Characterization of qnrB-like genes in Citrobacter species of the American Type Culture Collection

Abstract

Among five American Type Culture Collection (ATCC) Citrobacter strains, qnrB60 in Citrobacter freundii ATCC 6879, an isolate from the preantibiotic era, and qnrB61 in Citrobacter braakii ATCC 51113(T), a type strain belonging to the C. freundii complex, were identified. Meanwhile, a truncated qnrB-like pseudogene was identified in C. freundii ATCC 8090(T) and ATCC 43864. No qnrB-like sequence was found in Citrobacter koseri ATCC 27028(T). These findings underscore the close relationship between this species and qnrB.

Fig 1

Genetic map of the region between the psp and sap gene clusters of Citrobacter ATCC strains. Each underlined value is the length (bp) of the qnr-like gene/pseudogene, and its upstream/downstream environments are separated by vertical black bars. In C. koseri ATCC 27028^T, truncated putative open reading frame CKO_01383, but no qnr-like gene/pseudogene, was identified between pspF and sapA.

Fig 2

The change in qnrB61, recA, and lexA transcription due to fluoroquinolone exposure in C. braakii ATCC 51113^T. After 1 h of incubation, levofloxacin was added at a final concentration of 1× MIC (0.06 μg/ml), 0.5× MIC (0.03 μg/ml), or 0.25× MIC (0.015 μg/ml) and the bacteria were incubated for an additional 4 h. The relative expression of each gene was estimated by the ΔΔC_T method with comparison to the drug-free condition. Values are means ± standard errors of the means.