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Objectives: DC-159a and sitafloxacin show greater bactericidal activity against Streptococcus pneumoniae than garenoxacin and other quinolones. We investigated whether the autolysis induced by these quinolones contributes to their rapid bactericidal activity. Methods: Time-kill studies were conducted against a S. pneumoniae clinical isolate in broth with choline chloride, which is known to inhibit autolytic amidases, and lytA mutants. Western blot analysis was performed to examine LytA production. Scanning electron microscopy (SEM) was used to investigate morphological differences after exposure to quinolone. Results: Bactericidal activity of DC-159a and sitafloxacin against S. pneumoniae at 2 h of exposure to twice the minimum inhibitory concentration (MIC) was found to decrease by approximately 1 log CFU/ml when autolytic amidases were blocked. Time-kill studies using lytA mutants showed that DC-159a exhibited slower killing than that against the lytA-positive strains. On exposure to the MIC and twice the MIC of DC-159a and sitafloxacin, R6 and a clinical isolate overexpressed LytA, while garenoxacin caused a less significant increase in LytA than DC-159a and sitafloxacin. Scanning electron microscopy images revealed that R6 treated with DC-159a underwent distinct morphological changes, while the lytA mutant did not. Conclusions: The present study demonstrated that quinolone-induced autolysis may provide quinolones more powerful bactericidal activity against S. pneumoniae. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract We investigated the degree of expression of Streptococcus pneumoniae genes associated with bacteriolysis and cell death in relation to the rapid bactericidal activity of sitafloxacin. S. pneumoniae ATCC 49619 was added to brain heart infusion containing sitafloxacin and garenoxacin concentrations equivalent to the Cmax achieved with the usual single dose and 4 h post-Cmax concentration. RNA was extracted and cDNA was prepared using reverse transcriptase. Following RNA extraction and cDNA synthesis, quantitative PCR was performed to determine the amount of gene expression for 13 genes associated with cell death. Of the 13 genes analyzed, S. pneumoniae exposed for 10 min to a sitafloxacin concentration of 4 h post-Cmax showed 3.9 times increased expression of lytA compared to the control strain. Furthermore, we observed a slightly increased expression for cibA encoding a competence induced bacteriocin. Our study suggests that the induction of a lytic enzyme and bacteriocin may reflect gene expression in response to sitafloxacin accounting for part of its rapid bactericidal activity against S. pneumoniae. [ABSTRACT FROM AUTHOR]