Objective. Determine the frequency of diarrheagenic Escherichia coli pathotypes colonizing swine. Materials and Methods. E. coli strains isolated of fecal samples from 280 swine, produced for local consumption, in a semi-technical farm of Morelos state, (central Mexico) were tested to identify the diarrheagenic E. coli pathotypes by multiplex PCR. Results. Of the 521-diarrheagenic E. coli isolates examined, 50 (9.6%) were positive for at least one virulence gene in 42 different animals. Thus, 15% (42/280) of the swine in this farm were colonized with pathogenic E. coli. Among the E. coli isolates, the pathotype EPEC (6.5%) was the most frequently, followed by EHEC (2.3%), ETEC and EIEC (0.4%). Conclusions. In this study, four different E. coli pathotypes were found among swine colonized by E. coli in this farm. Thus, these swine are reservoirs for these virulent bacteria and there is potential risk of causing diarrhea in swine and in the population consuming the meat.

The use of colistin in food-producing animals favors the emergence and spread of colistin-resistant strains. Here, we investigated the occurrence and molecular mechanisms of colistin resistance among E. coli isolates from a Mexican piglet farm. A collection of 175 cephalosporin-resistant colonies from swine fecal samples were recovered. The colistin resistance phenotype was identified by rapid polymyxin test and the mcr-type genes were screened by PCR. We assessed the colistin-resistant strains by antimicrobial susceptibility test, pulse-field gel electrophoresis, plasmid profile, and mating experiments. Whole-Genome Sequencing data was used to explore the resistome, virulome, and mobilome of colistin-resistant strains. A total of four colistin-resistant E. coli were identified from the cefotaxime-resistant colonies. All harbored the plasmid-borne mcr-1 gene, which was located on conjugative 170-kb IncHI-2 plasmid co-carrying ESBLs genes. Thus, high antimicrobial resistance rates were observed for several antibiotic families. In the RC2-007 strain, the mcr-1 gene was located as part of a prophage carried on non-conjugative 100-kb-plasmid, which upon being transformed into K. variicola strain increased the polymyxin resistance 2-fold. The genomic analysis showed a broad resistome and virulome. Our findings suggest that colistin resistance followed independent acquisition pathways as clonal and non-genetically related mcr-1-harboring strains were identified. These E. coli isolates represent a reservoir of antibiotic resistance and virulence genes in animals for human consumption which could be potentially propagated into other interfaces.

The accelerated spread of antimicrobial resistance, driven by the misuse of antibiotics in the context of ‘One Health’, is a public health concern worldwide due to the increasing number of human infections associated with foodborne and/or environmental pathogens, including multidrug-resistant Escherichia coli (E. coli). Monitoring pathogenic and multidrug-resistant E. coli isolates is essential for sustainable disease management in swine and human diarrhea cases. This study was designed to assess the multidrug resistance (MDR) profiles and virulence-associated gene (pathotypes) frequency of pathogenic and commensal E. coli strains by antimicrobial susceptibility testing and endpoint PCR among 983 E. coli isolates from swine fecal material and 425 stool isolates from human diarrhea cases, obtained from a closely monitored population between March 2015 and April 2016. Our results reveal that >50% of E. coli strains isolated from swine were resistant to nalidixic acid (78.94%), tetracycline (72%), ampicillin (55.54%), and co-trimoxazole (53.91%), and that, in humans, the highest resistance was observed in tetracycline (71.77%), nalidixic acid (65.41%), ampicillin (57.88%), and co-trimoxazole (53.88%). A lower frequency of resistance to ciprofloxacin was demonstrated in both swine (23.4%) and humans (15.3%), and minimal resistance to third-generation cephalosporins, ceftazidime (2.54%), and cefotaxime (2.44%) was observed in swine; however, resistance to these cephalosporins is much higher at 14.6% and 11.53% in humans. Among the pathotypes, EPEC was the most predominant (70.97%) in swine and DAEC (40%) in humans. In addition, pulsed-field gel electrophoresis separates the E. coli isolates into 22 patterns. Pathotypes such as EPEC and EHEC in swine highlight the need for surveillance and control in animal production to prevent zoonotic transmission. These results suggest that swine could act as a reservoir in human infection and that antimicrobial resistance could be transferred to humans from swine. Although we did not find clonal dissemination between the human and swine strains, the spread of similar multi-resistance profiles was observed, thus suggesting that multidrug resistance has been widely selected in this closed environment and may pose a public health risk.