Class 1 integrons and multidrug resistance among Escherichia coli isolates from human stools

Three hundred and eighteen Escherichia coli isolates from stools of healthy volunteers and outpatients from a major university hospital in southern Thailand were tested for the presence of class 1 integrons using multiplex-PCR and for their susceptibility against 12 antimicrobial agents using standard disc diffusion method. Based on the presence of intl1, 162 isolates harbored class 1 integrons, which were more prevalent in isolates from outpatients compared with those from healthy volunteers. The majority (85%) of the isolates were resistant to at least one antimicrobial agent with the following percent resistance: streptomycin 66%, tetracycline 60%, sulphamethoxazole 59%, ampicillin 52%, trimethoprim/sulphamethoxazole 47%, kanamycin 30%, nalidixic acid 27%, ciprofloxacin 23%, norfloxacin 22%, amoxicillin/ clavulanic acid 16%, gentamicin 8%, and amikacin 2%. The most frequent pattern of multiresistant strains (11%) was sulphamethoxazole- trimethoprim/sulphamethoxazole -ampicillin-tetracycline-streptomycin. Multiple drug resistance was more frequent in integron-positive isolates (89%) than those in integron-negative E. coli (57%). These data indicate that human fecal E. coli is a reservoir of antibiotic-resistant genes that poses a significant risk of the spread of microbial resistance in the community.