Klebsiella pneumoniae Complex Harboring mcr-1, mcr-7, and mcr-8 Isolates from Slaughtered Pigs in Thailand

Epidemiological, Virulence, and Antibiotic Resistance Analysis of Klebsiella pneumoniae, a Major Source of Threat to Livestock and Poultry in Some Regions of Xinjiang, China

Klebsiella pneumoniae (K. pneumoniae) is recognized as a zoonotic pathogen with an increasing threat to livestock and poultry. However, research on K. pneumoniae of animal origin remains limited. To address the gap, a comprehensive investigation was carried out by collecting a total of 311 samples from the farms of four animal species (dairy cow, chicken, sheep, and pig) in selected areas of Xinjiang, China. Isolates were identified by khe gene amplification and 16S rRNA gene sequencing. Genotyping of K. pneumonia isolates was performed using wzi typing and multilocus sequence typing (MLST). PCR was employed to identify virulence and resistance genes. An antibiotic susceptibility test was conducted using the Kirby-Bauer method. The findings revealed an isolation of 62 K. pneumoniae strains, with an average isolation rate of 19.94%, with the highest proportion originating from cattle sources (33.33%). Over 85.00% of these isolates harbored six virulence genes (wabG, uge, fimH, markD, entB, and ureA); while more than 75.00% of isolates possessed four resistance genes (blaTEM, blaSHV, oqxA, and gyrA). All isolates exhibited complete resistance to ampicillin and demonstrated substantial resistance to sulfisoxazole, amoxicillin/clavulanic acid, and enrofloxacin, with an antibiotic resistance rate of more than 50%. Furthermore, 48.39% (30/62) of isolates were classified as multidrug-resistant (MDR) strains, with a significantly higher isolation rate observed in the swine farms (66.67%) compared to other farms. Genetic characterization revealed the classification of the 62 isolates into 30 distinct wzi allele types or 35 different sequence types (STs). Notably, we identified K. pneumoniae strains of dairy and swine origin belonging to the same ST42 and wzi33-KL64 types, as well as strains of dairy and chicken origin belonging to the same wzi31-KL31-K31 type. These findings emphasize the widespread occurrence of drug-resistant K. pneumoniae across diverse animal sources in Xinjiang, underscoring the high prevalence of multidrug resistance. Additionally, our results suggest the potential for animal-to-animal transmission of K. pneumoniae and there was a correlation between virulence genes and antibiotic resistance genes. Moreover, the current study provides valuable data on the prevalence, antibiotic resistance, and genetic diversity of K. pneumoniae originating from diverse animal sources in Xinjiang, China.

Genetic characterization of multidrug-resistant Escherichia coli harboring colistin-resistant gene isolated from food animals in food supply chain

Colistin is widely used for the prophylaxis and treatment of infectious disease in humans and livestock. However, the global food chain may actively promote the dissemination of colistin-resistant bacteria in the world. Mobile colistin-resistant (mcr) genes have spread globally, in both communities and hospitals. This study sought to genomically characterize mcr-mediated colistin resistance in 16 Escherichia coli strains isolated from retail meat samples using whole genome sequencing with short-read and long-read platforms. To assess colistin resistance and the transferability of mcr genes, antimicrobial susceptibility testing and conjugation experiments were conducted. Among the 16 isolates, 11 contained mcr-1, whereas three carried mcr-3 and two contained mcr-1 and mcr-3. All isolates had minimum inhibitory concentration (MIC) for colistin in the range 1-64 μg/mL. Notably, 15 out of the 16 isolates demonstrated successful transfer of mcr genes via conjugation, indicative of their presence on plasmids. In contrast, the KK3 strain did not exhibit such transferability. Replicon types of mcr-1-containing plasmids included IncI2 and IncX4, while IncFIB, IncFII, and IncP1 contained mcr-3. Another single strain carried mcr-1.1 on IncX4 and mcr-3.5 on IncP1. Notably, one isolate contained mcr-1.1 located on a chromosome and carrying mcr-3.1 on the IncFIB plasmid. The chromosomal location of the mcr gene may ensure a steady spread of resistance in the absence of selective pressure. Retail meat products may act as critical reservoirs of plasmid-mediated colistin resistance that has been transmitted to humans.

Convergence of plasmid-mediated Colistin and Tigecycline resistance in Klebsiella pneumoniae

Objective

The co-occurrence of colistin and tigecycline resistance genes in Klebsiella pneumoniae poses a serious public health problem. This study aimed to characterize a K. pneumoniae strain, K82, co-harboring a colistin resistance gene (CoRG) and tigecycline resistance gene (TRG), and, importantly, investigate the genetic characteristics of the plasmid with CoRG or TRG in GenBank.

Methods

K. pneumoniae strain K82 was subjected to antimicrobial susceptibility testing, conjugation assay, and whole-genome sequencing (WGS). In addition, comparative genomic analysis of CoRG or TRG-harboring plasmids from K82 and GenBank was conducted. K. pneumoniae strain K82 was resistant to all the tested antimicrobials including colistin and tigecycline, except for carbapenems.

Results

WGS and bioinformatic analysis showed that K82 belonged to the ST656 sequence type and carried multiple drug resistance genes, including mcr-1 and tmexCD1-toprJ1, which located on IncFIA/IncHI2/IncHI2A/IncN/IncR-type plasmid pK82-mcr-1 and IncFIB/IncFII-type plasmid pK82-tmexCD-toprJ, respectively. The pK82-mcr-1 plasmid was capable of conjugation. Analysis of the CoRG/TRG-harboring plasmid showed that mcr-8 and tmexCD1-toprJ1 were the most common CoRG and TRG of Klebsiella spp., respectively. These TRG/CoRG-harboring plasmids could be divided into two categories based on mash distance. Moreover, we found an IncFIB/IncHI1B-type plasmid, pSYCC1_tmex_287k, co-harboring mcr-1 and tmexCD1-toprJ1. To the best of our knowledge, this is the first report on the co-occurrence of mcr-1 and tmexCD1-toprJ1 on a single plasmid.

Conclusion

Our research expands the known diversity of CoRG and TRG-harboring plasmids in K. pneumoniae. Effective surveillance should be implemented to assess the prevalence of co-harboring CoRG and TRG in a single K. pneumoniae isolate or even a single plasmid.

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

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

Farm to table: colistin resistance hitchhiking through food

Colistin is a high priority, last-resort antibiotic recklessly used in livestock and poultry farms. It is used as an antibiotic for treating multi-drug resistant Gram-negative bacterial infections as well as a growth promoter in poultry and animal farms. The sub-therapeutic doses of colistin exert a selection pressure on bacteria leading to the emergence of colistin resistance in the environment. Colistin resistance gene, mcr are mostly plasmid-mediated, amplifying the horizontal gene transfer. Food products such as chicken, meat, pork etc. disseminate colistin resistance to humans through zoonotic transfer. The antimicrobial residues used in livestock and poultry often leaches to soil and water through faeces. This review highlights the recent status of colistin use in food-producing animals, its association with colistin resistance adversely affecting public health. The underlying mechanism of colistin resistance has been explored. The prohibition of over-the-counter colistin sales and as growth promoters for animals and broilers has exhibited effective stewardship of colistin resistance in several countries.

Special Issue: “New Methods in Microbial Research 2.0”: Editorial

Today, it is definitively accepted that microorganisms play a central role in the functioning and maintenance of our planet and the organisms thriving on it [...]

Identification and characterization of plasmids carrying the mobile colistin resistance gene mcr-1 using optical DNA mapping

Objectives

Colistin is a last-resort antibiotic, but there has been a rapid increase in colistin resistance, threatening its use in the treatment of infections with carbapenem-resistant Enterobacterales (CRE). Plasmid-mediated colistin resistance, in particular the mcr-1 gene, has been identified and WGS is the go-to method in identifying plasmids carrying mcr-1 genes. The goal of this study is to demonstrate the use of optical DNA mapping (ODM), a fast, efficient and amplification-free technique, to characterize plasmids carrying mcr-1.

Methods

ODM is a single-molecule technique, which we have demonstrated can be used for identifying plasmids harbouring antibiotic resistance genes. We here applied the technique to plasmids isolated from 12 clinical Enterobacterales isolates from patients at a major hospital in Thailand and verified our results using Nanopore long-read sequencing.

Results

We successfully identified plasmids encoding the mcr-1 gene and, for the first time, demonstrated the ability of ODM to identify resistance gene sites in small (∼30 kb) plasmids. We further identified bla _CTX-M genes in different plasmids than the ones encoding mcr-1 in three of the isolates studied. Finally, we propose a cut-and-stretch assay, based on similar principles, but performed using surface-functionalized cover slips for DNA immobilization and an inexpensive microscope with basic functionalities, to identify the mcr-1 gene in a plasmid sample.

Conclusions

Both ODM and the cut-and-stretch assay developed could be very useful in identifying plasmids encoding antibiotic resistance in hospitals and healthcare facilities. The cut-and-stretch assay is particularly useful in low- and middle-income countries, where existing techniques are limited.

Multiplex PCR Detection of Common Carbapenemase Genes and Identification of Clinically Relevant Escherichia coli and Klebsiella pneumoniae Complex

Carbapenem-resistant Enterobacterales (CRE) species are top priority pathogens according to the World Health Organization. Rapid detection is necessary and useful for their surveillance and control globally. This study developed a multiplex polymerase chain reaction (mPCR) detection of the common carbapenemase genes NDM, KPC, and OXA-48-like, together with identification of Escherichia coli, and distinguished a Klebsiella pneumoniae complex to be K. pneumoniae, K. quasipneumoniae, and K. variicola. Of 840 target Enterobacterales species, 190 E. coli, 598 K. pneumoniae, 28 K. quasipneumoniae, and 23 K. variicola. with and without NDM, KPC, or OXA-48-like were correctly detected for their species and carbapenemase genes. In contrast, for the Enterobacterales species other than E. coli or K. pneumoniae complex with carbapenemase genes, the mPCR assay could detect only NDM, KPC, or OXA-48-like. This PCR method should be useful in clinical microbiology laboratories requiring rapid detection of CRE for epidemiological investigation and for tracking the trends of carbapenemase gene dynamics.

One Health Analysis of mcr-Carrying Plasmids and Emergence of mcr-10.1 in Three Species of Klebsiella Recovered from Humans in China

The global dissemination of the mobile colistin resistance (mcr) gene illustrates how the use of colistin in veterinary medicine can affect human health, exemplifying the concept of One Health. This study screened for the existence of mcr variants (from mcr-1 to mcr-10) in a 5-year collection of clinical Klebsiella short-read whole-genome sequencing (WGS) data from a tertiary hospital in China (2013 to 2018) and aimed to identify the mechanisms of mcr spread. MICs were measured for the mcr-positive isolates, and long-read sequencing was performed to complete the mcr-positive genome sequences. Six variants (mcr-1.1, mcr-8.1, mcr-8.2, mcr-9.1, mcr-9.2, and mcr-10.1) were identified in 20 genomes, with plasmids from the IncFII_K, IncHI2, IncI2, and IncX4 groups. Highly similar plasmids (coverage, >75%; nucleotide identity, >98.5%) isolated from silver gulls, chickens, pigs, wastewater treatment plants, and hospital sewage were identified in GenBank. The MICs of the mcr-1- and mcr-8-carrying isolates were ≥4 μg/mL; however, the MICs of the mcr-9- and mcr-10-carrying isolates ranged from 0.5 μg/mL to 1 μg/mL (colistin susceptible). The variants mcr-1 to mcr-9 were found only in Klebsiella pneumoniae, while mcr-10.1 was found in K. pneumoniae, Klebsiella quasipneumoniae subsp. quasipneumoniae, and Klebsiella variicola. A pair of inverted repeats (IRs) was identified for hsdSMR-ISEc36-mcr-10.1-xerC; IR-1 (5'-TCAAACGTA) was inside the attL site of xerC, indicating that mcr-10.1 was originally integrated by xerC and mobilized by ISEc36 afterwards. In conclusion, this is the first report of mcr-10.1 susceptible to colistin in three species of Klebsiella. This study shows the genetic events that happened to mcr-10.1 in a stepwise manner, with the first step being XerC integration and the second being ISEc36 mobilization. Finally, this study also highlights mcr transmission between humans and nature. IMPORTANCE Reports of mcr-1 and mcr-8 are common in China; however, few studies have reported mcr-9 and mcr-10. One reason is that the newly described variants can be phenotypically colistin susceptible and thus may not be identified. This study identified the mcr-positive clinical isolates by investigating WGS data for 2,855 Klebsiella isolates (including K. pneumoniae, K. quasipneumoniae subsp. quasipneumoniae, and K. variicola) and found three mcr-9 and three mcr-10 cases (MICs, 0.5 μg/mL to 1 μg/mL; colistin susceptible). This study also reveals a pair of perfect 9-bp IRs of ISEc36 and the precise mcr-10.1 integration and insertion events that happened to the IncFII_K plasmids. A One Health analysis of highly similar plasmid structures from human and nonhuman sources emphasizes the plasmid transmission and evolution process.

Plasmidome in mcr-1 harboring carbapenem-resistant enterobacterales isolates from human in Thailand

The emergence of the mobile colistin-resistance genes mcr-1 has attracted significant attention worldwide. This study aimed to investigate the genetic features of mcr-1-carrying plasmid among carbapenem-resistant Enterobacterales (CRE) isolates and the potential genetic basis governing transmission. Seventeen mcr-harboring isolates were analyzed based on whole genome sequencing using short-read and long-read platforms. All the mcr-1-carrying isolates could be conjugatively transferred into a recipient Escherichia coli UB1637. Among these 17 isolates, mcr-1 was located on diverse plasmid Inc types, consisting of IncX4 (11/17; 64.7%), IncI2 (4/17; 23.53%), and IncHI/IncN (2/17; 11.76%). Each of these exhibited remarkable similarity in the backbone set that is responsible for plasmid replication, maintenance, and transfer, with differences being in the upstream and downstream regions containing mcr-1. The IncHI/IncN type also carried other resistance genes (bla_TEM-1B or bla_TEM-135). The mcr-1-harboring IncX4 plasmids were carried in E. coli ST410 (7/11; 63.6%) and ST10 (1/11; 9.1%) and Klebsiella pneumoniae ST15 (1/11; 9.1%), ST336 (1/11; 9.1%), and ST340 (1/11; 9.1%). The IncI2-type plasmid was harbored in E. coli ST3052 (1/4; 25%) and ST1287 (1/4; 25%) and in K. pneumoniae ST336 (2/4; 50%), whereas IncHI/IncN were carried in E. coli ST6721 (1/2; 50%) and new ST (1/2; 50%). The diverse promiscuous plasmids may facilitate the spread of mcr-1 among commensal E. coli or K. pneumoniae strains in patients. These results can provide information for a surveillance system and infection control for dynamic tracing.

First report of Klebsiella pneumoniae co-producing OXA-181, CTX-M-55, and MCR-8 isolated from the patient with bacteremia

The worldwide spread of carbapenem-resistant Enterobacteriaceae (CRE) has led to a major challenge to human health. In this case, colistin is often used to treat the infection caused by CRE. However, the coexistence of genes conferring resistance to carbapenem and colistin is of great concern. In this work, we reported the coexistence of blaOXA-181, blaCTX-M-55, and mcr-8 in an ST273 Klebsiella pneumoniae isolate for the first time. The species identification was performed using MALDI-TOF MS, and the presence of various antimicrobial resistance genes (ARGs) and virulence genes were detected by PCR and whole-genome sequencing. Antimicrobial susceptibility testing showed that K. pneumoniae 5589 was resistant to aztreonam, imipenem, meropenem, ceftriaxone, cefotaxime, ceftazidime, levofloxacin, ciprofloxacin, gentamicin, piperacillin-tazobactam, cefepime, and polymyxin B, but sensitive to amikacin. S1-pulsed-field gel electrophoresis (PFGE) and Southern blotting revealed the mcr-8 gene was carried on a ~ 138 kb plasmid with a conserved structure (IS903B-ymoA-inhA-mcr-8-copR-baeS-dgkA-ampC). In addition, blaOXA-181 was found on another ~51 kb plasmid with a composite transposon flanked by insertion sequence IS26. The in vitro conjugation experiments and plasmid sequence probe indicated that the plasmid p5589-OXA-181 and the p5589-mcr-8 were conjugative, which may contribute to the propagation of ARGs. Relevant detection and investigation measures should be taken to control the prevalence of pathogens coharboring blaOXA-181, blaCTX-M-55 and mcr-8.

Distribution of mcr-1 Harboring Hypervirulent Klebsiella pneumoniae in Clinical Specimens and Lytic Activity of Bacteriophage KpnM Against Isolates

Background

The World Health Organization (WHO) has declared the multi-drug resistant (MDR) Klebsiella pneumoniae as one of the critical bacterial pathogens. The dearth of new antibiotics and inadequate therapeutic options necessitate finding alternative options. Bacteriophages are known as enemies of bacteria and are well-recognized to fight MDR pathogens.

Methods

A total of 150 samples were collected from different clinical specimens through a convenient sampling technique. Isolation, identification, and antibiotic susceptibility testing (AST) of K. pneumoniae were done by standard and validated microbiological procedures. Molecular identification of virulence factors and antibiotic resistance genes (ARGs) was carried out through polymerase chain reaction (PCR) by using specific primers. For bacteriophage isolation, hospital sewage samples were processed for phage enrichment, purification, and further characterization ie, transmission electron microscopy (TEM) and stability testing, etc. followed by evaluation of the lytic potential of the phage.

Results

Overall, a total of 41% of isolates of K. pneumoniae were observed as hypervirulent K. pneumoniae (hvKp). Among hvKp, a total of 12 (42%) were detected as MDR hvKp. A total of 37% of all MDR isolates were found resistant to colistin, and 66% of the colistin resistance isolates were recorded as mcr-1 positive. Isolated phage KpnM had shown lytic activity against 53 (79%) K. pneumoniae isolates. Remarkably, all 8 mcr-1 harboring MDR hvKp and non-hvKp isolates were susceptible to KpnM phage.

Conclusion

Significant distribution of mcr-1 harboring hypervirulent Klebsiella pneumoniae was observed in clinical specimens, which is worrisome for the health system of the country. Characterized phage KpnM exhibited encouraging results and showed the lytic activity against the mcr-1 harboring hvKp isolates, which may be used as a prospective alternative control strategy to fight this ominous bacterium.

MgrB Mutations and Altered Cell Permeability in Colistin Resistance in Klebsiella pneumoniae

There has been a resurgence in the clinical use of polymyxin antibiotics such as colistin due to the limited treatment options for infections caused by carbapenem-resistant Enterobacterales (CRE). However, this last-resort antibiotic is currently confronted with challenges which include the emergence of chromosomal and plasmid-borne colistin resistance. Colistin resistance in Klebsiella pneumoniae is commonly caused by the mutations in the chromosomal gene mgrB. MgrB spans the inner membrane and negatively regulates PhoP phosphorylation, which is essential for bacterial outer membrane lipid biosynthesis. The present review intends to draw attention to the role of mgrB chromosomal mutations in membrane permeability in K. pneumoniae that confer colistin resistance. With growing concern regarding the global emergence of colistin resistance, deciphering physical changes of the resistant membrane mediated by mgrB inactivation may provide new insights for the discovery of novel antimicrobials that are highly effective at membrane penetration, in addition to finding out how this can help in alleviating the resistance situation.

High prevalence of mgrB-mediated colistin resistance among carbapenem-resistant Klebsiella pneumoniae is associated with biofilm formation, and can be overcome by colistin-EDTA combination therapy

The global prevalence of colistin-resistant Klebsiella pneumoniae (ColRkp) facilitated by chromosomal and plasmid-mediated Ara4N or PEtN-remodeled LPS alterations has steadily increased with increased colistin usage for treating carbapenem-resistant K. pneumoniae (CRkp). Our study demonstrated the rising trend of ColRkp showing extensively and pandrug-resistant characteristics among CRkp, with a prevalence of 28.5%, which was mediated by chromosomal mgrB, pmrB, or phoQ mutations (91.5%), and plasmid-mediated mcr-1.1, mcr-8.1, mcr-8.2 alone or in conjunction with R256G PmrB (8.5%). Several genetic alterations in mgrB (85.1%) with increased expressions of Ara4N-related phoPQ and pmrK were critical for establishing colistin resistance in our isolates. In this study, we discovered the significant associations between extensively drug-resistant bacteria (XDR) and pandrug-resistant bacteria (PDR) ColRkp in terms of moderate, weak or no biofilm-producing abilities, and altered expressions of virulence factors. These ColRkp would therefore be very challenging to treat, emphasizing for innovative therapy to combat these infections. Regardless of the underlying colistin-resistant mechanisms, colistin-EDTA combination therapy in this study produced potent synergistic effects in both in vitro and in vivo murine bacteremia, with no ColRkp regrowth and improved animal survival, implying the significance of colistin-EDTA combination therapy as systemic therapy for unlocking colistin resistance in ColRkp-associated bacteremia.

Prevalence, Characteristics, and Clonal Distribution of Escherichia coli Carrying Mobilized Colistin Resistance Gene mcr-1.1 in Swine Farms and Their Differences According to Swine Production Stages

Global spread of Escherichia coli strains carrying the mobilized colistin resistance gene mcr-1.1 (MCR1-EC) poses serious threats to public health. Colistin has been generally prescribed for swine colibacillosis, having made swine farms as major reservoirs of MCR1-EC. The present study aimed to understand characteristic differences of MCR1-EC, including prevalence, antimicrobial resistance, and virulence, according to swine production stages. In addition, genetic relatedness was evaluated between MCR1-EC isolated from this study as well as pig-, human-, and chicken-derived strains published in the National Center for Biotechnology Information (NCBI), based on the multi-locus sequence types (MLSTs) and whole-genome sequences (WGS). Individual fecal samples (n = 331) were collected from asymptomatic weaning-piglets, growers, finishers, and sows from 10 farrow-to-finishing farms in South Korea between 2017 and 2019. The weighted prevalence of MCR1-EC was 11.6% (95% CI: 8.9%–15.0%, 55/331), with the highest prevalence at weaning stage. The 96.2% of MCR1-EC showed multi-drug resistance. Notably, weaning stage-derived MCR1-EC showed higher resistance rates (e.g., against extended-spectrum β-lactams or quinolones) than those from other stages. MCR1-EC with virulence advantages (e.g., intestinal/extraintestinal pathogenic E. coli or robust biofilm formation) were identified from all pig stages, accounting for nearly half of the total strains. WGS-based in-depth characterization showed that intestinal pathogenic MCR1-EC harbored multi-drug resistance and multiple virulence factors, which were highly shared between strains isolated from pigs of different stages. The clonal distribution of MCR1-EC was shared within swine farms but rarely across farms. The major clonal type of MCR1-EC from swine farms and NCBI database was ST10-A. Core genomes of MCR1-EC isolated from individuals within closed environments (same farms or human hospitals) were highly shared (genetic distance < 0.01), suggesting a high probability of clonal expansion of MCR1-EC within closed environments such as livestock husbandry. To the best of our knowledge, this is the first study to analyze the differences in the characteristics and clonal distribution of MCR1-EC according to production stages in swine farms, an important reservoir of MCR1-EC. Our results highlight the need to establish MCR1-EC control plans in swine farms based on an in-depth understanding of MCR1-EC characteristics according to swine production stages, focusing especially on the weaning stages.

Phenotypic and molecular characterization of β-lactamase and plasmid-mediated quinolone resistance genes in Klebsiella oxytoca isolated from slaughtered pigs in Thailand

Background and Aim:

Over recent years, antimicrobial-resistant Klebsiella species in humans, animals, food animals, food products, and agricultural environments have been the center of attention due to its role in the evolution of antimicrobial resistance. The emergence of resistance to fluoroquinolones and cephalosporins of third and higher generations in Klebsiella oxytoca has not received much attention in animal husbandry compared to that in Klebsiella pneumoniae. Reports on K. oxytoca are limited in the study area. Therefore, we investigated the antimicrobial susceptibility and resistance genes in K. oxytoca isolated from slaughtered pigs in Thailand.

Materials and Methods:

Microbiological examination was conducted on 384 Klebsiella spp. isolates recovered from slaughtered pigs in ten provinces of Thailand. Seventy-two K. oxytoca isolates (18.75%) were examined for antimicrobial-resistant genes (β-lactamase [bla_TEM, bla_CTX-M, and bla_SHV]) and fluoroquinolone-resistant genes (qnrA, qnrB, qnrC, qnrD, qnrS, oqxAB, aac(6’)-Ib-cr, and qepA).

Results:

The most common genotype was bla_CTX-M (58/72, 80.55%), followed by bla_TEM with bla_CTX-M (7/72, 9.72%) and bla_TEM (6/72, 8.33%). The most common bla_CTX-M group was bla_CTX-M-1 (19/58, 32.76%), followed by bla_CTX-M-9 (1/58, 1.72%). Plasmid-mediated quinolone resistance genes were identified in 13 (18.05%) isolates: qnrS (16.70%) and qnrB (1.4%). All 13 isolates had qnrS transferable to an Escherichia coli recipient, whereas qnrB was not detected in any transconjugants. Either bla_CTX-M or bla_TEM harbored by one K. oxytoca strain was transferable to an E. coli recipient. Analysis of antimicrobial susceptibility revealed that more than 90% of the bla_CTX-M-carrying K. oxytoca isolates were susceptible to chloramphenicol, trimethoprim, ceftazidime, cefepime, cefotaxime, amoxicillin-clavulanic acid, piperacillin–tazobactam, and fosfomycin. All K. oxytoca isolates (13) harboring qnr were susceptible to carbapenem and ceftriaxone; however, 43 (74.13%) of the K. oxytoca isolates harboring bla_CTX-M exhibited extended-spectrum β-lactamase activity. Most of the K. oxytoca isolates from pigs were highly resistant to ampicillin, azithromycin, and gentamicin.

Conclusion:

To prevent further transmission of Klebsiella spp. Between food animals and humans, strict control of antibiotic use in clinical and livestock settings is necessary along with routine disinfection of the livestock environment and efforts to increase awareness of antimicrobial resistance transmission.