Serotypes, virulence genes, and antimicrobial susceptibility of Escherichia coli isolates from pigs.

One hundred two pathogenic Escherichia coli isolates from diseased pigs were analyzed for serotypes, virulence genes, antimicrobial susceptibility, and the molecular basis of phenicol resistance. Of these 102 E. coli isolates, 101 were typeable and belonged to 27 different O serogroups. However, 69% of these isolates belonged to one of the following eight serogroups: O8, O54, O64, O65, O92, O108, O119, and O120. Serogroups O8 (23%) and O64 (10%) were the most prevalent among typeable isolates. High-resistance phenotypes were observed in all the isolates, with the majority displaying resistance to chloramphenicol (89%), streptomycin (83%), enrofloxacin (78%), and doxycycline (60%). The chloramphenicol resistance genes cat1, cat2, and cmlA were detected in 58%, 49%, and 65%, respectively, of the chloramphenicol-resistant isolates. The floR gene was detected in 57% of the florfenicol-resistant isolates and in 52% of chloramphenicol-resistant isolates. Pulsed-field gel electrophoresis showed that the 32 floR-positive isolates with florfenicol minimum inhibitory concentration ≥ 8 μg mL⁻¹ belonged to 25 different pulsed-field gel electrophoresis profiles, indicating the spread of floR among swine pathogenic E. coli isolates.