Thiolactomycin, a new antibiotic. III. In vitro antibacterial activity.

Thiolactomycin is a new broad-spectrum antibiotic, active in vitro against many species of Gram-positive cocci, Enterobacteriaceae, Haemophilus, acid-fast bacteria and anaerobic bacteria. However, the activity is generally moderate and bacteriostatic in action. This antibiotic eludes cross resistance with any of the known antibacterial drugs such as ampicillin, carbenicillin or cycloserine. The effect on Gram-negative bacilli in vitro is little affected by the inoculum size, the presence of horse serum, the pH of the medium or the type of medium. When thiolactomycin was added to the assay medium, the minimum inhibitory concentration of ampicillin against inducible beta-lactamase producing strains of Staphylococcus aureus and Pseudomonas aeruginosa was reduced. Thiolactomycin inhibited the production of inducible beta-lactamase in several organisms.