Lytic effect of two fluoroquinolones, ofloxacin and pefloxacin, on Escherichia coli W7 and its consequences on peptidoglycan composition. Antimicrob. Agents Chemother

Examination of biochemical changes in Escherichia coli W7 after exposure to ofloxacin or pefloxacin revealed distinct concentration-dependent responses. At levels close to the MIC, extensive filamentation was followed by a lytic event, which involved an active protein synthesis. This lysis was correlated with changes in the peptidoglycan composition, particularly a decrease in the average glycan chain length, involving the action of the autolysines. At higher concentrations, no lysis occurred and the growth was totally inhibited as well as the protein synthesis. The peptidoglycan composition exhibited an increase in the average glycan chain length, suggesting an apparent reduced activity of the lytic transglycosylase. These results show that exposure to low concentrations of quinolones leads to the induction of lysis and peptidoglycan modifications which might contribute to the bactericidal effects of quinolones. Quinolones are broad-spectrum antibacterial agents for which the primary mechanism of action is the inhibition of DNA gyrase activity (23). The mechanism of quinolone-induced cell death has not been fully explained (3). It has been proposed that nicked DNA formed by the action of quinolone-inhibited DNA gyrase acts as a substrate fo