Biomedical subjects
Publications and source records attributed to M Matsukawa.
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The in vitro bactericidal effects of therapeutic concentrations of levofloxacin (LVFX) on clinical isolates of Pseudomonas aeruginosa and Enterococcus faecalis were assessed. Starting from 10(7) CFU/ml, the bacterial count was determined serially during the exposure to LVFX present at concentrations automatically simulated to its clinically achievable urinary levels at the recommended dosage (100 mg 3 times daily). An isolate of P. aeruginosa for which the MIC of LVFX was 16 microgram/ml was completely eradicated after 10 h of exposure to LVFX. On the other hand, 40 h of exposure to LVFX were required for complete eradication of an isolate of E. faecalis with equal susceptibility, although the bacterial count was rapidly reduced to 10(2) CFU/ml in the early phase of the exposure. It was concluded that LVFX exerts a more potent bactericidal effect on P. aeruginosa than on E. faecalis despite a similar susceptibility of these organisms to LVFX.
To study the changes of bacterial susceptibility during exposure to antimicrobials, the respective minimal inhibitory concentrations (MICs) of 50 colonies from each of various bacterial test strains were determined in an experimental system using an in vitro urinary bladder model. The MICs of gatifloxacin and meropenem for Pseudomonas aeruginosa strains were not homogeneous before exposure to the drugs. The MICs of the strains examined reflected only that of their dominant population. When starting from 10(7)CFU/ml, the bacterial count was determined serially during exposure to gatifloxacin or meropenem in therapeutic urinary concentrations. The MIC of the less susceptible population of each strain was changed serially to a higher one. The more susceptible strains were eradicated before the change of the MIC. The bacteria originally consisted of strains having heterogeneous susceptibility to drugs, in which major strains had susceptibility expressed by the MIC and minor ones had a higher or lower MIC. This heterogeneity may be responsible for the change of susceptibility in strains after exposure to the drugs.