Poultry and livestock are the most important reservoirs for pathogenic Escherichia coli and use of antimicrobials in animal farming is considered the most important factor promoting the emergence, selection and dissemination of antimicrobial-resistant microorganisms. The aim of our study was to investigate antimicrobial resistance in E. coli isolated from food animals in Jiangsu, China. The disc diffusion method was used to determine susceptibility to 18 antimicrobial agents in 862 clinical isolates collected from chickens, ducks, pigs, and cows between 2004 and 2012. Overall, 94% of the isolates showed resistance to at least one drug with 83% being resistance to at least three different classes of antimicrobials. The isolates from the different species were most commonly resistant to tetracycline, nalidixic acid, sulfamethoxazole, trimethoprim/sulfamethoxazole and ampicillin, and showed increasing resistance to amikacin, aztreonam, ceftazidime, cefotaxime, chloramphenicol, ciprofloxacin. They were least resistant to amoxicillin/clavulanic acid (3.4%) and ertapenem (0.2%). MDR was most common in isolates from ducks (44/44, 100%), followed by chickens (568/644, 88.2%), pigs (93/113, 82.3%) and cows (13/61, 21.3%). Our finding that clinical E. coli isolates from poultry and livestock are commonly resistant to multiple antibiotics should alert public health and veterinary authorities to limit and rationalize antimicrobial use in China.

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To study the prevalence and isoforms of the pathogenicity island ETT2 among pathogenic Escherichia coli, as well as to determine the relationship between the ETT2 locus and other virulence factors, PCR amplifications target to the 35 ETT2-associated genes were established and used to investigate the presence of the ETT2 locus in 168 E. coli isolates from weaned piglets with edema and/or diarrhea or dairy cows with mastitis. The results showed that the ETT2 locus could be identified in the pathogenic E. coli isolates from colibacillosis in pigs and in the ones from mastitis in cows, but the presence of ETT2 among the isolates of porcine origin were significantly higher (85.87%) than that (47.37%) of bovine origin. Furthermore, 11 ETT2 isoforms were found in this research, including an intact form and 10 deletion types. The intact ETT2 was the prevalent form among the pathogenic E. coli isolates of porcine origin, and highly associated with the presence of shigatoxin type 2e (Stx2e), while the great majority isolates of bovine origin just carried various deletion types, and no distinct association with other virulence factors, e.g., the presence/absence of LT1, ST2, Cnf2, Tra, HPI, Hly, and F17a fimbriae.

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Quinolones are broad-spectrum antibiotics that have been used for decades in treating bacterial infections in humans and animals, and subsequently bacterial resistance to these agents has increased. While studies indicated the relationship between gyrA mutations and bacterial resistance to quinolones, CRISPR/Cas9 was used in this study to investigate causal role of gyrA mutation in the quinolone resistance. In this study, 818 clinical Escherichia coli isolates were analyzed for gyrA mutations and their resistance to quinolones. The CRISPR/Cas9 system was used to generate gyrA mutations in quinolone-susceptible E. coli ATCC 25922, and quinolone-resistant clinical E. coli. The antimicrobial resistance prevalence rate in E. coli against nalidixic acid, ciprofloxacin and enrofloxacin was 77.1% (631/818), 51.1% (418/818) and 49.8% (407/818), respectively. The gyrA mutations were identified in nucleotide positions 248, 255, 259, 260, 261, 273 and 300, and mutations at positions 248 and 259 resulting in amino acid changes at positions 83 and 87 were associated with quinolone resistance. Double-site amino acid mutations increase resistance to quinolones. The gyrA mutations causing changes at amino acids 83 and 87 reversed the features of quinolone resistance in ATCC and clinical strains, verifying the causal role of gyrA mutation in the quinolone resistance of E. coli.