Antimicrobial Resistance, Resistance Genes and Virulence Genes in Salmonella Isolates From Chicken

Ninety eight Salmonella isolates (53 isolates from 2007 and 45 from 2009) from diseased chicken were examined for antimicrobial susceptibility to 15 antimicrobials, possession of resistance and virulence genes and Pulsed Field Gel Electrophoresis (PFGE) patterns. The 82 (84%), all 45 from 2009 and 37 from 2007 were resistant to 2 or more antimicrobials. A single isolate from 2009 was resistant to 13 of the 15 antimicrobials tested. The isolates from 2009 exhibited significantly greater resistance to streptomycin, florfenicol, tetracycline, doxycycline and nalidixic acid than that from 2007. Resistance genes sul3 and aadA1 were the most prevalent being found in 19 (36%) and 14 (31%) isolates from 2007 and 2009, respectively. All 98 isolates carried invA; in comparison with the isolates from 2007, the isolates from 2009 exhibited significantly lower rates of carrying spvC, sopE and iroB. Of the 98 isolates, 75 isolates were successfully typed, resulting in 49 different PFGE patterns with a difference of at least seven bands. This study shows that the majority of Salmonella strains from Guangdong display resistance to multiple antimicrobial compounds and carry multiple resistance genes and virulence genes.