Characterization of antimicrobial resistance genes inHaemophilus parasuisisolated from pigs in China

Abstract

BackgroundHaemophilus parasuisis a common porcine respiratory pathogen that causes high rates of morbidity and mortality in farmed swine. We performed a molecular characterization of antimicrobial resistance genes harbored byH. parasuisfrom pig farms in China.MethodsWe screened 143H. parasuisisolates for antimicrobial susceptibility against six fluoroquinolone antibiotics testing by the broth microdilution method, and the presence of 64 antimicrobial resistance genes by PCR amplification and DNA sequence analysis. We determined quinolone resistance determining region mutations of DNA gyrase (gyrAandgyrB) and topoisomerase IV (parCandparE). The genetic relatedness among the strains was analyzed by pulsed-field gel electrophoresis.ResultsSusceptibility test showed that all isolates were low resistance to lomefloxacin (28.67%), levofloxacin (20.28%), norfloxacin (22.38%), ciprofloxacin (23.78%), however, high resistance levels were found to nalidixic acid (82.52%) and enrofloxacin (55.94%). In addition, we found 14 antimicrobial resistance genes were present in these isolates, includingblaTEM-1, blaROB-1,ermB, ermA, flor, catl, tetB, tetC, rmtB, rmtD, aadA1, aac(3′)-llc, sul1, and sul2genes. Interestingly, one isolate carried five antibiotic resistance genes (tetB, tetC, flor, rmtB, sul1). The genestetB,rmtB,andflorwere the most prevalent resistance genes inH. parasuisin China. Alterations in thegyrAgene (S83F/Y, D87Y/N/H/G) were detected in 81% of the strains andparCmutations were often accompanied by agyrAmutation. Pulsed-field gel electrophoresis typing revealed 51 unique patterns in the isolates carrying high-level antibiotic resistance genes, indicating considerable genetic diversity and suggesting that the genes were spread horizontally.DiscussionThe current study demonstrated that the high antibiotic resistance ofH. parasuisin piglets is a combination of transferable antibiotic resistance genes and multiple target gene mutations. These data provide novel insights for the better understanding of the prevalence and epidemiology of antimicrobial resistance inH. parasuis.