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. 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.

The spread of carbapenemase-producing Enterobacterales (CPE) with colistin resistance is a critical public health issue. We genetically characterized the clinical isolate Enterobacter roggenkampii OIPH-N260, which harboured carbapenemase genes blaIMP-1 and blaGES-5 with multiple resistance genes, including mcr-9 and blaCTX-M-9. This isolate was characterized by whole-genome sequencing, comparative analysis of resistance plasmids, susceptibility tests, bacterial conjugation, S1-nuclease digested pulsed-field-gel electrophoresis, and Southern blot hybridization. The OIPH-N260 isolate exhibited resistance to most β-lactams and colistin. It co-harboured two resistance plasmids, the blaIMP-1- and blaGES-5-encoding IncP6 plasmid pN260-3 and mcr-9- and blaCTX-M-9-encoding IncHI2 plasmid pN260-1. The comparative analysis of pN260-3 indicated that a unique blaIMP-1-surrounding region was inserted into the blaGES-5-encoding plasmid with the mobile element IS26, which plays an important role in the spread of resistance genes. pN260-1 did not possess the mcr-9 expression regulative gene qseBC. Both plasmids were transferable into other bacterial species via conjugation. This is the first study to report not only a blaIMP-1 and blaGES-5 co-encoding plasmid, but also the co-harbouring of another plasmid carrying mcr-9 and blaCTX-M-9 in Enterobacter cloacae complex. The development of advanced resistance via IS26-mediated insertion and the co-harbouring of resistance plasmids highlights the need to monitor for resistance genes in CPE.

The spread of antimicrobial-resistant bacteria is a global public health problem. Carbapenem-resistant Enterobacterales are major healthcare-associated pathogens that often cause outbreaks in hospitals. ¹ Genes encoding major carbapenemases, including IMP, VIM, NDM, KPC and OXA-48, have been increasingly detected, not only in clinical settings but also in the environment. ² French imipenemases (FRIs) are a recently discovered type of carbapenemase. FRI-1–3 were reported in Europe between 2015 and 2017. ^3–5 FRI-4–7 were reported in Japan and Canada between 2017 and 2019. ^{6, 7} The increasing number of reports about FRI variants suggest that FRI carbapenemases may be spreading across the world. Enterobacter asburiae 17Nkhm-UP2 and Enterobacter sp. 18A13 were isolated from a river into which effluent is discharged from a sewage treatment plant and E. asburiae 1808-013 was isolated from the urine of a patient. Drug susceptibility testing was performed using a broth microdilution method and MICs were interpreted following the CLSI standards. ⁸ While E. asburiae 17Nkhm-UP2 and Enterobacter sp. 18A13 were resistant to both imipenem and meropenem, E. asburiae 1808-013 was resistant to imipenem and intermediate to meropenem (Table 1). Tests for carbapenemase production using the modified carbapenem inactivation method were positive, but all strains tested negative for MBL and ESBL.

Antimicrobial resistance to quinolones, which constitutes a threat to public health, has been increasing worldwide. In this study, we investigated the prevalence of quinolone-resistant determinants in Escherichia coli not susceptible to quinolones and isolated from food-producing animals and food derived from them, in the Philippines. A total of 791 E. coli strains were isolated in 56.4% of 601 beef, chicken, pork, egg, and milk samples, as well as environmental, cloacal, and rectal swab-collected samples from supermarkets, open markets, abattoirs, and poultry, swine, and buffalo farms. Using the disc diffusion method, it was determined that 78.6% and 55.4% of the isolates were resistant to at least one antimicrobial and multiple drugs, respectively. In 141 isolates not susceptible to quinolones, 115 (81.6%) harbored quinolone-resistant determinants and had mutations predominantly in the quinolone-resistance determining regions (QRDRs) of gyrA and parC. Plasmid-mediated, quinolone resistance (PMQR) and Qnr family (qnrA1, qnrB4, and qnrS1) genes were detected in all isolates. Forty-eight sequence types were identified in isolates harboring mutations in QRDR and/or PMQR genes by multilocus sequence typing analysis. Moreover, 26 isolates harboring mutations in QRDR and/or PMQR genes belonged mostly to phylogroup B1 and Enteroaggregative E. coli. In conclusion, a high prevalence of E. coli was found in food-producing animals and products derived from them, which could potentially spread high-risk clones harboring quinolone-resistance determinants.

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.

Purpose: The dissemination of colistin-resistant bacteria harboring the colistin-resistance gene mcr-1 in developing countries has recently entered the spotlight as an emerging public health threat, which is attributed to the abuse of colistin use in these countries. However, the prevalence of these bacteria in developing countries has not been extensively investigated. Therefore, in the present study, we examined the prevalence of cefotaxime-resistant commensal Escherichia coli harboring mcr-1 among residents of a representative Vietnamese village and assessed the characteristics of these isolates. Materials and methods: The stool samples, one stool sample per resident, of 612 residents were cultured on MacConkey agar with cefotaxime. Resulting E. coli-like colonies were isolated and examined further for the presence of colistin-resistant extended-spectrum β-lactamase (ESBL)-producing E. coli with mcr-1. Antibiotic susceptibility tests were performed, and clonal relationship among colistin-resistant isolates was assessed. Results: Thirty-one of the 451 cefotaxime-resistant E. coli isolates were resistant to colistin and the majority possessed mcr-1, bla_CTX-M, and/or bla_TEM, except for two isolates that produced the AmpC β-lactamase. All mcr-1 ESBL-producing E. coli isolates were multidrug-resistant (5–11 antibiotics). The isolates contained various plasmid replicon types, including the most prevalent types IncHI2 (54.8%), IncFIB (48.4%), and IncN (41.9%). In addition, 83.9% of the mcr-1 ESBL-E. coli isolates possessed a transposon ISApl1-mcr-1 segment. Furthermore, 77.4% of the mcr-1 ESBL-E. coli isolates belonged to phylogenetic group A. Pulsed-field gel electrophoresis analysis indicated limited clonal expansion of a specific strain. Conclusion: These results demonstrate the wide dissemination of colistin-resistant ESBL-E. coli harboring mcr-1 among commensal bacteria of rural residents in Vietnam, suggesting possible mobilization of the mcr-1 gene among ESBL-producing microbiota, which is a great public health concern.