Ciprofloxacin induces mutagenesis to antibiotic resistance independent of UmuC in Streptococcus uberis.
Environmental Microbiology; Aug2008, Vol. 10 Issue 8, p2179-2183, 5p, 1 Diagram, 1 Chart, 1 Graph
Streptococcus uberis is an environmental bovine mastitis pathogen capable of UV-inducible SOS mutagenesis. Bacterial SOS systems can be induced by several chemicals including also antibiotics used in clinical practice. Here, we have studied the effect of ciprofloxacin, a fluoroquinolone antibiotic and known inducer of SOS, on mutations leading to antibiotic resistance in S. uberis. Mutation frequencies and spectra were compared in a wild-type S. uberis strain and its Δ umuC derivative. The results revealed that concentrations of ciprofloxacin corresponding to 0.3–0.5× minimum inhibitory concentration (MIC) induce mutagenesis independent of UmuC. Partial sequencing of the rpoB gene of individual rifampin-resistant clones from wild-type and Δ umuC strains revealed a similar but complex pattern of point mutations including transitions, transversions and deletions/insertions. It was previously shown that UV induces mainly transition-type mutations and UmuC is essential for the process. Thus, the results presented here demonstrate that S. uberis employs distinct mechanisms for ciprofloxacin and UV-induced mutagenesis, which is a striking difference to Escherichia coli SOS model. [ABSTRACT FROM AUTHOR]
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