Molecular Characteristics of Fluoroquinolone-Resistant Escherichia Coli Isolated From Suckling Piglets With Colibacillosis

Objectives: Colibacillosis is a frequent enteric disease in the pig industry that causes significant economic losses. The objective of this study was to investigate the phenotypic and genotypic characteristics of fluoroquinolone (FQ)-resistant E. coli isolates from suckling piglets with colibacillosis. Results: A total of 43 FQ-resistant E. coli isolates were tested in this study and all isolates showed multi-drug resistance (MDR) and mutations in quinolone resistance determining regions ( gyrA or parC ). In particular, FQ-resistant E. coli isolates with a high FQs minimum inhibitory concentration range (≥64 mg/L for ciprofloxacin, ≥128 mg/L for enrofloxacin, and ≥256 mg/L for norfloxacin) were shown to carry double mutations in gyrA in combination with double mutations in parC . A total of 12 (27.9%) isolates were positive for the plasmid-mediated quinolone resistance (PMQR) genes, and aac(6’)-Ib-cr (7 isolates), qnrS (3 isolates), and qepA (2 isolates) were also positive. We identified the following in PMQR-positive E. coli isolates: β-lactamases–encoding blaCMY-2 (10 isolates, 83.3%), blaTEM-1 (7 isolates, 58.3%), blaOXA-1 (7 isolates, 58.3%), blaSHV-1 (3 isolates, 16.7%), and blaAAC-2 (1 isolate, 8.3%); the tetracycline resistance genes tetD (12 isolates, 100.0%), tetE (12 isolates, 100.0%), tetA (11 isolates, 91.7%), and tetB (1 isolate, 8.3%); the aminoglycoside modifying enzyme gene aac(3)-II (2 isolates, 16.7%); the sulfonamide resistance genes sul1 (9 isolates, 75.0%) and sul2 (10 isolates, 83.3%); and the chloramphenicol resistance genes (10 isolates, 83.3%). The most prevalent fimbrial antigen, combinations of toxin genes, and non-fimbrial adhesins genes were F4 (7 isolates, 58.3%), LT:STb:EAST1 (5 isolates, 41.7%), and paa (3 isolates, 25.0%), respectively. Although all PMQR-positive E. coli carried class I integrons, only 4 isolates carried the gene cassette arrangement. The most common plasmid replicon was FIB (9 isolates, 75.0%), followed by FIC, HI1, and N (7 isolates, 58.3%), respectively. Conclusions: Because FQ resistant genetic determinants that can be transferred to pathogenic bacteria in humans or pigs, critical need for comprehensive surveillance of antimicrobial resistance on pig farms.