Antimicrobial Resistance, Adhesin and Toxin Genes of Porcine Pathogenic Escherichia coli Following the Ban on Antibiotics as the Growth Promoters in Feed

To prevent and treat colibacillosis efficiently, a thorough understanding of the antimicrobial and virulence profiles present in porcine pathogenic Escherichia (E.) coli is needed. In this study, we isolated 196 pathogenic E. coli from the grower and finisher pigs with diarrhea for six years after the ban (July 2011) on antibiotics as the growth promoters in feed (2011-2016) in Korea. And we tested antimicrobial susceptibility and determined the prevalence of adhesin and toxin genes in these isolates. Based on the Clinical and Laboratory Standards Institute guidelines, we surveyed antimicrobial resistance of the pathogenic E. coli isolates. The most prevalent adhesin gene was F18 (43.9%), followed by AIDA-1 (37.4%). After 2013, the frequency of paa, which plays a role in attaching and effacing adhesion, decreased from 16.8 to 2.2%. The most prevalent pathotype was enterotoxigenic E. coli (49.5%), and its frequency increased from 43.0 to 57.3% after 2013. We confirmed high resistance rates to cephalothin (96.4%), ampicillin (93.9%), tetracycline (87.2%), and chloramphenicol (85.7%). After 2013, a decrease in gentamicin resistance was observed (from 52.3 to 10.1%). However, resistance to almost all other antimicrobials tested increased, especially for cefazolin (42.1 to 76.4%), cefepime (7.5 to 16.9%), cefoxitin (12.1 to 20.2%), and colistin (32.7 to 62.9%). Most isolates (98.0%) exhibited multidrug resistance. The results of this study could be used for the efficient development of control measures for enteric colibacillosis in piggeries.