Differential Distribution of Plasmid Mediated Quinolone Resistance Genes in Clinical Enterobacteria with Unusual Phenotypes of Quinolone Susceptibility fromArgentina

ANDRES P; LUCERO C; SOLER BISTUÉ AJ; GUERRIERO L; ALBORNOZ E; TRAN T; ZORREGUIETA A; GALAS M; CORSO, A; TOLMASKY, M E; PETRONI, A

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2013

0066-4804

We studied a collection of 105 clinical enterobacteria with unusual phenotypes of quinolone susceptibility to analyze the occurrence of plasmid mediated quinolone resistance (PMQR) and oqx genes and their implications on quinolone susceptibility. The oqxA and oqxB genes were found in 31/34 (91%) Klebsiella pneumoniae and 1/3 Klebsiella oxytoca. However, the oqxA/oqxB-harboring isolates lacking other known quinolone resistance determinants showed wide ranges of susceptibility to nalidixic acid and ciprofloxacin. Sixty of the 105 (57%) isolates harbored at least one PMQR gene (qnrB19, qnrB10, qnrB2, qnrB1, qnrS1 or aac(6´)-Ib-cr), belong to 8 enterobacterial species, were disseminated throughout the country and most of them were categorized as susceptible by the current clinical quinolone susceptibility breakpoints. We developed a disk diffusion-based method to improve the phenotypic detection of aac(6´)-Ib-cr. The most frequent PMQR genes in our collection (qnrB19, qnrB10, aac(6´)-Ib-cr) were differentially distributed among enterobacterial species and two different epidemiological settings were evident. First, the species associated to community-acquired infections (Salmonella spp. and Escherichia coli) mainly harbored qnrB19 (unique PMQR gene) located in small ColE1-type plasmids that might constitute its natural reservoirs. qnrB19 was not associated to an extended-spectrum-β-lactamase phenotype. Second, the species associated to hospital-acquired infections (Enterobacter spp., Klebsiella spp. and Serratia marcescens) mainly harbored qnrB10 in ISCR1-containing class-1 integrons that may also have aac(6´)-Ib-cr as a cassette within the variable region. These two PMQR genes were strongly associated to an extended-spectrum-β-lactamase phenotype. Therefore, this differential distribution of PMQR genes is strongly influenced by their linkage or not to integrons.