Antimicrobial Resistance and Virulence Profiles of mcr-1-Positive Escherichia coli Isolated from Swine Farms in Heilongjiang Province of China

Establishment and application of recombinase polymerase amplification combined with a lateral flow dipstick for the detection of mcr-1 in uncultured clinical samples

OBJECTIVES

The rapid dissemination of the mcr-1 gene via plasmid-mediated transfer has raised concerns regarding the efficacy of colistin as a last-resort treatment for multidrug-resistant Gram-negative bacterial infections. Current mcr-1 gene detection methods mainly focus on cultured bacteria, which is a complex and time-consuming process requiring skilled personnel, making it unsuitable for field analysis.

METHODS

A rapid detection technique combining recombinase polymerase amplification with a lateral flow dipstick targeting uncultured clinical samples was developed.

RESULTS

This new method targeting the mcr-1 gene region (23 232-23 642 bp, no. KP347127.1) achieved a low detection limit of 10 copies/μL. The whole process was carried out with high specificity and was completed within 20 min. The evaluation assay was conducted using 45 human faecal samples; 16 strains yielded a 98% accuracy, closely matching antimicrobial susceptibility outcomes.

CONCLUSIONS

The novel method integrates nucleic acid extraction, isothermal amplification, and a test assay, suggesting the potential for timely colistin resistance surveillance in frontline disease control and healthcare settings, supporting future prevention and clinical standardization efforts.

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.

Characterization, estimation of virulence and drug resistance of diarrheagenic escherichia coli (DEC) isolated from Tibetan pigs

In this study, we collected feces of Tibetan piglets from Nyingchi area for isolation, culture, identification, virulence gene analysis and drug resistance analysis of Escherichia Coli. The results demonstrated a 41.3% isolation rate of Diarrheagenic Escherichia Coli from Tibetan pigs with the main phylogenetic groups: group A (68.6%) and group B2 (15.7%). Typical E.coli accounted for 76.5%. The highest detection rates of porcine virulence genes were E.coli heat-resistant enterotoxin STb (58.82%) and F107 fimbrial subunit (23.53%). The highest detection rates of virulence genes from Tibetan pigs were fimC (80.39%) and ompA (76.47%). A drug sensitivity test showed that Diarrheagenic Escherichia Coli from Tibetan pigs had high drug resistance rates to mezlocillin, doxycycline and gentamicin. This study comprehensively analyzed the species composition, virulence and drug resistance of Diarrheagenic Escherichia Coli from Tibetan pigs, which provided a clearer and more targeted idea for the prevention and treatment of yellow and white dysentery in Tibetan pigs in the future.

Multiresistant Gram-Negative Pathogens—A Zoonotic Problem

BACKGROUND

Extended-spectrum-β-lactamase-producing, carbapenemase-producing, and colistin-resistant Enterobacteriaceae (ESBL-E, CPE, and Col-E) are multiresistant pathogens that are increasingly being encountered in both human and veterinary medicine. In this review, we discuss the frequency, sources, and significance of the zoonotic transmission of these pathogens between animals and human beings.

METHODS

This review is based on pertinent publications retrieved by a selective literature search. Findings for Germany are presented in the global context.

RESULTS

ESBL-E are common in Germany in both animals and human beings, with a 6-10% colonization rate in the general human population. A major source of ESBL-E is human-tohuman transmission, partly through travel. Some colonizations are of zoonotic origin (i.e., brought about by contact with animals or animal-derived food products); in the Netherlands, more than 20% of cases are thought to be of this type. CPE infections, on the other hand, are rare in Germany in both animals and human beings. Their main source in human beings is nosocomial transmission. Col-E, which bear mcr resistance genes, have been described in Germany mainly in food-producing animals and their meat. No representative data are available on Col-E in human beings in Germany; in Europe, the prevalence of colonization is less than 2%, with long-distance travel as a risk factor. The relevance of animals as a source of Col-E for human beings is not yet entirely clear.

CONCLUSION

Livestock farming and animal contact affect human colonization with the multiresistant Gram-negative pathogens CPE, ESBL-E and Col-E to differing extents. Improved prevention will require the joint efforts of human and veterinary medicine.

Characteristics of colistin-resistant Escherichia coli from pig farms in Central China

The emergence and dissemination of colistin resistance in Enterobacteriaceae mediated by plasmid-borne mcr genes in recent years now pose a threat to public health. In this study, we isolated and characterized colistin-resistant and/or mcr-positive E. coli from pig farms in Central China. Between 2018 and 2019, 594 samples were collected and recovered 445 E. coli isolates. Among them, 33 with colistin resistance phenotypes and 37 that were positive for mcr genes were identified, including 34 positive for mcr-1, one positive for mcr-3, and two positive for both mcr-1 and mcr-3. An insertion of nine bases (“CTGGATACG”) into mcr-1 in four mcr-positive isolates led to gene dysfunction, and therefore did not confer the colistin resistance phenotype. Antimicrobial susceptibility testing revealed that 37 mcr-positive isolates showed severe drug resistance profiles, as 50% of them were resistant to 20 types of antibiotics. Multilocus sequence typing revealed a heterogeneous group of sequence types in mcr-positive isolates, among which ST10 (5/37), ST156 (5/37), and ST617 (4/37) were the predominant types. Plasmid conjugation assays showed that mcr-carrying plasmids of 25 mcr-positive isolates were conjugated with E. coli recipient, with conjugation frequencies ranging from 1.7 × 10-6 to 4.1 × 10-3 per recipient. Conjugation of these mcr genes conferred a colistin resistance phenotype upon the recipient bacterium. PCR typing of plasmids harbored in the 25 transconjugants determined six types of plasmid replicons, including IncX4 (14/25), FrepB (4/25), IncI2 (3/25), IncHI2 (2/25), FIB (1/25), and IncI1 (1/25). This study contributes to the current understanding of antibiotic resistance and molecular characteristics of colistin-resistant E. coli in pig farms.

Diverse Gene Cassette Arrays Prevail in Commensal Escherichia coli From Intensive Farming Swine in Four Provinces of China

Multiple-drug resistance bacteria containing antimicrobial resistance genes (ARGs) are a concern for public health. Integrons are bacterial genetic elements that can capture, rearrange, and express mobile gene cassettes responsible for the spread of ARGs. Few studies link genotype and phenotype of swine-related ARGs in the context of mobile gene cassette arrays among commensal Escherichia coli (E. coli) in nonclinical livestock isolates from intensive farms. In the present study, a total of 264 isolates were obtained from 330 rectal swabs to determine the prevalence and characteristics of antibiotic-resistant gene being carried by commensal E. coli in the healthy swine from four intensive farms at Anhui, Hebei, Shanxi, and Shaanxi, in China. Antimicrobial resistance phenotypes of the recovered isolates were determined for 19 antimicrobials. The E. coli isolates were commonly nonsusceptible to doxycycline (75.8%), tetracycline (73.5%), sulfamethoxazole-trimethoprim (71.6%), amoxicillin (68.2%), sulfasalazine (67.1%), ampicillin (58.0%), florfenicol (56.1%), and streptomycin (53.0%), but all isolates were susceptible to imipenem (100%). Isolates [184 (69.7%)] exhibited multiple drug resistance with 11 patterns. Moreover, 197 isolates (74.6%) were detected carrying the integron-integrase gene (intI1) of class 1 integrons. A higher incidence of antimicrobial resistance was observed in the intI1-positive E. coli isolates than in the intI1-negative E. coli isolates. Furthermore, there were 17 kinds of gene cassette arrays in the 70 integrons as detected by sequencing amplicons of variable regions, with 66 isolates (94.3%) expressing their gene cassettes encoding for multiple drug resistance phenotypes for streptomycin, neomycin, gentamicin, kanamycin, amikacin, sulfamethoxazole-trimethoprim, sulfasalazine, and florfenicol. Notably, due to harboring multiple, hybrid, and recombination cassettes, complex cassette arrays were attributed to multiple drug resistance patterns than simple arrays. In conclusion, we demonstrated that the prevalence of multiple drug resistance and the incidence of class 1 integrons were 69.7 and 74.6% in commensal E. coli isolated from healthy swine, which were lower in frequency than that previously reported in China.