Effect of antimicrobial agents on the milky disease bacteria Bacillus popilliae and Bacillus lentimorbus.

The effects of antibiotics, sulfonamides, and other antimicrobial agents on vegetative cultures of five strains of milky disease bacteria were compared with those on Bacillus subtilis Cohn emend. Prazmowski, Staphylococcus aureus Rosenbach, Sarcina lutea Schroeter, Escherichia coli (Migula) Castellani and Chalmers, Saccharomyces pastorianus Hansen, and Mucor ramannianus Moel. Similar numbers of viable cells of each organism were exposed to the test materials by use of an antibiotic-sensitivity disc method adapted from techniques recommended by the Food and Drug Administration in the Federal Register. The results suggest that vancomycin or ristocetin, as well as a few other materials, might be useful in controlling contamination either during culture of the fastidious milky disease bacteria or in large populations of vegetative cells undergoing treatment to induce sporulation. Inhibitory concentrations of vancomycin and ristocetin in shaken-tube tests were much lower than expected in comparison with results of sensitivity-disc tests on the milky disease bacteria. Sublethal concentrations of the two antibiotics elicited some morphological change in the bacteria.