IN VITRO ACTIVITY OF TIAMULIN (81.723 HFU), A NEW PLEUROMULIN DERIVATIVE, AGAINST CLINICALLY SIGNIFICANT ANAEROBES

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The susceptibility of more than 40 strains of Gram-negative and Gram-positive anaerobes to tiamulin (Sandoz 81.723 hfu), a new pleuromulin (pleuromutilin) derivative, was determined by broth dilution and agar dilution tests. The influence of density of the inoculum upon MICs was studied by a specially designed pour plate-technique. Bacteroides fragilis, B. vulgatus, B. splanchnicus, B. oralis, B. asaccharolyticus, B. inelaninogenicus, Fusobacterium fusiforme (F. nucleatum), Sphaerophorus necrophorus, Clostridium perfringens, C. fallax, Propionibacterium aches and several species of Peptococcaceae showed broth dilution MICs of 0.03-11μg/ml. Members of B. thetaiotaomicron, B. distasonis and S. freundii (F. mortiferum) were inhibited by 8-32μg/ml and 2 strains of S. varies had a broth dilution MIC of 256μg/ml. With most strains, the agar dilution MICs were 2-4-8 times the broth dilution MICs. In pour platetests, the MICs were not considerably influenced by varying initial concentrations of viable cells. With most anaerobes, the MBCs of tiamulin were more than 100-fold higher than the MICs. The results obtained indicated that, apart from S. varies, B. thetaiotaomicron, B. distasonis and S. freundii (F. mortiferum), members of 16 other anaerobic species including B. fragilis were without exception sensitive to tiamulin.