Mycoversilin, a new antifungal antibiotic. III. Mechanism of action on a filamentous fungus Trichophyton rubrum

The antifungal activity of mupirocin

The antibacterial agent mupirocin (pseudomonic acid A) is used as a topical agent in the treatment of superficial infections by Gram-positive bacteria, particularly Staphylococcus aureus. However, we demonstrate here that the compound also inhibits the growth of a number of pathogenic fungi in vitro, including a range of dermatophytes and Pityrosporum spp. It inhibited the incorporation of amino acids and precursors of RNA, but not that of acetate, by Trichophyton mentagrophytes. It also inhibited the isoleucyl-tRNA synthetase from Candida albicans, indicating a mechanism of action similar to that in bacteria. When administered topically, mupirocin was efficacious in a T. mentagrophytes ringworm model in guinea pigs. These results suggest that mupirocin could have clinical utility for superficial infections caused by dermatophytes.

Characterization of versilin-sensitive sites in self-sensitive producer and sensitive non-producer or unrelated organism

Studies on self-sensitivity of producer mutant vs. sensitivity of non-producer parent and unrelated organism showed that versilin inhibited spore germination and sporulation in the self-sensitive producer mutant, non-producer parent Aspergillus versicolor N5 and the unrelated sensitive Trichophyton rubrum. Sporulation appeared to be more sensitive than spore germination. The inhibition of in vivo synthesis of protein was very marked, but inhibition of RNA and DNA was slight and moderate, respectively. Thus versilin was not specific in its action, but the principal sensitive site was protein synthesis, as further suggested by inhibition of polyU-directed in vitro synthesis of polyphenylalanine. The activation of leucine was unaffected, but the formation of leucyl-tRNA was severely inhibited in all three strains. The differences in sensitivities between the strains were the same, whether as whole cells or as cell-free extracts. Thus the nature of the sensitive site appeared to be identical in the self-sensitive producer and sensitive non-producer or unrelated organism.