Characterization of three Escherichia coli clinical isolates carrying plasmid-mediated oqxAB genes.

RINCÓN GIOVANNA; PAPALIA MARIANA; ROLAN MARTÍN; GUTKIND GABRIEL; RADICE MARCELA; DI CONZA JOSÉ

Boston

Congreso; ASM Microbe 2016; 2016

American Society for Microbiology

Background: oqxAB genes encoding a multidrug efflux pump that commonly confer low resistance to quinolones and other antibiotics, but its presence may contribute to the selection of quinolone resistant mutants. oqxAB was initially detected in E. coli isolated from swine manure. However, it is infrequently reported in clinical isolates. The aim of this study was to characterize three clinical isolates of oqxAB-harboring E. coli, evaluate the inhibitory effect of phenylalanylarginine-β-naphthylamide (PAβN) and reserpine, and describe the genetic environment of this resistance marker.Methods: E. coli isolates (ER2, ER3 and DAC3) were collected in the metropolitan area in Lima, Peru. They were categorized as quinolone resistant and CTX-M-65 producers. Antimicrobial susceptibility and inhibitory effects of PAβN (50 mg/L) and reserpine (20 mg/L) were evaluated by agar dilution method according to CLSI. PMQR genes and QRDR mutations were determined by PCR and sequencing. XbaI-PFGE and MLST were used to characterize the isolates. oqxAB-containing plasmids were transferred to E. coli DH5α by electroporation. The genetic context of oqxAB was determined by PCR mapping and sequencing.Results: Isolates were resistant to nalidixic acid (NAL ≥1024 µg/ml), ciprofloxacin (32 µg/ml), levofloxacin (LVX 32 µg/ml), gatifloxacin (≥ 32 µg/ml), norfloxacin (≥128 µg/ml) and also trimethoprim- sulfamethoxazole (TMS ≥ 32/608 µg/ml) and chloramphenicol (CHL ≥128 µg/ml). In addition of oqxAB, ER3 also harbored aac(6')-Ib-cr. All of them carried two mutations in GyrA (S83L, D87N) and one in ParC (S80I). ER2 and ER3 strains were clonally related and were typified as ST602. DAC3 displayed a different banding pattern and was identified as ST448.The transfer of plasmids carrying oqxAB from ER2 and ER3 displayed an increase in TMS and CHL MICs (≥ 4 fold dilutions), however, quinolone MICs increased slightly. NAL, LVX and CHL MICs were reduced only in the presence of PAβN. The oqxA1 and oqxB3 alleles were identified in these isolates and they were always flanked downstream by IS26 and upstream by a tnpA which displayed 99% identity with IS15DI. Conclusion: E. coli harboring oqxAB displayed the same allelic variants which were surrounded by insertion sequences belonging to IS26 family. This operon has lightly modified the MICs of quinolones when it was transferred