ᰔThe main objective of this study was to determine the prevalence of the Qnr determinants in clinical and environmental Aeromonas spp. A total of 52 Aeromonas sp. isolates identified by biochemical methods (5), 25 isolated from natural waters (1) and 27 isolated from clinical samples from hospitals in Valencia, Spain, were tested for quinolone resistance by the disk diffusion method (4) (nalidixic acid, 30 g; oxolinic acid, 2 g; flumequine, 30 g; ciprofloxacin, 5 g; and levofloxacin, 5 g). Among the studied isolates, 27 showed resistance to nalidixic acid and susceptibility to ciprofloxacin, 24 isolates were susceptible to both nalidixic acid and ciprofloxacin, and only 1, the A. veronii A272 clinical isolate, was resistant to both nalidixic acid and ciprofloxacin. The isolates resistant to nalidixic acid were also resistant to oxolinic acid and flumequine. Moreover, A. veronii A272 was the only one resistant to levofloxacin. Screening of the qnrA, qnrB, and qnrS genes was performed by multiplex PCR using a set of specific primers for all isolates. Bacterial strains positive for each qnr gene were used as positive controls (Klebsiella pneumoniae UAB1 for qnrA, Escherichia coli J53 pMG252 for qnrB, and E. coli J53 pMG298 for qnrS) and were run in each batch of tested samples. Only an A. veronii clinical isolate (A. veronii A272) presented a qnr gene, which showed 100% homology with the qnrS2 gene previously reported in an isolate from the bacterial community of a wastewater treatment plant in Germany (2) and in a non-Typhi Salmonella clinical isolate in the United States (6).The qnrS2-carrying strain was identified as A. veronii by sequencing of the 16S rRNA gene (10). The MICs for nalidixic acid, ciprofloxacin, and norfloxacin were determined using the Etest method (AB Biodisk, Solna, Sweden). CLSI breakpoints were used to define susceptibility (4). The MICs showed by this strain were Ͼ256 mg/liter, 8 mg/liter, and 12 mg/liter to nalidixic acid, ciprofloxacin, and norfloxacin, respectively (Table 1). PCR amplification of the quinolone resistance-determining regions of the gyrA and parC genes was performed with primers previously described (7). A. veronii CECT 4260 and CECT 4258 strains, susceptible to quinolones, were included. The nucleotide and deduced protein sequences were analyzed with
