Antimicrobial resistance, virulence genes, and phylogenetic background in Escherichia coli isolates from diseased pigs.

Escherichia coli isolates from diseased pigs were examined for antimicrobial susceptibility to 12 antimicrobials and possession of virulence genes (VGs), and then grouped according to the phylogenetic background and genetic relatedness. Associations between antimicrobial resistance (AMR) and VGs and between AMR and phylogenetic group were subsequently assessed. The results showed that most isolates (91%) were epidemiologically unrelated. Multiple antimicrobial-resistant phenotypes (>or=5 antimicrobials) were observed in 89% of E. coli strains and the most frequent types of resistance were to sulfamethoxazole (95%), tetracycline (94%), chloramphenicol (89%), and streptomycin (84%). The majority of isolates belonged to phylogenetic group A (84%). The most prevalent VG was EAST1 (64%), followed by Stx2e (63%) and eae (47%). Resistance to ceftiofur was associated with the presence of certain VGs, whereas resistance to doxycycline and kanamycin was associated with the absence of certain VGs. These findings suggest that multidrug resistance phenotypes, a variety of VGs, and the clear associations between resistance and VGs are commonly present in E. coli strains from diseased pigs. These results indicate that there is a great need for surveillance programs in China to monitor AMR in pathogenic E. coli strains.