Evaluation of antibacterial in vitro activity of moxifloxacin and its effects on pulmonary clearance of Klebsiella pneumoniae in an animal experimental model

Moxifloxacin (CAS 186286-86-8) is a recent fluoroquinolone addressed to the treatment of respiratory infections, although clinical efficacy has been shown also in the therapy of urinary tract diseases. The in vitro activity of moxifloxacin against one encapsulated strain of Klebsiella pneumoniae was determined by means of time-kill curves and by evaluation of effects of subinhibitory concentrations on bacterial morphology by means of scanning electron microscopy. Moreover, the efficacy and time requested to eradicate the same strain from lungs was determined after intratracheal infection of guinea pigs. K. pneumoniae was rapidly killed by moxifloxacin at concentrations greater than the minimum inhibitory concentration (MIC). Subinhibitory concentrations (1/4 and 1/8 of the MIC) induced filamentation in a remarkable portion of bacteria. A progressive decrease in the bacterial content of lungs was observed during the 48-h period, with statistically significant differences compared with the control animals. In conclusion, this study provides in vivo evidence of the antimicrobial properties of moxifloxacin against K. pneumoniae.