Clinical Enterobacteria with Unusual Phenotypes of Quinolone Susceptibility

30 We studied a collection of 105 clinical enterobacteria with unusual phenotypes of 31 quinolone susceptibility to analyze the occurrence of plasmid mediated quinolone resistance 32 (PMQR) and oqx genes and their implications on quinolone susceptibility. The oqxA and 33 oqxB genes were found in 31/34 (91%) Klebsiella pneumoniae and 1/3 Klebsiella oxytoca. 34 However, the oqxA/oqxB-harboring isolates lacking other known quinolone resistance 35 determinants showed wide ranges of susceptibility to nalidixic acid and ciprofloxacin. Sixty 36 of the 105 (57%) isolates harbored at least one PMQR gene (qnrB19, qnrB10, qnrB2, qnrB1, 37 qnrS1 or aac(6 ́)-Ib-cr), belong to 8 enterobacterial species, were disseminated throughout the 38 country and most of them were categorized as susceptible by the current clinical quinolone 39 susceptibility breakpoints. We developed a disk diffusion-based method to improve the 40 phenotypic detection of aac(6’)-Ib-cr. The most frequent PMQR genes in our collection 41 (qnrB19, qnrB10, aac(6’)-Ib-cr) were differentially distributed among enterobacterial species 42 and two different epidemiological settings were evident. First, the species associated to 43 community-acquired infections (Salmonella spp. and Escherichia coli) mainly harbored 44 qnrB19 (unique PMQR gene) located in small ColE1-type plasmids that might constitute its 45 natural reservoirs. qnrB19 was not associated to an extended-spectrum-β-lactamase 46 phenotype. Second, the species associated to hospital-acquired infections (Enterobacter spp., 47 Klebsiella spp. and Serratia marcescens) mainly harbored qnrB10 in ISCR1-containing class48 1 integrons that may also have aac(6’)-Ib-cr as a cassette within the variable region. These 49 two PMQR genes were strongly associated to an extended-spectrum-β-lactamase phenotype. 50 Therefore, this differential distribution of PMQR genes is strongly influenced by their linkage 51 or not to integrons. 52 53 on July 5, 2017 by gest httpaac.asm .rg/ D ow nladed fom