[Fundamental studies on antibacterial activity of clindamycin against Propionibacterium acnes].

Antibacterial activity of clindamycin against Propionibacterium acnes (P. acnes) was evaluated in comparison with nadifloxacin in vitro. Using a burned-infected mouse model, topical application of 1% gel form of clindamycin phosphate on P. acnes was also evaluated in in vivo. (1) The MIC of clindamycin measured by agar dilution method was 0.02 microgram/ml, and this value was smaller than that of nadifloxacin (0.3 microgram/ml). (2) At concentrations on 1-, 2- and 4- times the MIC clindamycin demonstrated bacteriostatic activity on P. acnes and showed bactericidal activity at 5-times the MIC. Nadifloxacin showed bacteriostatic activity at one half the MIC and bactericidal activity at the MIC. (3) Against acquired resistant strains of P. acnes, the highest concentrations of clindamycin and nadifloxacin that did not inhibit growth of the organism increased 5-fold higher than those against sensitive strain during 25 successive cultures in vitro. Therefore, the resistance of P. acnes was found to be emerged at almost the same ratio against both agents. (4) The chemotherapeutic effects of 1% gel form of clindamycin phosphate and 1% cream of nadifloxacin were evaluated for given subcutaneously to infected P. acnes at the burned site in mice. The topical application of either agents showed a significant reduction of number of bacteria and this result predicted clinical efficacy of topical application of clindamycin.