Molecular Characterization of Antimicrobial Resistance in Escherichia coli from Rabbit Farms in Tai'an, China

To investigate the prevalence and resistance against antimicrobials of Escherichia coli (E. coli) in Tai'an, March 2016, a total of 55 E. coli strains were isolated from 60 faecal samples of diarrheic rabbits collected from three rabbit farms in Tai'an. The E. coli isolates were assayed for antimicrobial susceptibility and prevalence of resistance genes and Class I integrons and genotyped using Multilocus Sequence Typing (MLST). All the E. coli isolates were sensitive to ceftazidime, ceftriaxone, imipenem, and amikacin, while 78.2% of the isolates showed resistance against tetracycline, and 65.5% were resistant against ampicillin. The most common resistance gene detected was bla(TEM), present in 98.2% of isolates, followed by bla(CTX-M) (94.6%) and sul2 (58.2%). Class I integrons were detected in 17 out of the 55 (30.9%) E. coli strains. Seven kinds of gene cassette were detected: dfrA17 + aadA5, dfrA1 + catB3 + aacA4, aadA2 + LinF, dfrA1 + aadA1, aadA22, dfrA12 + orfF + addA2, and aadA16 + dfrA27 + arr-3. All the 55 E. coli strains were identified and classified as 13 sequence types (STs); ST302 (22/55, 40.0%) was the most prevalent type, followed by ST370 (12/55, 21.8%). This study showed that E. coli isolated from diarrheic farmed rabbits in the Tai'an area exhibit sometimes very frequent resistance to antimicrobials important to human medicine, which further highlights the need for reasonable use of antibiotics.