Prevalence and Characteristic of Swine-Origin mcr-1-Positive Escherichia coli in Northeastern China

Characteristics of MDR E. coli strains isolated from Pet Dogs with clinic diarrhea: A pool of antibiotic resistance genes and virulence-associated genes

The increasing number of multi-drug resistant (MDR) bacteria in companion animals poses a threat to both pet treatment and public health. To investigate the characteristics of MDR Escherichia coli (E. coli) from dogs, we detected the antimicrobial resistance (AMR) of 135 E. coli isolates from diarrheal pet dogs by disc diffusion method (K-B method), and screened antibiotic resistance genes (ARGs), virulence-associated genes (VAGs), and population structure (phylogenetic groups and MLST) by polymerase chain reaction (PCR) for 74 MDR strains, then further analyzed the association between AMRs and ARGs or VAGs. Our results showed that 135 isolates exhibited high resistance to AMP (71.11%, 96/135), TET (62.22%, 84/135), and SXT (59.26%, 80/135). Additionally, 54.81% (74/135) of the isolates were identified as MDR E. coli. In 74 MDR strains, a total of 12 ARGs in 6 categories and 14 VAGs in 4 categories were observed, of which tetA (95.95%, 71/74) and fimC (100%, 74/74) were the most prevalent. Further analysis of associations between ARGs and AMRs or VAGs in MDR strains revealed 23 significant positive associated pairs were observed between ARGs and AMRs, while only 5 associated pairs were observed between ARGs and VAGs (3 positive associated pairs and 2 negative associated pairs). Results of population structure analysis showed that B2 and D groups were the prevalent phylogroups (90.54%, 67/74), and 74 MDR strains belonged to 42 STs (6 clonal complexes and 23 singletons), of which ST10 was the dominant lineage. Our findings indicated that MDR E. coli from pet dogs carry a high diversity of ARGs and VAGs, and were mostly belong to B2/D groups and ST10. Measures should be taken to prevent the transmission of MDR E. coli between companion animals and humans, as the fecal shedding of MDR E. coli from pet dogs may pose a threat to humans.

Low prevalence of mcr-1 in Escherichia coli from food-producing animals and food products in China

BACKGROUND

mcr-1-positive Escherichia coli has emerged as a significant threat to human health, veterinary health, and food safety in recent years. After the prohibition of colistin as a feed additive in animal husbandry in China, a noticeable reduction in both colistin resistance and the prevalence of mcr-1 was observed in E. coli from animals and humans.

OBJECTIVES

To assess the prevalence of the colistin resistance gene mcr-1 and characterize its genetic context in E. coli strains derived from fecal and meat samples from food-producing animals in China.

METHODS

A total of 1,353 fecal samples and 836 food samples were collected between 2019 and 2020 in China. E. coli isolates were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and their susceptibility to colistin were determined using the broth microdilution method. The colistin-resistant E. coli isolates were screened for the presence of mcr by PCR analysis and sequencing. The minimal inhibitory concentrations (MICs) of 15 antimicrobial agents against the mcr-1-positive strains were further tested using the agar dilution method, conjugation assays were performed, and whole genome sequencing was performed using Illumina HiSeq.

RESULTS

In total, 1,403 E. coli strains were isolated. Thirteen isolates from chicken meat (n = 7), chickens (n = 3), and pigs (n = 3) were resistant to colistin with MIC values of 4 to 16 mg/L, and carried mcr-1. All mcr-1-positive strains, except for isolate AH20PE105, contained multiple resistance genes and exhibited multidrug-resistant phenotypes. They belonged to 10 sequence types (STs), including a novel ST (ST14521). mcr-1 was located on IncI2 (n = 9), IncX4 (n = 2), and IncHI2 (n = 2) plasmids, which were highly similar to other mcr-1-carrying plasmids sharing the same incompatibility type. Seven mcr-1-carrying plasmids could be successfully conjugally transferred to E. coli C600.

CONCLUSIONS

While the low prevalence of mcr-1 (0.93%) identified in this study may not immediately seem alarming, the very emergence of this gene merits attention given its implications for colistin resistance and public health. Hence, ongoing surveillance of mcr-1 in E. coli remains crucial.

Decoding the enigma: unveiling the molecular transmission of avian-associated tet(X4)-positive E. coli in Sichuan Province, China

Tigecycline is considered one of the "last resort antibiotics" for treating complex infections caused by multidrug-resistant (MDR) bacteria, especially for combating clinical resistant strains that produce carbapenemases. However, the tet(X4) gene, which carried by different plasmids can mediate high levels of bacterial resistance to tigecycline, was first reported in 2019. Here, we report the emergence of the plasmid-mediated tet(X4) in avian environment of Sichuan Province. A total of 21 tet(X4)-positive Escherichia coli (E. coli) strains were isolated and identified from avian samples in selected regions, with an isolation rate of 1.6% (21/1,286), and all of them were MDR strains. Multilocus Sequence Typing (MLST) method was used to classify the 21 tet(X4)-positive E. coli into the ST206, ST761, ST155, ST1638, ST542, and ST767 types, which also belong to the 3 phylogenetic subgroups A, B1, and C. Tet(X4) is located on mobile plasmids that can be efficiently and stably propagated. The results of fitness cost experiments showed that tet(X4)-positive plasmids may incur some fitness cost to host bacteria, but different tet(X4)-positive plasmids bring about differential fitness costs. Whole-genome sequencing further confirmed the tet(X4) gene can be located on IncX1-type plasmids and the core genetic structures are ISVsa3-rdmc-tet(X4) or rdmc-tet(X4)-ISVsa3, the former is a 7 copies tandem repeat structure. In this study, we isolated and identified tet(X4)-positive E. coli from the avian origin in Sichuan, analyzed the mobility of the tet(X4) by conjugational transfer and S1-PFGE, and evaluated the biological characteristics of the tet(X4)-positive plasmid using the results of conjugational frequency, plasmid stability, and fitness costs. Finally, combined with the third-generation whole-genome sequencing analysis, the molecular transmission characteristics of the tet(X4) were preliminarily clarified, providing a scientific basis for guiding veterinary clinical use in this area, as well as risk assessment and prevention of the transfer and spread of tigecycline resistant strains or genes.

Antimicrobial Resistance in Commensal Escherichia coli of the Porcine Gastrointestinal Tract

Antimicrobial resistance (AMR) in Escherichia coli of animal origin presents a threat to human health. Although animals are not the primary source of human infections, humans may be exposed to AMR E. coli of animal origin and their AMR genes through the food chain, direct contact with animals, and via the environment. For this reason, AMR in E. coli from food producing animals is included in most national and international AMR monitoring programmes and is the subject of a large body of research. As pig farming is one of the largest livestock sectors and the one with the highest antimicrobial use, there is considerable interest in the epidemiology of AMR in E. coli of porcine origin. This literature review presents an overview and appraisal of current knowledge of AMR in commensal E. coli of the porcine gastrointestinal tract with a focus on its evolution during the pig lifecycle and the relationship with antimicrobial use. It also presents an overview of the epidemiology of resistance to extended spectrum cephalosporins, fluoroquinolones, and colistin in pig production. The review highlights the widespread nature of AMR in the porcine commensal E. coli population, especially to the most-used classes in pig farming and discusses the complex interplay between age and antimicrobial use during the pig lifecycle.

Stability and genetic insights of the co-existence of blaCTX-M-65, blaOXA-1, and mcr-1.1 harboring conjugative IncI2 plasmid isolated from a clinical extensively-drug resistant Escherichia coli ST744 in Shanghai

Background

Co-existence of colistin, β-lactam and carbapenem in multidrug-resistant Enterobacteriaceae isolates poses a serious threat to public health. In this study, we investigated and characterized the co-occurrence of blaCTX-M-65, blaOXA-1, and mcr-1.1 strain isolated from a clinical extensively-drug-resistant Escherichia coli ST744 in Shanghai.

Methods

Antimicrobial susceptibility test was carried out by agar dilution methods. Whole genome sequencing was conducted, and resistance genes, and sequence types of colistin in E. coli isolates were analyzed. Plasmid stability and amino acid mutations were assessed in E. coli isolates.

Results

A colistin resistant E. coli ST744, named ECPX221, was identified out of 145 fecal samples collected. The strain carries a 60,168 IncI2 plasmid with the mcr-1.1 gene. The strain also has blaCTX-M-65, blaOXA-1, dfrA14, qnrS1, cmlA5, arr2, ampC, aph(4)-Ia, sul1, and aadA5 resistance genes. The plasmid pECPX221 was capable of conjugation with an efficiency of 2.6 × 10-2. Notably, 45% of the transconjugants were determined as mcr-1.1-harboring in the colistin-free environment after 60 generation of passage. No mutations occurred in pmrB, mgrB, and phoPQ gene in the mcr-1.1-harboring transconjugants. Bioinformatic analysis indicated pECPX221 shared highly similar backbone with the previously reported mcr-1.1-harboring pAH62-1, pMFDS1339.1, pSCZE4, and p2018-10-2CC. Furthermore, sequencing and phylogenetic analyses revealed a similarity between other MCR-1-homolog proteins, indicating that ECPX221 was colistin resistant.

Conclusion

The stable transferable mcr-1.1-harboring plasmid found in the E. coli ST744 strain indicated the high risk to disseminate the extensively-drug-resistance phenotype among Enterobacteriaceae.

Genomic analysis of multidrug-resistant Escherichia coli strains carrying the mcr-1 gene recovered from pigs in Lima-Peru

Antibiotic resistance is a current problem that significantly impacts overall health. The dissemination of antibiotic resistance genes (ARGs) to urban areas primarily occurs through ARG-carrying bacteria present in the gut microbiota of animals raised in intensive farming settings, such as pig production. Hence, this study aimed to isolate and analyzed 87 Escherichia coli strains from pig fecal samples obtained from intensive farms in Lima Department. The isolates were subjected to Kirby-Bauer-Disk Diffusion Test and PCR for mcr-1 gene identification. Disk-diffusion assay revealed a high level of resistance among these isolates to oxytetracycline, ampicillin, cephalothin, chloramphenicol, ciprofloxacin, and doxycycline. PCR analysis identified the mcr-1 gene in 8% (7/87) E. coli isolates. Further, whole genome sequencing was conducted on 17 isolates, including multidrug resistance (MDR) E. coli and/or mcr-1 gene carriers. This analysis unveiled a diverse array of ARGs. Alongside the mcr-1 gene, the bla_CTX-M55 gene was particularly noteworthy as it confers resistance to third generation cephalosporins, including ceftriaxone. MDR E. coli genomes exhibited other ARGs encoding resistance to fosfomycin (fosA3), quinolones (qnrB19, qnrS1, qnrE1), tetracyclines (tetA, tetB, tetD, tetM), sulfonamides (sul1, sul2, sul3), amphenicols (cmlA1, floR), lincosamides (inuE), as well as various aminoglycoside resistance genes. Additionally, Multi Locus Sequence Typing (MLST) revealed a high diversity of E. coli strains, including ST10, a pandemic clone. This information provides evidence of the dissemination of highly significant ARGs in public health. Therefore, it is imperative to implement measures aimed at mitigating and preventing the transmission of MDR bacteria carrying ARGs to urban environments.

Prevalence and Genomic Characteristics of mcr-Positive Escherichia coli Strains Isolated from Humans, Pigs, and Foods in China

Colistin is one of the last-resort antibiotics for treating infections caused by multidrug-resistant (MDR) Gram-negative bacteria. However, mcr genes conferring resistance to colistin have been widely identified, which is considered a global threat to public health. Here, we investigated the prevalence and characteristics of mcr-harboring Escherichia coli strains isolated from humans, animals, and foods in China by PCR, antimicrobial susceptibility testing, conjugation experiments, molecular typing, genome sequencing, and bioinformatics analysis. In total, 135 mcr-1-harboring E. coli isolates were acquired from 847 samples, and 6 isolates carried mcr-3. Among them, 131 isolates were MDR bacteria. Sixty-five resistance genes conferring resistance to multiple antimicrobials were identified in 135 isolates. The diverse pulsed-field gel electrophoresis (PFGE) patterns and sequence types (STs) of mcr-1-carrying isolates demonstrated that clonal dissemination was not the dominant mode of mcr-1 transmission. Seven types of plasmids were able to carry mcr-1 in this study, including IncI2, IncX4, IncHI2, p0111, IncY, and two hybrid plasmids. The genetic structures carrying mcr-1 of 60 isolates were successfully transferred into the recipient, including 25 IncI2 plasmids, 23 IncX4 plasmids, and an IncHI2 plasmid. mcr-1-pap2 was the dominant mcr-1-bearing structure, followed by ISApl1-mcr-1-pap2-ISApl1 (Tn6330) and ISApl1-mcr-1-pap2, among 7 mcr-1-bearing structures of 135 isolates. In conclusion, IncI2, IncX4, and IncHI2 plasmids were the major vectors spreading mcr-1 from different geographical locations and sources. The prevalence of Tn6330 may accelerate the transmission of mcr-1. Continuous surveillance of mcr-1 and variants in bacteria is vital for evaluating the public health risk posed by mcr genes. IMPORTANCE The spread of polymyxin-resistant Enterobacteriaceae poses a significant threat to public health and challenges the therapeutic options for treating infections on a global level. In this study, mcr-1-bearing ST10 E. coli was isolated from pigs, pork, and humans simultaneously, which demonstrated that ST10 E. coli was an important vehicle for the spread of mcr-1 among animals, foods, and humans. The high prevalence of mcr-1-positive E. coli strains in pigs and pork and the horizontal transmission of mcr-1-bearing plasmids in diverse E. coli strains suggest that pigs and pork are important sources of mcr-1-positive strains in humans and pose a potential threat to public health. Additional research on the prevalence and characteristics of mcr-1-positive E. coli is still required to facilitate early warning to improve polymyxin management in hospitals.

Co-Harboring of Beta-Lactamases and mcr-1 Genes in Escherichia coli and Klebsiella pneumoniae from Healthy Carriers and Backyard Animals in Rural Communities in Ecuador

Few studies have addressed drug resistance of Enterobacterales in rural communities in developing countries. This study aimed to determine the coexistence of extended-spectrum β-lactamase (ESBL) and carbapenemase genes in Escherichia coli and Klebsiella pneumoniae strains carrying the mcr-1 gene in rural communities in Ecuador from healthy humans and their backyard animals. Sixty-two strains, thirty E. coli and thirty-two K. pneumoniae strains carrying the mcr-1 gene were selected from a previous study. PCR were performed for the presence of ESBLs and carbapenemase genes. The strains were further characterized, and the genetic relationship was studied with multi-locus sequencing typing (MLST) of seven housekeeping genes. Fifty-nine of the sixty-two mcr-1 isolates (95%) harbored at least on β-lactam resistance gene. The most prevalent ESBL genes were the bla_TEM genes (present in in 80% of the E. coli strains) and the bla_SHV gene (present in 84% of the K. pneumoniae strains). MSLT analysis revealed 28 different sequence types (ST); 15 for E. coli and 12 for K. pneumoniae, with most ST never described in humans and animals. The coexistence of mcr-1 and β-lactams resistant genes in E. coli and K. pneumoniae strains is alarming and threatens the efficacy of last-resort antibiotics. Our findings highlight backyard animals as a reservoir of mcr-1/β-lactams resistant genes.

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.

Comparative genomic analysis of Colistin resistant Escherichia coli isolated from pigs, a human and wastewater on colistin withdrawn pig farm

In this study, genomic and plasmid characteristics of Escherichia coli were determined with the aim of deducing how mcr genes may have spread on a colistin withdrawn pig farm. Whole genome hybrid sequencing was applied to six mcr-positive E. coli (MCRPE) strains isolated from pigs, a farmworker and wastewater collected between 2017 and 2019. Among these, mcr-1.1 genes were identified on IncI2 plasmids from a pig and wastewater, and on IncX4 from the human isolate, whereas mcr-3 genes were found on plasmids IncFII and IncHI2 in two porcine strains. The MCRPE isolates exhibited genotypic and phenotypic multidrug resistance (MDR) traits as well as heavy metal and antiseptic resistance genes. The mcr-1.1-IncI2 and IncX4 plasmids carried only colistin resistance genes. Whereas, the mcr-3.5-IncHI2 plasmid presented MDR region, with several mobile genetic elements. Despite the MCRPE strains belonged to different E. coli lineages, mcr-carrying plasmids with high similarities were found in isolates from pigs and wastewater recovered in different years. This study highlighted that several factors, including the resistomic profile of the host bacteria, co-selection via adjunct antibiotic resistance genes, antiseptics, and/or disinfectants, and plasmid-host fitness adaptation may encourage the maintenance of plasmids carrying mcr genes in E. coli.

High prevalence of Escherichia coli co-harboring conjugative plasmids with colistin- and carbapenem resistance genes in a wastewater treatment plant in China

Emergence and dissemination of resistance to last-resort antibiotics such as carbapenem and colistin is a growing, global health concern. Wastewater treatment plants (WWTPs) link human activities and the environment, can act as reservoirs and sources for emerging antibiotic resistance, and likely play a large role in antibiotic resistance transmission. The aim of this study was to investigate occurrence and characteristics of colistin- and carbapenem-resistant Escherichia coli (CCREC) in wastewater and sludge samples collected over a one-year period from different functional areas of an urban WWTP in Jinan city, Shandong, China. A total of 8 CCREC were isolated from 168 samples with selective agar and PCR, corresponding to high prevalence of 4.8%, co-harboring carbapenem resistance genes (bla_NDM) and colistin resistance gene (mcr-1) and subsequently whole-genome sequenced. Additionally, all isolates were multidrug-resistant by antimicrobial susceptibility testing and carried a variety of antibiotic resistance genes. Two isolates carrying virulence genes associated with avian pathogenic E. coli were identified, one belonging to the high-risk clone O101:H9-ST167. Southern blotting was used to characterize CCREC isolates and plasmids carrying bla_NDM-genes or mcr-1 could be transferred to a recipient strain E. coli J53 by in vitro conjugation assays. Resistance to other antibiotic classes were sporadically co-transferred to the transconjugant. Transposition of and mcr-1-carrying element from a transferable IncHI2-plasmid was observed among two CCREC clones isolated within 4 days of each other. The occurrence of multidrug-resistant CCREC capable of transferring their antibiotic resistance genotypes via conjugative plasmids is alarming. WWTPs bring bacteria from different sources together, providing opportunities for horizontal exchange of DNA among compatible hosts. Further dissemination of the colistin-, carbapenem-, or both colistin- and carbapenem resistant E. coli could lead to a serious threat to public health.

Ecological risk under the dual threat of heavy metals and antibiotic resistant Escherichia coli in swine-farming wastewater in Shandong Province, China

Mineral elements and antibiotic-resistant bacterial pollutants in livestock and poultry farms' wastewater are often sources of ecological and public health problems. To understand the heavy-metal pollution status and the characteristics of drug-resistant Escherichia coli (E. coli) in swine-farm wastewater in Shandong Province and to provide guidance for the rational use of mineral-element additives, common antibiotics, and quaternary ammonium compound disinfectants on swine farms, 10 mineral elements were measured and E. coli isolated from wastewater and its resistance to 29 commonly used antibiotics and resistance genes was determined. Finally, phylogenetic and multi-locus sequence typing (MLST) analyses was performed on E. coli. The results showed serious pollution from iron and zinc, with a comprehensive pollution index of 708.94 and 3.13, respectively. It is worth noting that average iron levels in 75% (12/16) of the districts exceed allowable limits. Multidrug-resistant E. coli were found in every city of the province. The E. coli isolated from swine-farm wastewater were mainly resistant to tetracyclines (95.3%), chloramphenicol (77.8%), and sulfonamides (62.2%), while antibiotic resistance genes for quinolones, tetracyclines, sulfonamides, aminoglycosides, and β-lactams were all more than 60%. The clonal complex 10 (CC10) was prevalent, and ST10 and ST48 were dominant in E. coli isolates. Multidrug-resistant E. coli were widely distributed, with mainly A genotypes. However, the mechanism of the effect of iron on antibiotic resistance needs more study in this area. Thus, further strengthening the prevention and control of iron and zinc pollution and standardizing the use of antibiotics and mineral element additives in the swine industry are necessary.

Deep Learning and Antibiotic Resistance

Antibiotic resistance (AR) is a naturally occurring phenomenon with the capacity to render useless all known antibiotics in the fight against bacterial infections. Although bacterial resistance appeared before any human life form, this process has accelerated in the past years. Important causes of AR in modern times could be the over-prescription of antibiotics, the presence of faulty infection-prevention strategies, pollution in overcrowded areas, or the use of antibiotics in agriculture and farming, together with a decreased interest from the pharmaceutical industry in researching and testing new antibiotics. The last cause is primarily due to the high costs of developing antibiotics. The aim of the present review is to highlight the techniques that are being developed for the identification of new antibiotics to assist this lengthy process, using artificial intelligence (AI). AI can shorten the preclinical phase by rapidly generating many substances based on algorithms created by machine learning (ML) through techniques such as neural networks (NN) or deep learning (DL). Recently, a text mining system that incorporates DL algorithms was used to help and speed up the data curation process. Moreover, new and old methods are being used to identify new antibiotics, such as the combination of quantitative structure-activity relationship (QSAR) methods with ML or Raman spectroscopy and MALDI-TOF MS combined with NN, offering faster and easier interpretation of results. Thus, AI techniques are important additional tools for researchers and clinicians in the race for new methods of overcoming bacterial resistance.

Serious Risk of Tigecycline Resistance in Escherichia coli Isolated from Swine Manure

The emergence of the plasmid-mediated tigecycline resistance gene tetX family in pig farms has attracted worldwide attention. The use of tetracycline antibiotics in pig farms has a facilitating effect on the prevalence of the tetX family, but the relationship among its presence, expression, and resistance phenotype in resistant bacteria is unknown. In this study, the presence and expression characteristics of tetracycline resistance genes (TRGs) in 89 strains of doxycycline-resistant E. coli (DRE) isolated from pig manure samples from 20 pig farms under low concentrations of doxycycline stress (2 μg/mL) were analyzed. The detection rate of tetO was 96.63%, which is higher than those of other TRGs, such as tetA (94.38%), tetX (76.40%), tetB (73.03%), and tet(X4) (69.66%). At least three TRG types were present in DRE strains, which thus showed extensive resistance to tetracycline antibiotics, and 37% of these strains were resistant to tigecycline. In the presence of a low concentration of doxycycline, tetA played an important role, and the expression and existence ratio of TRGs indicated low expression of TRGs. Furthermore, the doxycycline resistance of DRE was jointly determined by the total absolute abundance of TRGs, and the absolute abundance of tetX and tet(X4) was significantly positively associated with tigecycline resistance in DRE (P < 0.05). Overall, DRE isolated from swine manure is an important reservoir of the tetX family, which suggests that DRE in swine manure has a high risk of tigecycline resistance, poses a potential threat to human health, and should be of public concern.

Characteristics of the plasmid-mediated colistin-resistance gene mcr-1 in Escherichia coli isolated from a veterinary hospital in Shanghai

The mobile colistin-resistance (mcr)-1 gene is primarily detected in Enterobacteriaceae species, such as Escherichia coli and Salmonella enterica, and represents a significant public health threat. Herein, we investigated the prevalence and characteristics of mcr-1-positive E. coli (MCRPEC) in hospitalized companion animals in a pet hospital in Shanghai, China, from May 2021 to July 2021. Seventy-nine non-duplicate samples were collected from the feces (n = 52) and wounds (n = 20) of cats and dogs and the surrounding hospital environment (n = 7). Seven MCRPEC strains, identified using screening assays and polymerase chain reaction, exhibited multidrug-resistant phenotypes in broth-microdilution and agar-dilution assays. Based in whole-genome sequencing and bioinformatics analyses, all seven isolates were determined to belong to sequence type (ST) 117. Moreover, the Incl2 plasmid was prevalent in these MCRPEC isolates, and the genetic environment of the seven E. coli strains was highly similar to that of E. coli SZ02 isolated from human blood. The isolates also harbored the β-lactamase gene bla CTX-M-65, and florfenicol resistance gene floR, among other resistance genes. Given that horizontal transfer occurred in all seven strains, E. coli plasmid transferability may accelerate the emergence of multidrug-resistant bacteria and may be transmitted from companion animals to humans. Therefore, the surveillance of MCRPEC isolates among companion animals should be strengthened.

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.

mcr-1-Mediated In Vitro Inhibition of Plasmid Transfer Is Reversed by the Intestinal Environment

Colistin is regarded as an antibiotic of last resort against multidrug-resistant Gram-negative bacteria, including Klebsiella pneumoniae and Escherichia coli. Colistin resistance is acquired by microorganisms via chromosome-mediated mutations or plasmid-mediated mobile colistin resistance (mcr) gene, in which the transfer of mcr is the predominant factor underlying the spread of colistin resistance. However, the factors that are responsible for the spread of the mcr gene are still unclear. In this study, we observed that mcr-1 inhibited the transfer of the pHNSHP45 backbone in liquid mating. Similar inhibitory effect of mcr-1.6 and chromosomal mutant ΔmgrB suggested that colistin resistance, acquired from either plasmid or chromosomal mutation, hindered the transfer of colistin resistance-related plasmid in vitro. Dual plasmid system further proved that co-existing plasmid transfer was reduced too. However, this inhibitory effect was reversed in vivo. Some factors in the gut, including bile salt and anaerobic conditions, could increase the transfer frequency of the mcr-1-containing plasmid. Our results demonstrated the potential risk for the spread of colistin resistance in the intestine, provide a scientific basis against the transmission of colistin resistance threat.

Detection of E. coli IncX1 Plasmid-Mediated mcr-5.1 Gene in an Indian Hospital Sewage Water Using Shotgun Metagenomic Sequencing: A First Report

Colistin is used against a multitude of multidrug-resistant and extremely drug-resistant Gram-negative bacterial infections. The emergence of colistin resistance is highly concerning as it may lead to the failure of this last-resort antibiotic. Since the identification of first mobile colistin resistance (mcr) genes, several variants of mcr genes have been reported, but still there are limited studies detecting mcr genes in hospital sewage water. The prevalence of mcr in the hospital environment is extremely hazardous putting health care workers, patients, and visitors at a higher risk of exposure. It may lead to a multidrug-resistant bacterial infection outbreak. In this study, we report mcr-5.1 gene in an Indian hospital sewage water using shotgun metagenomics, as a first report. The mcr-5.1 gene in the metagenome has been explored using RGI, ABRicate, NCBI database, CARD, and Resfinder. This mcr-5.1 gene harbored by Escherichia coli is a plasmid-mediated gene carried by an IncX1 plasmid pSGMCR103. The bioinformatics analysis revealed the genetic environment of mcr-5.1 gene, which consisted of mobile element protein, ChrB domain protein, putative major facilitator superfamily type transporter, and a hypothetical protein.

Large-Scale Analysis of Fitness Cost of tet(X4)-Positive Plasmids in Escherichia coli

Tigecycline is one of important antimicrobial agents for the treatment of infections caused by multidrug-resistant (MDR) Gram-negative bacteria. However, the emergence and prevalence of plasmid-mediated tigecycline resistance gene tet(X4) are threatening human and animal health. Fitness cost elicited by resistance plasmids is a key factor affecting the maintenance and transmission of antibiotic resistance genes (ARGs) in the host. A comparative analysis of the fitness cost of different types of tet(X4)-positive plasmids is helpful to understand and predict the prevalence of dominant plasmids. In this study, we performed a large-scale analysis of fitness cost of tet(X4)-positive plasmids origin from clinical isolates. These plasmids were successfully electroporated into a reference strain Escherichia coli TOP10, and a series of transformants carrying the tet(X) gene were obtained. The effects of tet(X4)-positive plasmids on the growth rate, plasmid stability, relative fitness, biofilm formation, and virulence in a Galleria mellonella model were evaluated. Consequently, we found that these plasmids resulted in varying degrees of fitness cost on TOP10, including delayed bacterial growth and attenuated virulence. Out of these plasmids, tet(X4)-harboring IncFII plasmids showed the lowest fitness cost on the host. Furthermore, by means of experimental evolution in the presence of commonly used drugs in clinic, the fitness cost of tet(X4)-positive plasmids was substantially alleviated, accompanied by increased plasmid stability. Collectively, our data reveal the differential fitness cost caused by different types of tet(X4)-positive plasmids and suggest that the wide use of tetracycline antibiotics may promote the evolution of plasmids.

Colistin Resistance and Molecular Characterization of the Genomes of mcr-1-Positive Escherichia coli Clinical Isolates

Research on resistance against polymyxins induced by the mcr-1 gene is gaining interest. In this study, using agar dilution method, polymerase chain reaction, and comparative genomic analysis, we investigated the colistin resistance mechanism of clinical E. coli isolates. The minimum inhibitory concentration (MIC) analysis results revealed that of the 515 isolates tested, bacteria with significantly increased MIC levels against colistin were isolated in 2019. Approximately one-fifth (17.14% to 19.65%) of the isolates showed MIC values ≥1 mg/L against colistin in 2015, 2016, and 2017. However, in 2019, up to three-quarters (74.11%, 146/197) of the isolates showed MIC values ≥1 mg/L against colistin indicating an increase in colistin resistance. Six isolates (EC7518, EC4968, EC3769, EC16, EC117, EC195, 1.13%, 6/515) were found to carry the mcr-1 gene and a novel mcr-1 variant with Met2Ile mutation was identified in EC3769. All six strains showed higher MIC levels (MIC=4 mg/L) than any mcr-1-negative strains (MIC ≤ 2 mg/L). Whole-genome sequencing of the six mcr-1-positive isolates revealed that EC195 carried the highest number of resistance genes (n = 28), nearly a half more than those of the following EC117 (n = 19). Thus, EC195 showed a wider resistance spectrum and higher MIC levels against the antimicrobials tested than the other five isolates. Multi-locus sequence typing demonstrated that these mcr-1-positive strains belonged to six different sequence types. The six mcr-1 genes were located in three different incompatibility group plasmids (IncI2, IncHI2 and IncX4). The genetic context of mcr-1 was related to a sequence derived from Tn6330 (ISApl1-mcr-1-pap2-ISApl1). Investigations into the colistin resistance mechanism and characterization of the molecular background of the mcr genes may help trace the development and spread of colistin resistance in clinical settings.

Molecular Epidemiology and Colistin-Resistant Mechanism of mcr-Positive and mcr-Negative Escherichia coli Isolated From Animal in Sichuan Province, China

Colistin is the last line of defense for the treatment of multidrug-resistant gram-negative bacterial infections. However, colistin resistance is gradually increasing worldwide, with resistance commonly regulated by two-component system and mcr gene. Thus, this study aimed to investigate molecular epidemiology and colistin-resistant mechanism of mcr-positive and mcr-negative Escherichia coli isolates from animal in Sichuan Province, China. In this study, a total of 101 colistin-resistant E. coli strains were isolated from 300 fecal samples in six farms in Sichuan Province. PCR was used to detect mcr gene (mcr-1 to mcr-9). The prevalence of mcr-1 in colistin-resistant E. coli was 53.47% (54/101), and the prevalence of mcr-3 in colistin-resistant E. coli was 10.89% (11/101). The colistin-resistant E. coli and mcr-1–positive E. coli showed extensive antimicrobial resistance profiles. For follow-up experiments, we used 30 mcr-negative and 30 mcr-1–positive colistin-resistant E. coli isolates and E. coli K-12 MG1655 model strain. Multi-locus sequence typing (MLST) of 30 strains carrying mcr-1 as detected by PCR identified revealed six strains (20%) of ST10 and three strains (10%) of each ST206, ST48, and ST155 and either two (for ST542 and 2539) or just one for all other types. The conjugation experiment and plasmid replicon type analysis suggest that mcr-1 was more likely to be horizontally transferred and primarily localized on IncX4-type and IncI2-type plasmid. The ST diversity of the mcr-1 indicated a scattered and non-clonal spreading in mcr-1–positive E. coli. Twenty-eight mcr-negative colistin-resistant E. coli isolates carried diverse amino acid alterations in PmrA, PmrB, PhoP, PhoQ, and MgrB, whereas no mutation was found in the remaining isolates. The finding showed the high prevalence of colistin resistance in livestock farm environments in Sichuan Province, China. Our study demonstrates that colistin resistance is related to chromosomal point mutations including the two-component systems PhoP/PhoQ, PmrA/PmrB, and their regulators MgrB. These point mutations may confer colistin resistance in mcr-negative E. coli. These findings help in gaining insight of chromosomal-encoded colistin resistance in E. coli.

Alterations in chromosomal genes nfsA, nfsB, and ribE are associated with nitrofurantoin resistance in Escherichia coli from the United Kingdom

Antimicrobial resistance in enteric or urinary Escherichia coli is a risk factor for invasive E. coli infections. Due to widespread trimethoprim resistance amongst urinary E. coli and increased bacteraemia incidence, a national recommendation to prescribe nitrofurantoin for uncomplicated urinary tract infection was made in 2014. Nitrofurantoin resistance is reported in <6% urinary E. coli isolates in the UK, however, mechanisms underpinning nitrofurantoin resistance in these isolates remain unknown. This study aimed to identify the genetic basis of nitrofurantoin resistance in urinary E. coli isolates collected from north west London and then elucidate resistance-associated genetic alterations in available UK E. coli genomes. As a result, an algorithm was developed to predict nitrofurantoin susceptibility. Deleterious mutations and gene-inactivating insertion sequences in chromosomal nitroreductase genes nfsA and/or nfsB were identified in genomes of nine confirmed nitrofurantoin-resistant urinary E. coli isolates and additional 11 E. coli isolates that were highlighted by the prediction algorithm and subsequently validated to be nitrofurantoin-resistant. Eight categories of allelic changes in nfsA, nfsB, and the associated gene ribE were detected in 12412 E. coli genomes from the UK. Evolutionary analysis of these three genes revealed homoplasic mutations and explained the previously reported order of stepwise mutations. The mobile gene complex oqxAB, which is associated with reduced nitrofurantoin susceptibility, was identified in only one of the 12412 genomes. In conclusion, mutations and insertion sequences in nfsA and nfsB were leading causes of nitrofurantoin resistance in UK E. coli. As nitrofurantoin exposure increases in human populations, the prevalence of nitrofurantoin resistance in carriage E. coli isolates and those from urinary and bloodstream infections should be monitored.