified. Moreover, 18 (52.9%) of the bacteria harbored at least one plasmid, from which a total of 25 plasmid replicons were identified with a predominance of IncFIB(K) 48.0% (n = 12). Out of 34 sequenced K. pneumoniae, 32 (94.1%) were harboring acquired antibiotic/biocides-resistance-genes (ARGs) with a predominance of bla_CTX-M-15 (90.6%), followed by oqxB (87.5%), oqxA (84.4%), bla_TEM-1B (84.4%) and sul2 (84.4%). Interestingly, we observed the ColRNAI plasmid-replicon (n = 1) and qacE gene (n = 4) for the first time in this setting.

CONCLUSION

Global high-risk clones of K. pneumoniae isolates carry multiple ARGs in multiple plasmid-replicons. Findings from this study warrant genomic-based surveillance to monitor high-risk global clones, epidemic plasmids and ARGs in low- and middle-income countries.

Population analysis of heavy metal and biocide resistance genes in Salmonella enterica from human clinical cases in New Hampshire, United States

Microbes frequently encounter heavy metals and other toxic compounds generated from natural biogeochemical processes and anthropogenic activities. Here, we analyzed the prevalence and association of genes conferring resistance to heavy metals, biocides, and antimicrobial compounds in 394 genome sequences of clinical human-derived S. enterica from New Hampshire, USA. The most prevalent was the gold operon (gesABC-golTSB), which was present in 99.2% of the genomes. In contrast, the other five heavy metal operons (arsenic, copper, mercury, silver, tellurite) were present in 0.76% (3/394)–5.58% (22/394) of the total population. The heavy metal operons and three biocide resistance genes were differentially distributed across 15 sequence types (STs) and 16 serotypes. The number of heavy metal operons and biocide resistance genes per genome was significantly associated with high number of antimicrobial resistance (AMR) genes per genome. Notable is the mercury operon which exhibited significant association with genes conferring resistance to aminoglycosides, cephalosporins, diaminopyrimidine, sulfonamide, and fosfomycin. The mercury operon was co-located with the AMR genes aac(3)-IV, ant(3”)-IIa, aph(3’)-Ia, and aph(4)-Ia, CTX-M-65, dfrA14, sul1, and fosA3 genes within the same plasmid types. Lastly, we found evidence for negative selection of individual genes of each heavy metal operon and the biocide resistance genes (dN/dS < 1). Our study highlights the need for continued surveillance of S. enterica serotypes that carry those genes that confer resistance to heavy metals and biocides that are often associated with mobile AMR genes. The selective pressures imposed by heavy metals and biocides on S. enterica may contribute to the co-selection and spread of AMR in human infections.

Urban Wildlife Crisis: Australian Silver Gull Is a Bystander Host to Widespread Clinical Antibiotic Resistance

The Australian silver gull is an urban-adapted species that frequents anthropogenic waste sites. The enterobacterial flora of synanthropic birds often carries antibiotic resistance genes. Whole-genome sequence analyses of 425 Escherichia coli isolates from cloacal swabs of chicks inhabiting three coastal sites in New South Wales, Australia, cultured on media supplemented with meropenem, cefotaxime, or ciprofloxacin are reported. Phylogenetically, over 170 antibiotic-resistant lineages from 96 sequence types (STs) representing all major phylogroups were identified. Remarkably, 25 STs hosted the carbapenemase gene bla_IMP-4, sourced only from Five Islands. Class 1 integrons carrying bla_IMP and bla_OXA alongside bla_CTX-M and qnrS were notable. Multiple plasmid types mobilized bla_IMP-4 and bla_OXA-1, and 121 isolates (28%) carried either a ColV-like (18%) or a pUTI89-like (10%) F virulence plasmid. Phylogenetic comparisons to human isolates provided evidence of interspecies transmission. Our study underscores the importance of bystander species in the transmission of antibiotic-resistant and pathogenic E. coli. IMPORTANCE By compiling various genomic and phenotypic data sets, we have provided one of the most comprehensive genomic studies of Escherichia coli isolates from the Australian silver gull, on media containing clinically relevant antibiotics. The analysis of genetic structures capturing antimicrobial resistance genes across three gull breeding colonies in New South Wales, Australia, and comparisons to clinical data have revealed a range of trackable genetic signatures that highlight the broad distribution of clinical antimicrobial resistance in more than 170 different lineages of E. coli. Conserved truncation sizes of the class 1 integrase gene, a key component of multiple-drug resistance structures in the Enterobacteriaceae, represent unique deletion events that are helping to link seemingly disparate isolates and highlight epidemiologically relevant data between wildlife and clinical sources. Notably, only the most anthropogenically affected of the three sites (Five Islands) was observed to host carbapenem resistance, indicating a potential reservoir among the sites sampled.

Formation, Transmission, and Dynamic Evolution of a Multidrug-Resistant Chromosomally Integrated Plasmid in Salmonella Spp

IncHI2 plasmids, possessing high flexibility and genetic plasticity, play a vital role in the acquisition and transmission of resistance determinants. Polymorphic mobile genetic elements (MGEs) generated by a chromosomally integrated IncHI2 plasmid in an individual Salmonella isolate have not yet been detected, and the mechanisms of the formation, excision, and dynamic evolution of a multidrug-resistant chromosomally integrated plasmid (MRCP) have remained obscure. Herein, we identified a 260-kb bla_CTX–M–55-qnrS1-bearing IncHI2 plasmid within a Salmonella Muenster strain. Plenty of heterogeneous MGEs (new Escherichia coli chromosomally integrated plasmid or circular plasmids with different profiles) were yielded when this MRCP was conjugated into E. coli J53 with a transfer frequency of 10^–4–10^–5 transconjugants per donor. A bioinformatic analysis indicated that replicative transposition and homologous recombination of IS26 elements were particularly active, and the truncated Tn1721 also played a vital role in the formation of MRCP offspring. More importantly, when released from the chromosome, MRCP could capture and co-transfer adjacent chromosomal segments to form larger plasmid progeny than itself. Stability and growth kinetics assays showed that the biological characteristics of MRCP progeny were differentiated. This study provides an insight into a flexible existence of MRCP. The conversion between vertical and horizontal transmission endowed MRCP with genetic stability as a chromosomal coding structure and transferability as extra-chromosomal elements. This alternation may accelerate the acquisition and persistence of antibiotic resistance of clinical pathogens and enhance their ability to respond to adverse environments, which poses a great challenge to the traditional antibiotic treatment.

Evolution of Copper Homeostasis and Virulence in Salmonella

Salmonella enterica sv. Typhimurium modulates the expression of factors essential for virulence, contributing to its survival against the surge of copper (Cu) in the Salmonella-containing vacuole. This bactericidal host innate immune component primarily targets the bacterial envelope, where most cuproproteins are localized. While in most enteric species periplasmic Cu homeostasis is maintained by the CusR/CusS-controlled CusCFBA efflux system encoded in the cus locus, we noticed that these genes were lost from the Salmonella-core genome. At the same time, Salmonella acquired cueP, coding for a periplasmic Cu chaperone. As cus, cueP was shown to be essential for bacterial survival in a copper-rich environment under anaerobiosis, suggesting that it can functionally substitute the CusCFBA system. In the present study, the whole Escherichia coli cus locus was reintroduced to the chromosome of the Salmonella wild-type or the ΔcueP strain. While the integrated cus locus did not affect Cu resistance under aerobic conditions, it increases Cu tolerance under anaerobiosis, irrespective of the presence or absence of cueP. In contrast to the Cus system, CueP expression is higher at high copper concentrations and persisted over time, suggesting separate functions. Finally, we observed that, regardless of the presence or absence of cus, a mutant deleted of cueP shows a deficiency in replication inside macrophages compared to the wild-type strain. Our results demonstrate that CueP and CusCFBA exert redundant functions for metal resistance, but not for intracellular survival, and therefore for the virulence of this pathogen.

In Silico Detection of Antimicrobial Resistance Integrons in Salmonella enterica Isolates from Countries of the Andean Community

Antimicrobial resistance genes are often associated with integrons, which promote their movement between and within DNA molecules. IntFinder 1.0 and I-VIP v1.2 were used for the detection of integrons and their associated resistance genes in assembled sequences and raw reads. A dataset comprising 1688 sequenced Salmonella enterica isolates from countries of the Andean Community was developed. A total of 749 and 680 integrons were identified by IntFinder 1.0 and I-VIP v1.2, respectively; class 2 integrons were the most abundant followed by class 1, whereas no class 3 integrons were detected. These elements were mainly associated with isolates from animal sources. S. Infantis ST32 contained the majority of integrons. Trimethoprim resistance genes (dfrA) were found in greater numbers than others, including aadA and bla genes. The presence of these resistance integrons may come as a response to antibiotic misuse, especially of co-trimoxazole. This represents a public health risk as novel resistant strains might appear due to gene dissemination. The information gathered from in silico studies not only contributes to our understanding of integron dynamics in pathogenic Salmonella, but also helps identify potential emergent patterns of resistance in the region, which is fundamental for developing pertinent antibiotic surveillance programs.

Laboratory Stock Variants of the Archetype Silver Resistance Plasmid pMG101 Demonstrate Plasmid Fusion, Loss of Transmissibility, and Transposition of Tn7/pco/sil Into the Host Chromosome

Salmonella Typhimurium carrying the multidrug resistance (MDR) plasmid pMG101 was isolated from three burns patients in Boston United States in 1973. pMG101 was transferrable into other Salmonella spp. and Escherichia coli hosts and carried what was a novel and unusual combination of AMR genes and silver resistance. Previously published short-read DNA sequence of pMG101 showed that it was a 183.5Kb IncHI plasmid, where a Tn7-mediated transposition of pco/sil resistance genes into the chromosome of the E. coli K-12 J53 host strain had occurred. We noticed differences in streptomycin resistance and plasmid size between two stocks of E. coli K-12 J53 pMG101 we possessed, which had been obtained from two different laboratories (pMG101-A and pMG101-B). Long-read sequencing (PacBio) of the two strains unexpectedly revealed plasmid and chromosomal rearrangements in both. pMG101-A is a non-transmissible 383Kb closed-circular plasmid consisting of an IncHI2 plasmid sequence fused to an IncFI/FIIA plasmid. pMG101-B is a mobile closed-circular 154 Kb IncFI/FIIA plasmid. Sequence identity of pMG101-B with the fused IncFI/IncFIIA region of pMG101-A was >99%. Assembled host sequence reads of pMG101-B showed Tn7-mediated transposition of pco/sil into the E. coli J53 chromosome between yhiM and yhiN. Long read sequence data in combination with laboratory experiments have demonstrated large scale changes in pMG101. Loss of conjugation function and movement of resistance genes into the chromosome suggest that even under long-term laboratory storage, mobile genetic elements such as transposons and insertion sequences can drive the evolution of plasmids and host. This study emphasises the importance of utilising long read sequencing technologies of plasmids and host strains at the earliest opportunity.

Antibiotic Susceptibility Profile and Tetracycline Resistance Genes Detection in Salmonella spp. Strains Isolated from Animals and Food

Salmonella spp. is among the leading causes of foodborne infections in humans and a large number of animals. Salmonella spp. is a pathogen involved in the dissemination of antimicrobial resistance because it can accumulate antibiotic resistance genes (ARGs). In this study, the antibiotic resistance profile to 15 antibiotics, belonging to six different classes, of 60 strains of Salmonella spp. collected from pets, farm animals, wildlife, and food in Sicily (Italy) was investigated by the Kirby-Bauer method. Given that almost 33.3% of the Salmonella spp. strains were resistant to tetracycline, Real-Time PCR analysis was applied on all the 60 strains to detect the presence of eight selected tet resistance genes. Besides, the presence of the int1 gene, related to the horizontal gene transfer among bacteria, was also investigated in all the strains by Real-Time PCR analysis. Our data showed that 56% of the isolated strains harbored one or more tet resistance genes and that these strains were most frequently isolated from animals living in close contact with humans. Concerning int1, 17 strains (28.3%) harbored this genetic element and eight of these simultaneously contained tet genes. The results of this study highlight the importance of using a molecular approach to detect resistance genetic determinants, whose spread can increase the diffusion of multidrug-resistant strains. Besides, the study of zoonotic bacteria such as Salmonella spp. which significantly contribute to ARGs dissemination should always follow a One Health approach that considers the health of humans, animals, and the environment to be closely related.

Bacterial zoonoses transmitted by household pets and as reservoirs of antimicrobial resistant bacteria

Numerous individuals are committed to growing pet creatures like cats, dogs, and rats etc., pay care for them and as a result of this, there's a boost of their populace in advanced culture. The close interaction between family pets and individuals offers ideal conditions for bacterial transmission. Distinctive sorts of antimicrobial agents are exploited for animal husbandry and studies have revealed that many bacteria have attained confrontation against them viz., Staphylococcus intermedius, Escherichia coli, methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococci and multidrug-resistant Salmonella typhi etc. and a few of these are a prospective for zoonotic transmission. In the current review, the attention has been paid on how household pets, especially dogs disperse the antimicrobial resistance in contrast to that of food animals. A lot of evidences are accessible on food animals and nation-wide scrutiny programmes solely hub on food animals; therefore, for steerage antimicrobial use policy in small animal veterinary exercise as well as for gauging the chance of transmission of antimicrobial resistance to humans' statistics on pet animals are sincerely needed. Transmission of such organisms, especially pathogenic staphylococci, occurs between pets, owners, and veterinary staff, and pets can act as reservoirs of such bacteria; this may additionally have an impact on the use of antimicrobials in human medicine. There is a need to generate statistics concerning each the levels of carriage of such microorganism in pets and the risk factors associated with the switch of the microorganism to human beings who have contact with infected pets, as nicely as to improve hygiene measures in veterinary practice.

Prevalence, genomic characteristics, and transmission dynamics of mcr-1-positive Salmonella enterica Typhimurium from patients with infectious diarrhea

BACKGROUND

Previous studies reported the prevalence of mcr-1 among clinical infected Salmonella isolates in China. However, the transmission dynamics of mcr-1 in different ecological niches were not well investigated. Our objective is to exhibit the transmission dynamics of mcr-1 in Salmonella.

METHODS

598 Salmonella isolates were recovered from ten hospitals; besides 936 pig faces and 167 pork samples were collected from January 2015 to December 2017 in Guangzhou, China. PCR and sequencing were used to identify mcr-1-positive Salmonella. Antimicrobial susceptibility testing was performed with 16 antimicrobials. Conjugation, S1-PFGE, and Southern blot were used to determine the transferability and location of mcr-1. Whole-genome sequencing was used to investigate pangenome, phylogeny, plasmid, and transposon.

RESULTS

Eleven mcr-1-positive Salmonella isolates were identified from patients with infectious diarrhea. Five pig fecal samples and three pork samples contained mcr-1-positive Salmonella isolates. All isolates were multi-drug resistant. The mcr-1 genes were located on ∼210-250 kb IncHI2-pST3 plasmids, and 12 mcr-1 genes were transferable. All isolates were assigned to ST34 or its genetically closed STs. The distribution of the core-genome network was significantly correlated with source distributions. The accessory genes-based network demonstrated that the diverse clonal complexes could share highly similar accessory genomes.

CONCLUSIONS

The prevalence of mcr-1-positive Salmonella among different sources was low. Clonal transmission could not be the main reason for the expansion of mcr-1-positive Salmonella, but be attributed to the horizontal transfer of IncHI2-pST3 plasmid. Continuous surveillance on Salmonella should be performed to investigate the response of colistin banning in food-producing animals by mcr-1-positive Salmonella populations.

Emergence of High Level Carbapenem and Extensively Drug Resistant Escherichia coli ST746 Producing NDM-5 in Influent of Wastewater Treatment Plant, Seoul, South Korea

High level carbapenem and extensively drug resistant (XDR) Escherichia coli strain N7, which produces a variant of New Delhi metallo-β-lactamase (NDM-5), was isolated from the influent of the Jungnang wastewater treatment plant located on Han River, Seoul, South Korea. Phenotypic and genotypic resistances to carbapenem were tested using agar and broth dilution methods, and polymerase chain reaction. Whole-genome sequencing was performed to characterize the genetic structure of strain N7. E. coli strain N7, which harbors the bla NDM-5 gene, showed high level of carbapenem resistance at concentrations of doripenem (512 mg/L) and meropenem (256 mg/L), and XDR to 15 antibiotics. Based on the genomic sequence analysis, two plasmids, a hybrid IncHI2/N-type and an IncX3 type, were present. The former contains a cluster (bla NDM-5-ble MBL -trpF-dsbD) bracketed by multi-insertional sequences, IS3000, ISAba125, IS5, and IS26. The latter carries the following resistance genes: bla CTX-14, aac(3)-IV, aadA1, aadA2, aph(3')-Ia, aph(4)-Ia, sul1, sul2, sul3, dfrA12, fosA3, oqxA, oqxB, mph(A), and floR, and cmlA1. The chromosome, contig3, and contig5 also carry bla CTX-64 and mdf(A), tet(A), and erm(B), tet(M) and aadA22, respectively. Strain N7 also harbors virulence factors such as fimH, flu, ecpABCDE, sfmA, hlyE, and gadA. This study demonstrates the emergence of high level carbapenem resistant XDR E. coli strain N7 containing bla NDM-5 in aquatic environment, Seoul, South Korea. Due to the presence of mobile genetic elements, this strain could horizontally transfer resistance genes, including bla NDM-5 to environmental bacteria. Thus, it is necessary to conduct continuous surveillance for carbapenem resistance in various aquatic environments.

Characterization of a novel class 1 integron InSW39 and a novel transposon Tn5393k identified in an imipenem-nonsusceptible Salmonella Typhimurium strain in Sichuan, China

This study aimed to characterize molecular mechanism of 3 Salmonella enterica strains and novel mobile genetic elements identified in them. The strains, designated SW1, SW39, and SW109084, were obtained from diarrhea patients. The results of susceptibility testing showed SW39 was nonsusceptible to imipenem and cefotaxime. Whole genome sequencing was performed on Illumina HiSeq platform. Multilocus-sequence typing revealed SW1 belonged to ST2529 which was first confirmed in S. enterica, SW109084 was ST34 which was first reported in Enteritidis and SW39 was ST19. Resistome analysis showed SW1, SW109084, and SW39 carried 14, 19, and 17 antibiotic resistance genes. Seven transposons and 4 integrons were confirmed in these strains. Notably, a novel In6- and In7-like class 1 integron designated InSW39 and a novel transposon Tn5393k were identified in plasmid pSW39. The study of genomics and resistance in S. enterica plays a significant role in prevention and treatment of Salmonella infections.

Persistence of extended-spectrum β-lactamase plasmids among Enterobacteriaceae in commercial broiler farms

To clarify the persistence of extended-spectrum β-lactamase (ESBL) producers, 13 plasmids from two broiler farms were analyzed. On the farm not using antimicrobials, one plasmid from Klebsiella pneumoniae isolated from a day-old chick was similar to that from Escherichia coli isolated a year later, with the deletion of two transposons. On the farm using antimicrobials, most circulating plasmids (eight out of nine) in a flock of 40-days-old chicks were identical, although one from K. pneumoniae had a deletion of a transposon carrying a class 1 integron containing aadA2 and dfrA12. Thus, ESBL plasmids persisted in the farms with or without antimicrobial agent use.

Genomic Characterisation of a Multiple Drug Resistant IncHI2 ST4 Plasmid in Escherichia coli ST744 in Australia

Antibiotic resistance genes (ARGs) including those from the bla_CTX-M family and mcr-1 that encode resistance to extended spectrum β–lactams and colistin, respectively, have been linked with IncHI2 plasmids isolated from swine production facilities globally but not in IncHI2 plasmids from Australia. Here we describe the first complete sequence of a multiple drug resistance Australian IncHI2-ST4 plasmid, pTZ41_1P, from a commensal E. coli from a healthy piglet. pTZ41_1P carries genes conferring resistance to heavy-metals (copper, silver, tellurium and arsenic), β-lactams, aminoglycosides and sulphonamides. The ARGs reside within a complex resistance locus (CRL) that shows considerable sequence identity to a CRL in pSDE_SvHI2, an IncHI2:ST3 plasmid from an enterotoxigenic E. coli with serotype O157:H19 of porcine origin that caused substantial losses to swine production operations in Australia in 2007. pTZ41_1P is closely related to IncHI2 plasmids found in E. coli and Salmonella enterica from porcine, avian and human sources in Europe and China but it does not carry genes encoding resistance to clinically-important antibiotics. We identified regions of IncHI2 plasmids that contribute to the genetic plasticity of this group of plasmids and highlight how they may readily acquire new resistance gene cargo. Genomic surveillance should be improved to monitor IncHI2 plasmids.

Escherichia coli ST302: Genomic Analysis of Virulence Potential and Antimicrobial Resistance Mediated by Mobile Genetic Elements

aEPEC are associated with persistent diarrhea, and diarrheal outbreaks in both humans and animals worldwide. They are differentiated from typical EPEC by the lack of bundle-forming pili, and from EHEC by the lack of phage-mediated stx toxins. However, phylogenetic analyses often associate aEPEC with EHEC, promoting the hypothesis that aEPEC are the progenitors of EHEC, which is supported by aEPEC conversion to EHEC by stx-carrying phages. While aEPEC can cause disease outright, the potential to acquire stx, one of the most potent bacterial toxins known, merits close monitoring. Escherichia coli ST302 (O108:H9, O182:H9, O45:H9) are aEPEC that have been isolated from diarrheic human, pig and rabbit hosts, as well as in healthy pigs, however, no study to date has focused on E. coli ST302 strains. Through WGS and hybrid assembly we present the first closed chromosome, and two circularized plasmids of an ST302 strain - F2_18C, isolated from a healthy pig in Australia. A phylogenetic analysis placed E. coli ST302 strains in proximity to EHEC ST32 (O145:H28) strains. Public databases were interrogated for WGSs of E. coli ST302 strains and short-read gene screens were used to compare their virulence-associated gene (VAG) and antimicrobial resistance gene (ARG) cargo. E. coli ST302 strains carry diverse VAGs, including those that typically associated with extraintestinal pathogenic E. coli (ExPEC). Plasmid comparisons showed that pF2_18C_FIB shared homology with EHEC virulence plasmids such as pO103 while pF2_18C_HI2 is a large multidrug resistance IncHI2:ST3 plasmid. A comparison of 33 HI2:ST3 plasmids demonstrated that those of Australian origin have not acquired resistances to extended-spectrum beta-lactams, colistin, fosfomycin or rifampicin, unlike those originating from Asia. F2_18C was shown to carry two additional pathogenicity islands – ETT2, and the STEC-associated PAI_CL3, plasmid-associated heavy metal resistance genes, as well as several unoccupied stx-phage attachment sites. This study sheds light on the virulence and AMR potential of E. coli ST302 strains and informs AMR genomic surveillance.

Z/I1 Hybrid Virulence Plasmids Carrying Antimicrobial Resistance genes in S. Typhimurium from Australian Food Animal Production

Knowledge of mobile genetic elements that capture and disseminate antimicrobial resistance genes between diverse environments, particularly across human-animal boundaries, is key to understanding the role anthropogenic activities have in the evolution of antimicrobial resistance. Plasmids that circulate within the Enterobacteriaceae and the Proteobacteria more broadly are well placed to acquire resistance genes sourced from separate niche environments and provide a platform for smaller mobile elements such as IS26 to assemble these genes into large, complex genomic structures. Here, we characterised two atypical Z/I1 hybrid plasmids, pSTM32-108 and pSTM37-118, hosting antimicrobial resistance and virulence associated genes within endemic pathogen Salmonella enterica serovar Typhimurium 1,4,[5],12:i:-, sourced from Australian swine production facilities during 2013. We showed that the plasmids found in S. Typhimurium 1,4,[5],12:i:- are close relatives of two plasmids identified from Escherichia coli of human and bovine origin in Australia circa 1998. The older plasmids, pO26-CRL₁₂₅ and pO111-CRL₁₁₅, encoded a putative serine protease autotransporter and were host to a complex resistance region composed of a hybrid Tn21-Tn1721 mercury resistance transposon and composite IS26 transposon Tn6026. This gave a broad antimicrobial resistance profile keyed towards first generation antimicrobials used in Australian agriculture but also included a class 1 integron hosting the trimethoprim resistance gene dfrA5. Genes encoding resistance to ampicillin, trimethoprim, sulphonamides, streptomycin, aminoglycosides, tetracyclines and mercury were a feature of these plasmids. Phylogenetic analyses showed very little genetic drift in the sequences of these plasmids over the past 15 years; however, some alterations within the complex resistance regions present on each plasmid have led to the loss of various resistance genes, presumably as a result of the activity of IS26. These alterations may reflect the specific selective pressures placed on the host strains over time. Our studies suggest that these plasmids and variants of them are endemic in Australian food production systems.

Diverse Mobile Genetic Elements and Conjugal Transferability of Sulfonamide Resistance Genes (sul1, sul2, and sul3) in Escherichia coli Isolates From Penaeus vannamei and Pork From Large Markets in Zhejiang, China

High prevalence rates of sulfonamide resistance genes sul1, sul2, and sul3 have been observed in Gram-negative bacteria isolated from humans, domestic animals, and aquaculture species worldwide. We investigated the distribution characteristics, location, conjugative transferability, and genetic environments of sul genes from Escherichia coli isolates collected from Penaeus vannamei and pork samples from three large markets in Zhejiang, China. The prevalence rates of sul genes in sulfonamide-resistant E. coli isolates from P. vannamei and pork samples were 90.0 and 88.6%, respectively, and the prevalence of sul1 and sul2 was significantly higher than that of sul3 (p < 0.05). Twenty-four representative sul-positive E. coli isolates were analyzed in detail. Southern blot hybridization confirmed that sul genes of E. coli isolates were located on plasmids and/or chromosomes. Transfer of resistance through conjugation was observed in all 18 E. coli isolates harboring sul genes on plasmids. Replicon typing identified seven different incompatibility groups and IncF was the dominant replicon type among sul gene-containing plasmids from both sources. PCR walking analysis indicated that 87.5% (35/40) of sul gene-related fragments carried insertion sequences (ISs) belonging to a variety of families in diverse sites, with IS26 occurring most frequently. In addition, the sul1 gene was detected mainly in fragments carrying class 1 integrons. Co-location on the same fragment with resistance genes that may contribute to the persistence and dissemination of sul1 and/or sul2 genes. The diversity of mobile genetic elements and resistance genes adjacent to sul3 was much lower than those adjacent to sul1 and sul2, especially those located in chromosomes, which reduced the transmission potential of the sul3 gene. In conclusion, combined with the results of clonal relatedness analysis by PFGE and MLST of 24 representative E. coli isolates from P. vannamei and pork samples, it showed that a small number of sul genes were vertically transmitted among E. coli from P. vannamei and that horizontal gene transfer was likely the main transmission mechanism of sul genes from both sources. Our results provide important information to better understand the risk of transmission of sul genes from seafood and meat to humans.