Antimicrobial resistance and genetic diversity of Escherichia coli isolated from humans and foods

Abstract

Antibiotic resistance has increased in recent years, raising the concern of public health authorities. We conducted a study of Escherichia coli isolates obtained from human and food samples to assess the prevalence of antimicrobial resistance and to determine the genotype and clonal relationship of 84 E. coli isolates (48 from humans and 36 from foods). An antimicrobial susceptibility test was performed using the disk diffusion method. Virulence factors were evaluated by multiplex PCR, and the clonal relationship among the resistant isolates was studied by Pulsed Field Gel Electrophoresis (PFGE). All isolates were susceptible to ceftriaxone. Overall, 26%, 20.2%, 15.4% and 6% of the isolates were resistant to tetracycline, ampicillin, sulfamethoxazole/trimethoprim and cephalotin, respectively. Twenty two percent of the isolates exhibited resistance to more than one antimicrobial agent. Multiple-drug resistance was mostly observed in the human isolates and involved the antibiotics ampicillin and tetracycline. None of the six virulence genes were identified among the isolates. Analysis of genetic diversity by PFGE of 31 resistant isolates, revealed 29 distinct restriction patterns. In conclusion, E. coli from humans and foods are resistant to commonly used antibiotics and are highly genetically diverse. In this setting, inappropriate use of antibiotics may be a cause of high resistance rate instead of clonal spread.

Figure 1. Dendrogram based on XbaI PFGE types identified among 31 E. coli strains. The data were sorted by the UPGMA method. AMP-ampicillin, TET-tetracycline, SUT- trimethoprim/sulfamethoxazole, CLO-chloramphenicol, CFL-cephalothin, AMC-amoxicillin/clavulanic acid, LVX- levofloxacin, CIP-ciprofloxacin, GEN-gentamicin, CRO-ceftriaxone, CTX-cefotaxime. *Isolates that show intermediate susceptibility to cephalotin.