Antimicrobial Susceptibility Patterns and Genetic Relatedness between Diarrheagenic Escherichia coli Pathotypes Isolated from Ready-to-Eat Olivier Salad and Clinical Samples.

Abstract

Diarrheagenic Escherichia coli (DEC) strains are among the most prevalent bacteria transmitted through contaminated water and food, and are related to mild-to-severe diarrhea in humans. The present study aimed to evaluate the prevalence, antibiotic resistance profile, phototypes, and biofilm formation capacity of E. coli isolates obtained from Olivier Salad and clinical samples. A total of 246 samples-including Olivier salad and stool specimens-were collected in Tehran between March to August 2022. Microbiological and molecular diagnostic methods were used to detect DEC strains. Disk diffusion and biofilm formation methods were done to evaluate the antimicrobial resistance profile and biofilm formation capacity of the E. coli isolates. Overall, 16.6% (41/246) of E. coli isolates was attained from both Olivier Salad and clinical samples and the prevalence of DEC among these isolates was 17% (7/41). The identified DEC phototypes from the 41 isolates were as follows: enteropathogenic E. coli (EPEC, 4.8%), and enterotoxigenic E. coli (ETEC, 12.1%), while, no isolates of enteroaggregative E. coli (EAEC), enterinvasive E. coli (EIEC), and enteroaggregative E. coli (EHEC) were found. The highest rate of resistance was found for amoxicillin (100%), and all DEC strains exhibited resistance to at least one antibiotic. Isolates obtained from clinical samples had more biofilm formation capacity than food samples. Our results evidenced the possibility of fecal contamination in animal-derived foods. Also, multi-drug resistances were found between DEC isolated from food that suggested animal-based foods would operate as the reservoir for multi-drug resistant bacteria. Monitoring DEC strains in both food and clinical samples is essential to improve food safety and prevent foodborne outbreaks.