Objectives: To perform molecular characterization of fluoroquinolone-resistant Haemophilus parasuis isolated from South China.
Methods: H. parasuis isolates were investigated for quinolone and fluoroquinolone susceptibility and screened for plasmid-mediated quinolone resistance (PMQR) determinants by PCR amplification and DNA sequence analysis. Additionally, quinolone resistance-determining region (QRDR) mutations of DNA gyrase (gyrA and gyrB) and topoisomerase IV (parC and parE) were determined. The genetic relatedness among the strains was analysed by PFGE.
Results: These H. parasuis isolates showed higher MIC values of nalidixic acid, enrofloxacin, ciprofloxacin, levofloxacin, norfloxacin and lomefloxacin. Moreover, qnrA1, qnrB6 and aac(6')-Ib-cr were present in 2.61%, 0.87% and 2.61% of the 115 isolates, respectively. One strain possessed both aac(6')-Ib-cr and qnrA1. Mutation analysis of QRDRs showed that the resistant strains carried at least one mutation in gyrA (at codon 83 or 87), but no mutation was detected in gyrB. PFGE analysis showed great genetic diversity among these resistant H. parasuis strains.
Conclusions: The data presented here highlight the presence of qnr and aac(6')-Ib-cr genes in H. parasuis strains from South China. Moreover, the gyrA (at codon 83 or 87) mutation is linked to fluoroquinolone resistance in H. parasuis. Transferable PMQR determinants and multiple target gene mutations play important roles in the fluoroquinolone resistance of H. parasuis. These data provide important insights into the mechanism of fluoroquinolone resistance in H. parasuis, thereby highlighting the usefulness of fluoroquinolones for the treatment and control of this infection.