Prevalence and characterisation of quinolone resistance genes in Aeromonas spp. isolated from pet turtles in South Korea.

OBJECTIVES: The aim of this study was to characterise Aeromonas spp. isolated from popular species of pet turtle to assess the potential risk of pet turtles as a source of target gene alterations in the quinolone resistance-determining region (QRDR) and transferable plasmid-mediated quinolone resistance (PMQR) genes.

METHODS: Twenty-five isolates comprising four species, namely Aeromonas enteropelogenes, Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii, were obtained from healthy pet turtles. The antimicrobial susceptibility of the isolates to nalidixic acid, ciprofloxacin and ofloxacin was examined by minimum inhibitory concentration (MIC) determination. QRDR substitutions and PMQR genes were detected using conventional PCR assays and sequencing.

RESULTS: Although more than one-half of the isolates were resistant to nalidixic acid (14/25; 56%), most were susceptible to ciprofloxacin and ofloxacin. In QRDR substitution analysis, gyrA Ser-83→Ile substitution was predominant among A. enteropelogenes isolates, whilst two isolates of A. caviae displayed a novel Asp-95→Pro substitution. With regard to parC, Ser-80→Ile substitution was noted in all species except A. veronii. Furthermore, qnrS, qnrB and aac(6')-Ib-cr genes were detected in 68% (17/25), 8% (2/25) and 8% (2/25) of the isolates, respectively; 86% (12/14) of A. enteropelogenes isolates harboured a qnrS gene. Unexpectedly, quinolone resistance determinants were also detected in some isolates that were phenotypically susceptible to the tested quinolones.

CONCLUSIONS: The current study reveals the mismatch phenomenon between quinolone resistance phenotype and genotype of turtle-borne aeromonads and suggests that susceptible isolates might be a potential risk source for storage and transmission of resistance genes.