The presence of colistin resistance gene mcr-1 and -3 in ESBL producing Escherichia coli isolated from food in Ho Chi Minh City, Vietnam

Abundance of Colistin-Resistance Genes in Retail Meats in Vietnam

The degree of contamination of retail meat with colistin-resistant bacteria and its potential contribution to dissemination within communities remains to be determined. Thus, we aimed to elucidate the contamination status of colistin-resistance genes, indicative of colistin-resistant bacteria, in retail meats in Vietnam. In total, 46 chicken and 49 pork meats from stores in Vietnam and Japan were examined. Multiplex real-time polymerase chain reaction with TaqMan probes was performed for detecting mcr-1, mcr-3, and Escherichia coli 16S rRNA. Colistin-resistant bacteria in meats were isolated using selective media. The minimum inhibitory concentrations of colistin were determined using the broth microdilution method. The results showed that 70.7% of chicken meats in Vietnam were contaminated with both mcr-1 and mcr-3. Meanwhile, mcr-1 and mcr-3 were detected in 15.9% and 40.9% of pork meat, respectively. Only mcr-3 was detected in 40% of chicken in Japan. In addition, mcr-1-harboring E. coli and mcr-3-harboring Aeromonas were isolated from chicken meats in Vietnam. Some of these isolates showed colistin resistance. These results showed that most retail meats were highly contaminated with colistin-resistance genes. Notably, our results suggest that mcr-3 is more prevalent in the contaminated samples compared with mcr-1.

A Review on Colistin Resistance: An Antibiotic of Last Resort

Antibiotic resistance has emerged as a significant global public health issue, driven by the rapid adaptation of microorganisms to commonly prescribed antibiotics. Colistin, previously regarded as a last-resort antibiotic for treating infections caused by Gram-negative bacteria, is increasingly becoming resistant due to chromosomal mutations and the acquisition of resistance genes carried by plasmids, particularly the mcr genes. The mobile colistin resistance gene (mcr-1) was first discovered in E. coli from China in 2016. Since that time, studies have reported different variants of mcr genes ranging from mcr-1 to mcr-10, mainly in Enterobacteriaceae from various parts of the world, which is a major concern for public health. The co-presence of colistin-resistant genes with other antibiotic resistance determinants further complicates treatment strategies and underscores the urgent need for enhanced surveillance and antimicrobial stewardship efforts. Therefore, understanding the mechanisms driving colistin resistance and monitoring its global prevalence are essential steps in addressing the growing threat of antimicrobial resistance and preserving the efficacy of existing antibiotics. This review underscores the critical role of colistin as a last-choice antibiotic, elucidates the mechanisms of colistin resistance and the dissemination of resistant genes, explores the global prevalence of mcr genes, and evaluates the current detection methods for colistin-resistant bacteria. The objective is to shed light on these key aspects with strategies for combating the growing threat of resistance to antibiotics.

Comparative genome analysis of colistin-resistant Escherichia coli harboring mcr isolated from rural community residents in Ecuador and Vietnam

The spread of colistin-resistant bacteria among rural community residents of low- and middle-income countries is a major threat to community health. Although the mechanism of the spread of colistin-resistant bacteria in communities is unknown, geographic and regional characteristics may influence it. To elucidate the spread mechanism of colistin-resistant bacteria, we analyzed the genomes of colistin-resistant Escherichia coli isolated from Vietnam and Ecuador residents, which are geographically and socially different. Stool specimens of 139 and 98 healthy residents from Ecuador and Vietnam rural communities, respectively, were analyzed for colistin-resistant E. coli with mcr. Its prevalence in the residents of all the communities assessed was high and approximately equal in both countries: 71.8% in Ecuador and 69.4% in Vietnam. A phylogenetic tree analysis revealed that the sequence type of colistin-resistant E. coli was diverse and the major sequence types were different between the two countries. The location of mcr in the isolates showed that the proportion of chromosomal mcr was 35.1% and 8.5% in the Vietnam and Ecuador isolates, respectively. Most of these chromosomal mcr genes (75%-76%) had an intact mcr-transposon Tn6330. Contrastingly, the replicon types of the mcr-carrying-plasmids were diverse in both countries, but almost all belonged to IncI2 in Ecuador and IncX1/X4 in Vietnam. Approximately 26%-45% of these mcr-plasmids had other resistance genes, which also varied between countries. These results suggest that although the overall profile of the colistin-resistant E. coli isolates is diverse in these countries, the phylogenesis of the isolates and mcr-carrying plasmids has regional characteristics. Although the contributing factors are not clear, it is obvious that the overall profile of colistin-resistant bacteria dissemination varies between countries. Such different epidemic patterns are important for establishing country-specific countermeasures against colistin-resistant bacteria.

Impact of antimicrobial use on abundance of antimicrobial resistance genes in chicken flocks in Vietnam

Objectives

We investigated longitudinally Vietnamese small-scale chicken flocks in order to characterize changes in antimicrobial resistance gene (ARG) content over their life cycle, and the impact of antimicrobial use (AMU) on an intervention consisting of veterinary advice provision.

Methods

AMU data and faecal samples were collected from 83 flocks (25 farms) at day-old, mid- and late-production (∼4 month cycle). Using high-throughput real-time PCR, samples were investigated for 94 ARGs. ARG copies were related to 16S rRNA and ng of DNA (ngDNA). Impact of AMU and ARGs in day-olds was investigated by mixed-effects models.

Results

Flocks received a mean (standard error, SE) animal daily dose (ADD) of 736.7 (83.0) and 52.1 (9.9) kg in early and late production, respectively. Overall, ARGs/16S rRNA increased from day-old (mean 1.47; SE 0.10) to mid-production (1.61; SE 0.16), further decreasing in end-production (1.60; SE 0.1) (all P > 0.05). In mid-production, ARGs/16S rRNA increased for aminoglycosides, phenicols, sulphonamides and tetracyclines, decreasing for polymyxins β-lactams and genes that confer resistance to mutiple classes (multi-drug resistance) (MDR). At end-production, aminoglycoside resistance decreased and polymyxin and quinolone resistance increased (all P < 0.05). Results in relation to ngDNA gave contradictory results. Neither AMU nor ARGs in day-olds had an impact on subsequent ARG abundance. The intervention resulted in 74.2% AMU reduction; its impact on ARGs depended on whether ARGs/ngDNA (+14.8%) or ARGs/16S rRNA metrics (-10.7%) (P > 0.05) were computed.

Conclusions

The flocks' environment (contaminated water, feed and residual contamination) is likely to play a more important role in transmission of ARGs to flocks than previously thought. Results highlight intriguing differences in the quantification of ARGs depending on the metric chosen.

Mobile Colistin Resistance (mcr) Gene-Containing Organisms in Poultry Sector in Low- and Middle-Income Countries: Epidemiology, Characteristics, and One Health Control Strategies

Mobile colistin resistance (mcr) genes (mcr-1 to mcr-10) are plasmid-encoded genes that threaten the clinical utility of colistin (COL), one of the highest-priority critically important antibiotics (HP-CIAs) used to treat infections caused by multidrug-resistant and extensively drug-resistant bacteria in humans and animals. For more than six decades, COL has been used largely unregulated in the poultry sector in low- and middle-income countries (LMICs), and this has led to the development/spread of mcr gene-containing bacteria (MGCB). The prevalence rates of mcr-positive organisms from the poultry sector in LMICs between January 1970 and May 2023 range between 0.51% and 58.8%. Through horizontal gene transfer, conjugative plasmids possessing insertion sequences (ISs) (especially ISApl1), transposons (predominantly Tn6330), and integrons have enhanced the spread of mcr-1, mcr-2, mcr-3, mcr-4, mcr-5, mcr-7, mcr-8, mcr-9, and mcr-10 in the poultry sector in LMICs. These genes are harboured by Escherichia, Klebsiella, Proteus, Salmonella, Cronobacter, Citrobacter, Enterobacter, Shigella, Providencia, Aeromonas, Raoultella, Pseudomonas, and Acinetobacter species, belonging to diverse clones. The mcr-1, mcr-3, and mcr-10 genes have also been integrated into the chromosomes of these bacteria and are mobilizable by ISs and integrative conjugative elements. These bacteria often coexpress mcr with virulence genes and other genes conferring resistance to HP-CIAs, such as extended-spectrum cephalosporins, carbapenems, fosfomycin, fluoroquinolone, and tigecycline. The transmission routes and dynamics of MGCB from the poultry sector in LMICs within the One Health triad include contact with poultry birds, feed/drinking water, manure, poultry farmers and their farm workwear, farming equipment, the consumption and sale of contaminated poultry meat/egg and associated products, etc. The use of pre/probiotics and other non-antimicrobial alternatives in the raising of birds, the judicious use of non-critically important antibiotics for therapy, the banning of nontherapeutic COL use, improved vaccination, biosecurity, hand hygiene and sanitization, the development of rapid diagnostic test kits, and the intensified surveillance of mcr genes, among others, could effectively control the spread of MGCB from the poultry sector in LMICs.

The highly diverse plasmid population found in Escherichia coli colonizing travellers to Laos and its role in antimicrobial resistance gene carriage

Increased colonization by antimicrobial-resistant organisms is closely associated with international travel. This study investigated the diversity of mobile genetic elements involved with antimicrobial resistance (AMR) gene carriage in extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli that colonized travellers to Laos. Long-read sequencing was used to reconstruct complete plasmid sequences from 48 isolates obtained from the daily stool samples of 23 travellers over a 3 week period. This method revealed a collection of 105 distinct plasmids, 38.1 % (n=40) of which carried AMR genes. The plasmids in this population were diverse, mostly unreported and included 38 replicon types, with F-type plasmids (n=23) the most prevalent amongst those carrying AMR genes. Fine-scale analysis of all plasmids identified numerous AMR gene contexts and emphasized the importance of IS elements, specifically members of the IS6/IS26 family, in the evolution of complex multidrug resistance regions. We found a concerning convergence of ESBL and colistin resistance determinants, with three plasmids from two different F-type lineages carrying bla CTX-M and mcr genes. The extensive diversity seen here highlights the worrying probability that stable new vehicles for AMR will evolve in E. coli populations that can disseminate internationally through travel networks.

The conjugative transfer of plasmid-mediated mobile colistin resistance gene, mcr-1, to Escherichia coli O157:H7 and Escherichia coli O104:H4 in nutrient broth and in mung bean sprouts

The emergence of mobile colistin resistant gene (mcr-1) in Enterobacteriaceae has become a global public health concern. Dissemination of the mcr-1 gene through conjugation of bacteria associated with food may occur. This research investigated the transfer frequency of the mcr-1 gene among Escherichia coli in liquid media and during growth of mung bean sprouts. The donor strain E. coli NCTC 13846 (mcr-1 positive) and recipient strains of E. coli O157:H7 and E. coli O104:H4 were used. Mating experiments in vitro were conducted at 4, 25, and 37 °C for up to 36 h. The in vivo mating experiments (growing sprouts) were conducted in a sprout growth chamber with irrigation of 1 min/h over 6 days following inoculation of mung bean seeds with the donor and a recipient. The highest transfer frequencies in TSB media, 2.86E-07 and 3.24E-07, occurred at 37 °C after mating for 24 h for E. coli O104:H4 and E. coli O157:H7, respectively. Transconjugants were not detected in liquid media at 4 °C. Moreover, transfer frequency (5.68E-05 per recipient) of mcr-1 was greater during mung bean sprout growth for E. coli O104:H4 compared to E. coli O157:H7 (1.02E-05 per recipient) Day 3 to Day 6. This study indicates that the transfer of antibiotic resistant gene(s) among bacteria during mung bean sprout production may facilitate the spread of antibiotic resistant bacteria in the environment and to humans.

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.

P, Molina CA, Castillejo P. Beta-Lactam Antibiotic Resistance Genes in the Microbiome of the Public Transport System of Quito, Ecuador

Multidrug-resistant bacteria present resistance mechanisms against β-lactam antibiotics, such as Extended-Spectrum Beta-lactamases (ESBL) and Metallo-β-lactamases enzymes (MBLs) which are operon encoded in Gram-negative species. Likewise, Gram-positive bacteria have evolved other mechanisms through mec genes, which encode modified penicillin-binding proteins (PBP2). This study aimed to determine the presence and spread of β-lactam antibiotic resistance genes and the microbiome circulating in Quito's Public Transport (QTP). A total of 29 station turnstiles were swabbed to extract the surface environmental DNA. PCRs were performed to detect the presence of 13 antibiotic resistance genes and to identify and to amplify 16S rDNA for barcoding, followed by clone analysis, Sanger sequencing, and BLAST search. ESBL genes bla_TEM-1 and bla_CTX-M-1 and MBL genes bla_OXA-181 and mecA were detected along QPT stations, blaTEM being the most widely spread. Two subvariants were found for bla_TEM-1, bla_CTX-M-1, and bla_OXA-181. Almost half of the circulating bacteria found at QPT stations were common human microbiota species, including those classified by the WHO as pathogens of critical and high-priority surveillance. β-lactam antibiotic resistance genes are prevalent throughout QPT. This is the first report of bla_OXA-181 in environmental samples in Ecuador. Moreover, we detected a new putative variant of this gene. Some commensal coagulase-negative bacteria may have a role as mecA resistance reservoirs.

Colistin resistance in Escherichia coli and Klebsiella pneumoniae in humans and backyard animals in Ecuador

Objective

Colistin is an antibiotic of last resort for treating serious Gram-negative bacterial infections. However, the misuse of colistin, especially as an animal growth promoter, has contributed to increasing antimicrobial resistance, mediated mainly through plasmid transfer of the mcr-1 gene. This study assessed the prevalence of phenotypic and molecular colistin resistance in Escherichia coli and Klebsiella pneumoniae in Ecuador in healthy humans and their chickens and pigs.

Methods

Fecal samples were collected from humans and their chickens and pigs in two rural coastal and Amazon regions between April and August 2020. Gram-negative bacteria were isolated and identified using conventional techniques. Phenotypic resistance was determined using the broth microdilution technique, and the mcr-1 gene was detected using conventional polymerase chain reaction.

Results

A total of 438 fecal samples were obtained from 137 humans, 147 pigs and 154 chickens. The prevalence of E. coli isolates was 86.3% (378/438) and K. pneumoniae, 37.4% (164/438). Overall, the mcr-1 gene was found in 90% (340/378) of E. coli isolates, with higher prevalences found in isolates from coastal regions (96.5%, 191/198), humans (95.6%, 111/116) and chickens (91.8%, 123/134); for K. pneumoniae, the gene was found in 19.5% (32/164) of isolates, with equal distribution between regions and hosts. Only four isolates, two E. coli and two K. pneumoniae, showed phenotypic resistance: mcr-1 was present in both E. coli strains but absent in the K. pneumoniae strains.

Conclusions

Despite a low prevalence of phenotypic resistance to colistin, the high prevalence of the mcr-1 gene in E. coli is of concern. Ecuador's ban on using colistin in animal husbandry must be enforced, and continual monitoring of the situation should be implemented.

Emergence and Dissemination of Extraintestinal Pathogenic High-Risk International Clones of Escherichia coli

Multiresistant Escherichia coli has been disseminated worldwide, and it is one of the major causative agents of nosocomial infections. E. coli has a remarkable and complex genomic plasticity for taking up and accumulating genetic elements; thus, multiresistant high-risk clones can evolve. In this review, we summarise all available data about internationally disseminated extraintestinal pathogenic high-risk E. coli clones based on whole-genome sequence (WGS) data and confirmed outbreaks. Based on genetic markers, E. coli is clustered into eight phylogenetic groups. Nowadays, the E. coli ST131 clone from phylogenetic group B2 is the predominant high-risk clone worldwide. Currently, strains of the C1-M27 subclade within clade C of ST131 are circulating and becoming prominent in Canada, China, Germany, Hungary and Japan. The C1-M27 subclade is characterised by bla_CTX-M-27. Recently, the ST1193 clone has been reported as an emerging high-risk clone from phylogenetic group B2. ST38 clone carrying bla_OXA-244 (a bla_OXA-48-like carbapenemase gene) caused several outbreaks in Germany and Switzerland. Further high-risk international E. coli clones include ST10, ST69, ST73, ST405, ST410, ST457. High-risk E. coli strains are present in different niches, in the human intestinal tract and in animals, and persist in environment. These strains can be transmitted easily within the community as well as in hospital settings. WGS analysis is a useful tool for tracking the dissemination of resistance determinants, the emergence of high-risk mulitresistant E. coli clones and to analyse changes in the E. coli population on a genomic level.

Frequent contamination of edible freshwater fish with colistin-resistant Escherichia coli harbouring the plasmid-mediated mcr-1 gene

The threat of antimicrobial resistance is increasing. Microbial food contamination poses a serious public health risk; however, there are only a few studies on the prevalence of colistin-resistant Escherichia coli (COL-E) contamination in freshwater fish. This study aimed to characterise the antibiotic resistance genes and antibiotic susceptibility profiles of COL-E in freshwater fish in Vietnam. In total, 103 fish were collected and 63 COL-E were isolated. COL-E was investigated by genotyping mcr and AmpC/extended-spectrum β-lactamase (ESBL)-related genes. The results show that COL-E and AmpC/ESBL-producing COL-E were confirmed in 24.3 % and 14.6 % of the fish, respectively. Multiplex PCR for mcr-1-9 showed that all 63 COL-E harboured mcr-1, while mcr-3 was detected in 7.9 % of COL-E. The minimum inhibitory concentration of colistin ranged from 2 to 256 μg/mL. Meanwhile, antibiotic susceptibility results show that all COL-E were resistant to ampicillin, streptomycin, and chloramphenicol.

Genomic epidemiological analysis of mcr-1-harboring Escherichia coli collected from livestock settings in Vietnam

Livestock has been implicated as a reservoir for antimicrobial resistance (AMR) genes that can spread to humans when antimicrobials are used in animals for food production to treat clinical diseases and prevent and control common disease events. In Vietnam, mcr-1-harboring Escherichia coli (MCRPEC) strains have been isolated from humans, animals (chickens, pigs, and dogs) feces, flies, foods, and the environment (rainwater, well water, and irrigation water) in communities and from clinical specimens in hospitals. The relationship between levels of AMR in livestock and its occurrence in humans is complex and is driven by many factors. We conducted whole genome sequencing of MCRPEC to analyze the molecular epidemiological characteristics, history, and relatedness of 50 isolates obtained in 2019 from different reservoirs in farms and markets in Ha Nam province, Vietnam. 34 sequence types (STs) with 3 new STs were identified in multilocus sequence typing analysis: ST12945 and ST12946 from chicken feces, and ST12947 from flies. The AMR phenotypes of 50 MCRPEC isolates were as follows: ampicillin (100%, 50/50), cefotaxime (10%, 5/50), gentamicin (60%, 30/50), amikacin (8%, 4/50), meropenem (6%, 3/50), ceftazidime (18%, 9/50), colistin (24%, 12/50) and ciprofloxacin (80%, 40/50). All 50 MCRPEC isolates were identified as MDR. 100% (50/50) isolates carried AMR genes, ranging from 5 to 22 genes. The most prevalent plasmid replicon types carrying mcr-1 were IncP-1 (17/37, 45.9%), IncX4 (7/37, 18.9%), and IncHI2/IncHI2A (6/37, 16.2%). These data suggest that the epidemiology of the mcr-1 gene is mostly determined by plasmid spreading instead of clonal dissemination of MCRPE strains. The co-occurrence of several STs such as ST10, ST48, ST155, ST206, ST2705 in various sample types, joined to the higher prevalence of a few types of Inc plasmids, confirms the dissemination of the mcr-1 carrying plasmids in E. coli clones established in livestock. 5 over 8 STs identified in flies (ST206, ST2705, ST155, ST10, and ST48) suggested the fly contribution in the transmission of AMR bacteria in environments. These popular STs also occur in human samples and 100% of the human samples were positive for the mcr-1 gene.

Genomic Analysis of a mcr-9.1-Harbouring IncHI2-ST1 Plasmid from Enterobacter ludwigii Isolated in Fish Farming

This study analyzed the resistome, virulome and mobilome of an MCR-9-producing Enterobacter sp. identified in a muscle sample of seabream (Sparus aurata), collected in a land tank from multitrophic fish farming production. Average Nucleotide Identity analysis identified INSAq77 at the species level as an Enterobacter ludwigii INSAq77 strain that was resistant to chloramphenicol, florfenicol and fosfomycin and was susceptible to all other antibiotics tested. In silico antimicrobial resistance analyses revealed genes conferring in silico resistance to β-lactams (bla_ACT-88), chloramphenicol (catA4-type), fosfomycin (fosA2-type) and colistin (mcr-9.1), as well as several efflux pumps (e.g., oqxAB-type and mar operon). Further bioinformatics analysis revealed five plasmid replicon types, including the IncHI2/HI2A, which are linked to the worldwide dissemination of the mcr-9 gene in different antibiotic resistance reservoirs. The conserved nickel/copper operon rcnR-rcnA-pcoE-ISSgsp1-pcoS-IS903-mcr-9-wbuC was present, which may play a key role in copper tolerance under anaerobic growth and nickel homeostasis. These results highlight that antibiotic resistance in aquaculture are spreading through food, the environment and humans, which places this research in a One Health context. In fact, colistin is used as a last resort for the treatment of serious infections in clinical settings, thus mcr genes may represent a serious threat to human health.

Modelling the impact of antimicrobial use and external introductions on commensal E. coli colistin resistance in small-scale chicken farms of the Mekong delta of Vietnam

Colistin is a critically important antimicrobial for human medicine, and colistin-resistant Escherichia coli are commonly found in poultry and poultry products in Southeast Asia. Here, we aim at disentangling the within-farm and outside-farm drivers of colistin resistance in small-scale chicken farms of the Mekong delta of Vietnam. Nineteen Vietnamese chicken farms were followed up along a whole production cycle, during which weekly antimicrobial use data were recorded. At the beginning, middle and end of each production cycle, commensal E. coli samples from birds were collected, pooled and tested for colistin resistance. Twelve models were fitted to the data using an expectation-maximization algorithm and compared. We further tested the spatial clustering of the occurrence of resistance importations from external sources using the local Moran's I statistic. In the best model, colistin resistance in E. coli from chickens was found to be mostly affected by importations of resistance, and, to a lesser extent, by the use of antimicrobials in the last 1.73 weeks [0.00; 2.90], but not by the use of antimicrobials in day-olds, nor their colistin resistance carriage from hatchery. The occurrence of external source importations proved to be sometimes spatially clustered, suggesting a role of local environmental sources of colistin resistance.

The prevalence, antibiotic resistance and multilocus sequence typing of colistin-resistant bacteria isolated from Penaeus vannamei farms in earthen ponds and HDPE film-lined ponds in China

The aquaculture environment, especially the culture ponds and aquaculture products, is considered to be an important reservoir of colistin resistance genes. However, systematic investigations of colistin resistance in Penaeus vannamei farming in different culture modes are scarce. In this study, a total of 93 non-duplicated samples were collected from P. vannamei farms in five cities in China from 2019 to 2021. The prevalence, antibiotic resistance and multilocus sequence typing (MLST) of colistin-resistant bacteria were measured and analysed. The results showed that among the 1601 isolates in P. vannamei and its environmental samples, the pollution of colistin-resistant bacteria was serious (the overall prevalence was 37.3% and 28.8%, respectively), regardless of the earthen pond or high-density polyethylene (HDPE) film-lined pond. Among 533 isolates, the prevalence of mobile colistin resistance (mcr) genes, mcr-1, was the highest (60%, 320/533), followed by mcr-4 (1.5%, 8/533), mcr-8 (0.9%, 5/533), mcr-10 (0.6%, 3/533) and mcr-7 (0.4%, 2/533). The prevalence of mcr-1 in earthen ponds was significantly higher than that in HDPE film-lined ponds (67.5% vs. 49.1%, p < .001). The dominant strain carrying mcr-1 was Bacillus spp. (54.1%, 173/320), followed by Enterobacter spp. (8.1%, 26/320), Staphylococcus spp. (6.3%, 20/320) and Aeromonas spp. (5.3%, 17/320). The antibiotic resistance profiles of 173 Bacillus spp. varied among different sampling locations and culture types. These isolates were highly resistant to cefepime, ceftriaxone, trimethoprim-sulfamethoxazole and ceftiofur (>45%), and multidrug-resistant isolates were common (62.4%, 108/173). Sequence type (ST) 26 (37/66, 56%) was found to be the most prevalent ST in mcr-1-positive Bacillus cereus isolated from the aquaculture environment. In summary, our study pointed out that it is necessary to continuously monitor antibiotic usage and its residues regardless of the pond types, especially with regard to critical drugs such as colistin.

Worldwide Prevalence of mcr-mediated Colistin-Resistance Escherichia coli in Isolates of Clinical Samples, Healthy Humans, and Livestock-A Systematic Review and Meta-Analysis

Background: Antimicrobial resistance is a serious public-health problem throughout the world. Escherichia coli, the most common Gram-negative microorganism, has developed different resistance mechanisms, making treating infections difficult. Colistin is considered a last-resort drug in the treatment of infections caused by E. coli. Plasmid-mediated mobile-colistin-resistant (mcr) genes in E. coli, now disseminated globally, are considered a major public-health threat. Humans, chickens, and pigs are the main reservoirs for E. coli and the sources of antibiotic resistance. Hence, an up-to-date and precise estimate of the global prevalence of mcr resistance genes in these reservoirs is necessary to understand more precisely the worldwide spread and to more effectively implement control and prevention strategies. Methodology: Publications were identified in the PubMed database on the basis of the PRISMA guidelines. English full-text articles were selected from December 2014 to March 2021. Descriptive statistics and a meta-analysis were performed in Excel and R software, respectively. Colistin resistance was defined as the molecular-genetic detection of the mcr genes. The crude and estimated prevalence were calculated for each host and continent. The studies were divided into two groups; community-based when they involved isolates from healthy humans, chickens, or pigs, and clinical studies when they involved only hospital, outpatient, or laboratory isolates. Results: A total of 1278 studies were identified and 218 were included in this systematic review and meta-analysis, divided into community studies (159 studies) and clinical studies (59 studies). The general prevalence of mcr-mediated colistin-resistant E. coli (mcrMCRE) was 6.51% (n = 11,583/177,720), reported in 54 countries and on five continents; Asia with 119 studies followed by Europe with 61 studies registered the most articles. Asia reported the major diversity of mcr-variants (eight of nine, except mcr-2). Worldwide, chickens and pigs proved to be the principal reservoir of mcr with an estimated prevalence of 15.8% and 14.9%, respectively. Healthy humans and clinical isolates showed a lower prevalence with 7.4% and 4.2% respectively. Conclusions: In this systematic review and meta-analysis, the worldwide prevalence of mcr in E. coli isolated from healthy humans, chickens, and pigs was investigated. A wide prevalence and distribution of mcr genes was demonstrated on all continents in E. coli isolates from the selected reservoirs. Understanding the epidemiology and occurrence in the reservoirs of mcr in E. coli on different continents of the world facilitates tracing how mcr genes are transmitted and determining the infection risks for humans. This knowledge can be used to reduce the incidence of zoonotic transmission by implementing the appropriate control programs.

Genomic characterization of antimicrobial resistance in mcr-carrying ESBL-producing Escherichia coli from pigs and humans

Whole-genome sequencing (WGS) was conducted to characterize mcr-carrying extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli (n=7). These E. coli isolates originated from two pigs (TH2 and TH3) and two humans (TH8 and TH9) from Thailand, and three pigs from Lao PDR (LA1, LA2 and LA3). Four E. coli sequence types/serotypes - ST6833/H20 (TH2 and TH3), ST48/O160:H40 (TH8 and TH9), ST5708/H45 (LA1) and ST10562/O148:H30 (LA2 and LA3) - were identified. The plasmid replicon type IncF was identified in all isolates. The point mutations Ser31Thr in PmrA and His2Arg in PmrB were found concurrently in all isolates (colistin MIC=4-8 µg ml^-1). LA1 contained up to five point mutations in PmrB, and the colistin MIC was not significantly different from that for the other isolates. All mcr-1.1 was located in the ISApl1-mcr-1-pap2 element, while all mcr-3.1 was located in the TnAs2-mcr-3.1-dgkA-ISKpn40 element. The mcr-3.1 and bla _CTX-M-55 genes were co-localized on the same plasmid, which concurrently contained cml, qnrS1 and tmrB. The bla _CTX-M-55 and mcr-3.1 genes were located on conjugative plasmids and could be transferred horizontally under selective pressure from ampicillin or colistin. In conclusion, comprehensive insights into the genomic information of ESBL-producing E. coli harbouring mcr were obtained. As mcr-carrying ESBL-producing E. coli were detected in pigs and humans, a holistic and multisectoral One Health approach is required to contain antimicrobial resistance (AMR).

Removal of Extended-Spectrum Beta-Lactamase-Producing Escherichia coli, ST98, in Water for Human Consumption by Black Ceramic Water Filters in Low-Income Ecuadorian Highlands

Fecal contamination in natural water sources is a common problem in low-income countries. Several health risks are associated with unprotected water sources, such as gastrointestinal infections caused by parasites, viruses, and bacteria. Moreover, antibiotic-resistant bacteria in water sources have become an increasing problem worldwide. This study aimed to evaluate the bacterial pathogens present in water within a rural context in Ecuador, along with the efficiency of black ceramic water filters (BCWFs) as a sustainable household water treatment. We monitored five natural water sources that were used for human consumption in the highlands of Ecuador and analyzed the total coliforms and E. coli before and after BCWF installation. The results indicated a variable bacterial contamination (29–300 colony-forming units/100mL) in all unfiltered samples, and they were considered as high risk for human consumption, but after filtration, no bacteria were present. Moreover, extended-spectrum beta-lactamase-producing E. coli with bla_TEM, bla_CTX-M9, and bla_CTX-M1 genes, and two E. coli classified in the clonal complex ST10 (ST98) were detected in two of the locations sampled; these strains can severely impact public health. The clonal complex ST10, found in the E. coli isolates, possesses the potential to spread bacteria-resistant genes to humans and animals. The results of the use of BCWFs, however, argue for the filters’ potential impact within those contexts, as the BCWFs completely removed even antibiotic-resistant contaminants from the water.

The emergence of CTX-M-55 in ESBL-producing Escherichia coli from vegetables sold in local markets of northern Thailand

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli are spreading worldwide and pose a public health issue. An assessment of their presence in the environment and in food chain products would clarify the pathway of this foodborne transmission. Here, we investigated the prevalence of ESBL-producing E. coli in fresh vegetables purchased from fresh markets in Chiang Rai, Thailand. Overall, 8.8% of the samples collected contained ESBL-producing E. coli, of which 81.3% were multidrug-resistant. All isolates carried the bla_CTX-M-55 gene, and 10 isolates contained the ISEcp1 gene. One E. coli strain carried bla_CTX-M-55 coexisting with bla_TEM-1. Thirteen different sequence types (ST48, ST101, ST155, ST165, ST398, ST414, ST457, ST515, ST542, ST1081, ST3045, ST7538 and ST10651) were identified. One strain belonged to ST101, which is one of the most prevalent STs among human isolates. Our study thus demonstrated the spread of CTX-M-55 on non-ST131 vegetable isolates that are not global pandemic strains and suggests that they may be a source of antibiotic resistance gene transfer from agricultural foods to humans. Further studies are needed to investigate the possibility that these ESBL producers could transfer resistance genes to commensal E. coli and cause severe disease.

Colistin Resistant mcr Genes Prevalence in Livestock Animals (Swine, Bovine, Poultry) from a Multinational Perspective. A Systematic Review

The objective of this review is to collect and present the results of relevant studies on an international level, on the subject of colistin resistance due to mcr genes prevalence in livestock animals. After a literature search, and using PRISMA guidelines principles, a total of 40 swine, 16 bovine and 31 poultry studies were collected concerning mcr-1 gene; five swine, three bovine and three poultry studies referred to mcr-2 gene; eight swine, one bovine, two poultry studies were about mcr-3 gene; six swine, one bovine and one poultry manuscript studied mcr-4 gene; five swine manuscripts studied mcr-5 gene; one swine manuscript was about mcr-6, mcr-7, mcr-8, mcr-9 genes and one poultry study about mcr-10 gene was found. Information about colistin resistance in bacteria derived from animals and animal product foods is still considered limited and that should be continually enhanced; most of the information about clinical isolates are relative to enteropathogens Escherichia coli and Salmonella spp. This review demonstrates the widespread dispersion of mcr genes to livestock animals, indicating the need to further increase measures to control this important threat for public health issue.

Antimicrobial-Resistant Escherichia coli Strains and Their Plasmids in People, Poultry, and Chicken Meat in Laos

Antimicrobial resistant (AMR) Enterobacterales are widely distributed among the healthy population of the Indochinese peninsula, including Laos. However, the local reservoir of these pathogens are currently not known and possible sources such as agricultural settings and food have rarely been analyzed. In this work, we investigated the extended-spectrum cephalosporin- (ESC-) and colistin-resistant Escherichia coli strains (CST-R-Ec) isolated from the gut of local people, feces of poultry, and from chicken meat (60 samples each group) in Laos. Whole-genome sequencing (WGS) analysis based on both short- and long-read sequencing approaches were implemented. The following prevalence of ESC-R-Ec and CST-R-Ec were recorded, respectively: local people (70 and 15%), poultry (20 and 23.3%), and chicken meat (21.7 and 13.3%). Core-genome analysis, coupled with sequence type (ST)/core-genome ST (cgST) definitions, indicated that no common AMR-Ec clones were spreading among the different settings. ESC-R-Ec mostly possessed bla_CTX–M–15 and bla_CTX–M–55 associated to ISEcp1 or IS26. The majority of CST-R-Ec carried mcr-1 on IncX4, IncI2, IncP1, and IncHI1 plasmids similar or identical to those described worldwide; strains with chromosomal mcr-1 or possessing plasmid-mediated mcr-3 were also found. These results indicate a high prevalence of AMR-Ec in the local population, poultry, and chicken meat. While we did not observe the same clones among the three settings, most of the bla_CTX–Ms and mcr-1/-3 were associated with mobile-genetic elements, indicating that horizontal gene transfer may play an important role in the dissemination of AMR-Ec in Laos. More studies should be planned to better understand the extent and dynamics of this phenomenon.

Isolation and plasmid characterisation of Salmonella enterica serovar Albany harbouring mcr-5 from retail chicken meat in Japan

The emergence of plasmid-mediated colistin resistance genes (mcr), which is occurring in numerous countries, is a worldwide concern, primarily because colistin is a last-resort antibiotic. Compared to E. coli, prevalence of mcr genes in Salmonella is unclear in Japan. Here we screened for mcr-1-5 genes in our collection of Salmonella strains isolated from retail meat products collected in Japan from 2012 through 2016. We found that Salmonella Albany strain 27A-368 encodes mcr-5 and that mcr genes were undetectable among the remaining 202 isolates. The resistance plasmid p27A-368 was transferred by conjugation to S. Infantis and was stably retained as a transconjugant. Whole-genome sequencing revealed that mcr-5 resided on a 115 kb plasmid (p27A-368). The plasmid backbone of p27A-368 is more similar to that of pCOV27, an ESBL-encoding plasmid recovered from avian pathogenic E. coli, rather than pSE13-SA01718 of S. Paratyphi B that encodes mcr-5. Further, mcr-5 is located on a transposon, and its sequence is similar to that of pSE13-SA01718. A phylogenetic tree based on single nucleotide variants implies a relationship between 27A-368 and S. Albany isolated in Southeast Asian countries.

Characterisation of Colistin -Resistant Enterobacterales and Acinetobacter Strains Carrying mcr Genes from Asian Aquaculture Products

Aquaculture systems are widely recognised as hotspots for horizontal gene transfer, and the need for screening for bacteria carrying antimicrobial resistance genes in aquaculture systems is becoming more important. In this study, we characterised seventeen bacterial strains (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and A. nosocomialis) resistant to colistin originating from retailed aquaculture products imported from Vietnam to the Czech Republic. The mcr-1.1 gene was found located on plasmid types IncHI2, IncI2, and IncX4, as well as on the rarely described plasmid types IncFIB-FIC and IncFIB(K), phage-like plasmid p0111, and on the chromosome of E. coli. One E. coli strain carried the mcr-3.5 gene on IncFII(pCoo) plasmid in addition to the mcr-1.1 gene located on IncHI2 plasmid. K. pneumoniae was found to carry the mcr-1.1 and mcr-8.2 genes on IncFIA(HI1) plasmid. The mcr-4.3 gene was found on similar untypeable plasmids of A. baumannii and A. nosocomialis strains, pointing to the possible interspecies transfer of plasmids carrying the mcr-4 gene. Our results highlight that some aquaculture products of Asian origin can represent an important source of variable plasmids carrying mcr genes. The results showed an involvement of phages in the incorporation of the mcr-1 gene into plasmids or the chromosome in E. coli strains from aquaculture. The detection of E. coli with the mcr-1 gene in the chromosome points to the risks associated with the stabilisation of the mcr genes in the bacterial chromosome.

Prevalence of mobile colistin resistance (mcr) genes in extended-spectrum β-lactamase-producing Escherichia coli isolated from retail raw foods in Nha Trang, Vietnam

The aim of the study was to assess the presence of genes in ESBL-producing E. coli (ESBL-Ec) isolated from retail raw food in Nha Trang, Vietnam. A total of 452 food samples comprising chicken (n = 116), pork (n = 112), fish (n = 112) and shrimp (n = 112) collected between 2015 and 2017 were examined for the prevalence of ESBL-Ec. ESBL-Ec were detected in 46.0% (208/452) of retail food samples, particularly in 66.4% (77/116), 55.4% (62/112), 42.0% (47/112) 19.6% (22/112) of chicken, pork, fish and shrimp, respectively. Sixty-five out of the 208 (31.3%) ESBL-Ec isolates were positive for mcr genes including mcr-1, mcr-3 and both mcr-1 and mcr-3 genes in 56/208 (26.9%), 1/208 (0.5%) and 8/208 (3.9%) isolates, respectively. Particularly, there was higher prevalence of mcr-1 in ESBL-Ec isolates from chicken (53.2%, 41/77) in comparison to shrimp (22.7%, 5/22), pork (11.3%, 7/62) and fish (6.4%, 3/47). mcr-3 gene was detected in co-existence with mcr-1 in ESBL-Ec isolates from shrimp (9.1%, 2/22), pork (8.1%, 5/62) and fish (2.1%, 1/47) but not chicken. The 65 mcr-positive ESBL-Ec (mcr-ESBL-Ec) were colistin-resistant with the MICs of 4-8 μg/mL. All mcr-3 gene-positive isolates belonged to group A, whereas phylogenetic group distribution of isolates harboring only mcr-1 was B1 (44.6%), A (28.6%) and D (26.8%). PFGE analysis showed diverse genotypes, although some isolates demonstrated nearly clonal relationships. S1-PFGE and Southern hybridization illustrated that the mcr-1 and mcr-3 genes were located either on chromosomes or on plasmids. However, the types of mcr genes were harbored on different plasmids with varied sizes of 30-390 kb. Besides, the ESBL genes of CTX-M-1 or CTX-M-9 were also detected to be located on plasmids. Noteworthy, co-location of CTX-M-1 with mcr-1 or mcr-3 genes on the same plasmid was identified. The conjugation experiment indicated that the mcr-1 or mcr-3 was horizontally transferable. All mcr-ESBL-Ec isolates were multidrug resistance (resistance to ≥3 antimicrobial classes). Moreover, β-Lactamase-encoding genes of the CTX-M-1 (78.5%), CTX-M-9 (21.5%), TEM (61.5%) groups were found in mcr-ESBL-Ec. The astA gene was detected in 27 (41.5%) mcr-ESBL-Ec isolates demonstrating their potential virulence. In conclusion, mcr-1 and mcr-3 genes existed individually or concurrently in ESBL-Ec isolates recovered from retail raw food in Nha Trang city, which might further complicate the antimicrobial-resistant situation in Vietnam, and is a possible health risk for human.

Quantitative Analysis of Colistin-Resistant Escherichia coli in Retail Meat from Local Vietnamese Markets

The spread of drug-resistant bacteria via food has contributed to the dissemination of resistant bacteria among humans. However, the status of food contamination with resistant bacteria, particularly the quantitative level of resistant bacteria in food, has not yet been well elucidated. In this study, the abundance of colistin-resistant Escherichia coli in meat samples was quantified to understand the origin of the contamination of meat available in local Vietnamese markets. Fifteen samples each of chicken and pork meat purchased from local Vietnamese markets were assessed for the presence of colistin-resistant E. coli with the mobile colistin resistance gene, mcr. The results showed that 40% (6/15) and 66% (10/15) of the pork and chicken meat samples, respectively, were contaminated with colistin-resistant E. coli. The median quantitative levels of colistin-resistant E. coli in the contaminated pork and chicken samples were 1.8 × 10⁴ and 4.2 × 10³ CFU/g, respectively. The results of phylogenetic analysis of isolates from a chicken meat sample showed that the contaminated colistin-resistant E. coli was a mix of multiple phylogenetical clones of bacteria that may have multiplied during sale. This is the first study to quantify the abundance of colistin-resistant E. coli in meat samples.

The Mobile Colistin Resistance Gene, mcr-1.1, Is Carried on IncX4 Plasmids in Multidrug Resistant E. coli Isolated from Rainbow Trout Aquaculture

Colistin, a last resort antibiotic, is important for controlling infections with carbapenem-resistant Enterobacteriaceae. The recent emergence of mobile-colistin-resistance (mcr) genes has threatened the effectiveness of colistin. Aquaculture is hypothesized to be a major contributor to the evolution and dissemination of mcr. However, data on mcr in aquaculture are limited. Here, the occurrence of mcr-1 was assessed in Rainbow Trout in Lebanon, a country with developing antimicrobial stewardship and an established use of colistin for medical and farming purposes. mcr-1 was detected in 5 Escherichia coli isolated from fish guts. The isolates were classified as multidrug-resistant and their colistin minimum inhibitory concentration ranged between 16 and 32 μg/mL. Whole genome sequencing analysis showed that mcr-1 was carried on transmissible IncX4 plasmids and that the isolates harbored more than 14 antibiotic resistance genes. The isolates belonged to ST48 and ST101, which have been associated with mcr and can occur in humans and fish. The mcr-1-positive E. coli persisted in 6-day biofilms, but there was a potential fitness cost. Given the status of infrastructure in Lebanon, there is a high potential for the dissemination of mcr via aquatic environments. Urgent actions are needed to control mcr and to enhance antimicrobial stewardship in Lebanon.

Antibiogram Profiles and Risk Factors for Multidrug Resistance of Salmonella enterica Recovered from Village Chickens (Gallus gallus domesticus Linnaeus) and Other Environmental Sources in the Central and Southern Peninsular Malaysia

The emergence of multidrug resistance (MDR), including colistin resistance, among Enterobacteriaceae recovered from food animals poses a serious public health threat because of the potential transmission of these resistant variants to humans along the food chain. Village chickens or Ayam Kampung are free-range birds and are preferred by a growing number of consumers who consider these chickens to be organic and more wholesome. The current study investigates the antibiogram profiles of Salmonella isolates recovered from village chicken flocks in South-central Peninsular Malaysia. A total of 34 isolates belonging to eight serotypes isolated from village chickens were screened for resistance towards antimicrobials including colistin according to the WHO and OIE recommendations of critical antibiotics. S. Weltevreden accounted for 20.6% of total isolates, followed by serovars Typhimurium and Agona (17.6%). The majority of isolates (73.5%) demonstrated resistance to one or more antimicrobials. Eight isolates (23.5%) were resistant to ≥3 antimicrobial classes. Colistin resistance (minimum inhibitory concentrations: 4-16 mg/L) was detected among five isolates (14.7%), including S. Weltevreden, S. Albany, S. Typhimurium, and Salmonella spp. Univariable analysis of risk factors likely to influence the occurrence of MDR Salmonella revealed that the flock size, poultry production system, and use of antibiotics in the farm were not significantly (p > 0.05) associated with MDR Salmonella. The current study highlights that MDR Salmonella occur at a lower level in village chickens compared to that found in live commercial chickens. However, MDR remains a problem even among free-range chickens with minimal exposure to antibiotics.

Global impact of mcr-1-positive Enterobacteriaceae bacteria on "one health"

Polymyxins, especially polymyxin B and polymyxin E (colistin), are considered to be the last line of defence against infections caused by multi-drug-resistant (MDR) gram-negative bacteria such as carbapenem-resistant Enterobacteriaceae (CRE). However, the recent emergence and dissemination of the plasmid-mediated colistin resistance gene mcr-1 and its variants pose a serious challenge to public health and the livestock industry. This review describes the prevalence and dissemination of mcr-1-positive isolates from different sources, including animals (food animals, pet animals and wildlife), humans (healthy populations and patients) and the environment (farms, urban and rural communities and natural environments) based on existing epidemiological studies of mcr-1 and MCR-1-producing Enterobacteriaceae bacteria around the world. The major mechanisms of mcr-1 transmission across humans, animals and the environment are discussed.

Research note: Occurrence of mcr-encoded colistin resistance in Escherichia coli from pigs and pig farm workers in Vietnam

WHO considers colistin as a highest priority critically important drug for human health, and occurrence of colistin-resistant bacteria in livestock is of health concern. The current study determined occurrence of colistin-resistant Escherichia coli in pigs and workers at pig farms in Vietnam, and investigated the genetic background for resistance. Colistin-resistant E. coli were detected from pigs in 53/116 (45.7%) farms, and from workers taking care of the pigs in 21/94 (22.3%) farms. Colistin-resistant isolates showed MIC to colistin between 4-16 mg/L, they were multidrug resistant (99%) and resistance was caused by the presence of mcr-1 genes in 97/102 (95.1%) E. coli from pigs and in 31/34 (91.1%) isolates from humans. mcr-1 is considered a plasmid-encoded gene, but this was not confirmed in the current investigation. In total, one pig isolate carried both mcr-1 and mcr-3 genes, whereas mcr-2, mcr-4 and mcr-5 genes were not detected. Shared resistance profiles between pig and human isolates on the same farm was only observed in four farms. The study showed that commensal E. coli from pigs in Vietnam constitute a reservoir for colistin-resitant E. coli, however, further studies are needed to confirm that mcr genes are associated with plasmids and their importance for human health.

Identification of a novel hybrid plasmid coproducing MCR-1 and MCR-3 variant from an Escherichia coli strain

OBJECTIVES

To characterize the genome of an Escherichia coli harbouring both mcr-1 and mcr-3.19 on a hybrid plasmid and the underlying transmission mechanisms.

METHODS

Broth microdilution was used to perform antimicrobial susceptibility testing. Conjugation assays and S1-PFGE were used to assess the transferability of mcr genes. Resistance genotypes and genetic contexts were investigated, based on WGS data from the Illumina and MinION platforms. Inverse PCR was performed to test the mcr-3.19-bearing circular intermediate. Bioinformatic tools were used to further characterize the hybrid plasmid.

RESULTS

E. coli CP53 was identified as harbouring both mcr-1 and mcr-3.19 on a 231 859 bp hybrid plasmid pCP53-mcr1_3 containing IncFIA, IncHI1A, IncHI1B and IncN replicons. The genetic structures of mcr-1 and mcr-3.19 were similar to those reported in other mcr-1 and mcr-3.19-bearing plasmids, which suggested that recombination between mcr-bearing plasmids had been mediated by ISs. However, the MDR plasmid pCP53-mcr1_3 cannot transfer via conjugation. Furthermore, another three plasmids were identified in the isolate, two of which encoded resistance genes. In640 duplication between two MDR plasmids was observed. An MDR-region recombination existed in E. coli CP53. A core structure consisting of mcr-3-dgkA existed in mcr-3-bearing plasmids reported, to date. Circular intermediates were observed for mcr-1 and mcr-3.19 regions.

CONCLUSIONS

A novel mcr-3.19 was identified along with mcr-1 contained in a hybrid plasmid. This finding suggested that evolution of mcr genes among various plasmids was being driven by mobile elements. Molecular surveillance of mcr gene co-occurrence warrants further investigation to evaluate the public health risk.

Audacious Hitchhikers: The Role of Travel and the International Food Trade in the Global Dissemination of Mobile Colistin-Resistance (mcr) Genes

Colistin, a last-resort antibiotic, has been used in controlling infections caused by multidrug-resistant Gram-negative bacterial pathogens. However, recent reports showed a global dissemination of mobile colistin-resistance (mcr) genes, genetic elements that encode resistance to colistin, which has raised public health concerns. These mcr genes threaten the effectiveness of colistin and could limit therapy options for complicated infections. Despite global attention, many facets of the molecular epidemiology of mcr remain poorly characterized. Here, we focus on the role of travel and the international food trade in the dissemination of mcr to countries where these genetic elements and/or colistin resistance are relatively limited in prevalence. We present evidence from the literature on the acquisition of mcr during travel, and the carriage of these genes back to travelers’ countries. We also highlight the potential transmission of mcr via imported foods. These observations emphasize the magnitude of efforts that are needed to control the spread of mcr, and further highlight the challenge of antimicrobial resistance and the urgent need for coordinated global action.

A Novel, Integron-Regulated, Class C β-Lactamase

AmpC-type β-lactamases severely impair treatment of many bacterial infections, due to their broad spectrum (they hydrolyze virtually all β-lactams, except fourth-generation cephalosporins and carbapenems) and the increasing incidence of plasmid-mediated versions. The original chromosomal AmpCs are often tightly regulated, and their expression is induced in response to exposure to β-lactams. Regulation of mobile ampC expression is in many cases less controlled, giving rise to constitutively resistant strains with increased potential for development or acquisition of additional resistances. We present here the identification of two integron-encoded ampC genes, bla_IDC-1 and bla_IDC-2 (integron-derived cephalosporinase), with less than 85% amino acid sequence identity to any previously annotated AmpC. While their resistance pattern identifies them as class C β-lactamases, their low isoelectric point (pI) values make differentiation from other β-lactamases by isoelectric focusing impossible. To the best of our knowledge, this is the first evidence of an ampC gene cassette within a class 1 integron, providing a mobile context with profound potential for transfer and spread into clinics. It also allows bacteria to adapt expression levels, and thus reduce fitness costs, e.g., by cassette-reshuffling. Analyses of public metagenomes, including sewage metagenomes, show that the discovered ampCs are primarily found in Asian countries.

Farm animals and aquaculture: significant reservoirs of mobile colistin resistance genes

Colistin resistance has attracted substantial attention after colistin was considered as a last-resort drug for the treatment of infections caused by carbapenem-resistant and/or multidrug-resistant (MDR) Gram-negative bacteria in clinical settings. However, with the discovery of highly mobile colistin resistance (mcr) genes, colistin resistance has become an increasingly urgent issue worldwide. Despite many reviews, which summarized the prevalence, mechanisms, and structures of these genes in bacteria of human and animal origin, studies on the prevalence of mobile colistin resistance genes in aquaculture and their transmission between animals and humans remain scarce. Herein, we review recent reports on the prevalence of colistin resistance genes in animals, especially wildlife and aquaculture, and their possibility of transmission to humans via the food chain. This review also gives some insights into the routine surveillance, changing policy and replacement of polymyxins by polymyxin derivatives, molecular inhibitors, and traditional Chinese medicine to tackle colistin resistance.

Complex Class 1 Integron in a Clinical Escherichia coli Strain From Vietnam Carrying Both mcr-1 and bla NDM-1

The co-production of MCR and carbapenemase in Enterobacteriaceae has been previously reported. Here, we describe a clinical strain of Escherichia coli from Vietnam carrying both mcr-1 and bla _NDM-1. Whole-genome sequencing showed that the genome of this strain consists of a 4,975,832-bp chromosome and four plasmids. The mcr-1 and bla _NDM-1 genes are located on IncI2 and IncA/C2-type plasmids, respectively. Genetic analysis revealed the presence of a multidrug-resistant region with the structure of a novel complex class 1 integron including a class 1 integron region bearing two 5' conserved segments and one 3' conserved segment and two complete structures of ISCR1. The complex integron contains aminoglycoside resistance genes aadA2, aadB, strA, strB, and aphA6, quinolone resistance gene qnrA1, extended-spectrum β-lactamase gene bla _{OXA- 4}, and a Tn125-like transposon bearing bla _NDM-1. In addition, the dfrA12-gcuF-aadA2-cmlA1-aadA1-qacH gene cassette array belonging to the sul3-type integron was also identified, but the region found downstream of the gene cassette array is the IS440-tet(M)-IS26 element instead of the sul3 gene. The results further support that Enterobacteriaceae isolates co-harboring mcr and bla _NDM are widely being distributed. The structural characteristics of the complex integron reveal that ISCR1 elements play an important role in the mobilization of bla _NDM-1 and the development of multidrug-resistant regions.

Extended-spectrum beta-lactamase-producing Escherichia coli harbouring sul and mcr-1 genes isolates from fish gut contents in the Mekong Delta, Vietnam

This study investigated the existence of sulfonamides and colistin resistance genes among extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli recovered from fish gut in Vietnam and evaluated the susceptibility patterns of the ESBL-producing E. coli to relevant antimicrobials. A total of 88 ESBL-producing E. coli isolates were analysed for the presence of the ESBLs, sul (1, 2, 3) and mcr (1-3) genes by PCR. Antimicrobial resistance phenotypes of isolates were determined by disc diffusion. Results showed that: (i) A high prevalence of 94·3% of sulfonamide resistance was observed in 88 isolates. Moreover, the existence of 2·3% of ESBL-producing E. coli harbouring mcr-1 gene were detected; (ii) The phylogenetic types A and B1 were most frequent, and the bla_CTX-M group1 and bla_TEM genes encoding ESBL were detected in 47·7% of the isolates; (iii) ESBL-producing E. coli harbouring mcr-1 gene exhibited resistance to 11 antibiotics. The existence of mcr-1 and sul1,2,3 genes and the extremely high level of multiple drug resistance in all ESBL-producing E. coli isolates obtained from sampled fish in Vietnam is a major concern. Therefore, it is imperative to monitor ESBL-producing E. coli in the river waters of Vietnam.

Occurrence and Characterization of mcr-1-Positive Escherichia coli Isolated From Food-Producing Animals in Poland, 2011-2016

The emergence of plasmid-mediated colistin resistance (mcr genes) threatens the effectiveness of polymyxins, which are last-resort drugs to treat infections by multidrug- and carbapenem-resistant Gram-negative bacteria. Based on the occurrence of colistin resistance the aims of the study were to determine possible resistance mechanisms and then characterize the mcr-positive Escherichia coli. The research used material from the Polish national and EU harmonized antimicrobial resistance (AMR) monitoring programs. A total of 5,878 commensal E. coli from fecal samples of turkeys, chickens, pigs, and cattle collected in 2011-2016 were screened by minimum inhibitory concentration (MIC) determination for the presence of resistance to colistin (R) defined as R > 2 mg/L. Strains with MIC = 2 mg/L isolated in 2014-2016 were also included. A total of 128 isolates were obtained, and most (66.3%) had colistin MIC of 2 mg/L. PCR revealed mcr-1 in 80 (62.5%) isolates recovered from 61 turkeys, 11 broilers, 2 laying hens, 1 pig, and 1 bovine. No other mcr-type genes (including mcr-2 to -5) were detected. Whole-genome sequencing (WGS) of the mcr-1-positive isolates showed high diversity in the multi-locus sequence types (MLST) of E. coli, plasmid replicons, and AMR and virulence genes. Generally mcr-1.1 was detected on the same contig as the IncX4 (76.3%) and IncHI2 (6.3%) replicons. One isolate harbored mcr-1.1 on the chromosome. Various extended-spectrum beta-lactamase (bla SHV-12, bla CTX-M-1, bla CTX-M-15, bla TEM-30, bla TEM-52, and bla TEM-135) and quinolone resistance genes (qnrS1, qnrB19, and chromosomal gyrA, parC, and parE mutations) were present in the mcr-1.1-positive E. coli. A total of 49 sequence types (ST) were identified, ST354, ST359, ST48, and ST617 predominating. One isolate, identified as ST189, belonged to atypical enteropathogenic E. coli. Our findings show that mcr-1.1 has spread widely among production animals in Poland, particularly in turkeys and appears to be transferable mainly by IncX4 and IncHI2 plasmids spread across diverse E. coli lineages. Interestingly, most of these mcr-1-positive E. coli would remain undetected using phenotypic methods with the current epidemiological cut-off value (ECOFF). The appearance and spread of mcr-1 among various animals, but notably in turkeys, might be considered a food chain, and public health hazard.

The rise and spread of mcr plasmid-mediated polymyxin resistance

Polymyxins are important lipopeptide antibiotics that serve as the last-line defense against multidrug-resistant (MDR) Gram-negative bacterial infections. Worryingly, the clinical utility of polymyxins is currently facing a serious threat with the global dissemination of mcr, plasmid-mediated polymyxin resistance. The first plasmid-mediated polymyxin resistance gene, termed as mcr-1 was identified in China in November 2015. Following its discovery, isolates carrying mcr, mainly mcr-1 and less commonly mcr-2 to -7, have been reported across Asia, Africa, Europe, North America, South America and Oceania. This review covers the epidemiological, microbiological and genomics aspects of this emerging threat to global human health. The mcr has been identified in various species of Gram-negative bacteria including Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Salmonella enterica, Cronobacter sakazakii, Kluyvera ascorbata, Shigella sonnei, Citrobacter freundii, Citrobacter braakii, Raoultella ornithinolytica, Proteus mirabilis, Aeromonas, Moraxella and Enterobacter species from animal, meat, food product, environment and human sources. More alarmingly is the detection of mcr in extended-spectrum-β-lactamases- and carbapenemases-producing bacteria. The mcr can be carried by different plasmids, demonstrating the high diversity of mcr plasmid reservoirs. Our review analyses the current knowledge on the emergence of mcr-mediated polymyxin resistance.

Colistin-resistant Escherichia coli with mcr genes in the livestock of rural small-scale farms in Ecuador

Objective

Emergence and dissemination of colistin-resistant (Co-R) bacteria harboring mobile colistin resistance genes pose a threat for treatment of infections caused by multi-drug resistant bacteria. Although the worldwide spread of Co-R bacteria is known, the precise state of Co-R bacterial dissemination in livestock of Andean countries remains unclear. Therefore, we investigated mcr-containing Co-R Escherichia coli dissemination in livestock on small-scale farms in two socioecologically different regions of Ecuador: the Amazonian rain-forest and the Pacific Coast.

Results

Sixty-six rectal swab samples from 34 pigs and 32 chickens, from five farms in the two regions, were assessed for the dissemination of Co-R E. coli using the selective medium CHROMagar™ COL-APSE. mcr-containing Co-R E. coli were detected in the specimens at a high rate (47%; 31/66), but the detection rates of the two regions were not statistically different. Both chickens and pigs showed similar detection rates. All Co-R E. coli isolates harbored mcr-1. The minimum inhibitory concentrations of colistin were ≥ 8 mg/L, and 67.7% (21/31) of the Co-R isolates were multi-drug resistant. Pulsed-field gel electrophoresis revealed the limited relation between isolates. Thus, we revealed the high rate of widespread dissemination of Co-R bacteria in livestock regardless of the socioecological conditions in Ecuador.