SUMMARY: Under standard conditions of subculturing in increasing drug concentrations, licheniformin and subtilin (polypeptide-containing antibiotics from the genus ) induced resistance in more slowly and to a much smaller degree than did streptomycin. Strains resistant to licheniformin and subtilin tended to revert, whereas streptomycin-resistance was stable. Licheniformin resistance was somewhat more difficult to induce and less stable than subtilin resistance.

Cross-resistance tests of bacteriostatic activity between the resistant strains and the three antibiotics distinguished completely licheniformin from both subtilin and streptomycin. Although the difference between licheniformin and subtilin was largely confirmed by a more sensitive bactericidal test, making viable counts after varying periods of exposure of the resistant strains to the antibioties in nutrient medium, the test, nevertheless, revealed a minor overlap between the two antibiotics, which was either the result of contamination of one by the other or, more probably, the expression of some common chemical property. Licheniformin and subtilin differed in the speed of their lethal action on , subtilin being much the slower.

When was exposed to mixtures of streptomycin and licheniformin in certain proportions, the rapid development of high streptomycin resistance, was prevented.


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