Mode of action of the lantibiotic mersacidin: inhibition of peptidoglycan biosynthesis via a novel mechanism?

Mersacidin is an antibiotic peptide produced by Bacillus sp. strain HIL Y-85,54728 that belongs to the group of lantibiotics. Its activity in vivo against methicillin-resistant Staphylococcus aureus strains compares with that of the glycopeptide antibiotic vancomycin (S. Chatterjee, D. K. Chatterjee, R. H. Jani, J. Blumbach, B. N. Ganguli, N. Klesel, M. Limbert, and G. Seibert, J. Antibiot. 45:839-845, 1992). Incubation of Staphylococcus simulans 22 with mersacidin resulted in the cessation of growth and slow lysis. Biosyntheses of DNA, RNA, and protein were not affected, whereas incorporation of glucose and D-alanine was inhibited and a regular reduction in the level of cell wall thickness was observed. Thus, unlike type A lantibiotics, mersacidin does not form pores in the cytoplasmic membrane but rather inhibits cell wall biosynthesis. Comparison with tunicamycin-treated cells indicated that peptidoglycan rather than teichoic acid metabolism is primarily affected. Mersacidin caused the excretion of a putative cell wall precursor into the culture supernatant. The formation of polymeric peptidoglycan was effectively inhibited in an in vitro assay, probably on the level of transglycosylation. In contrast to vancomycin, the activity of mersacidin was not antagonized by the tripeptide diacetyl-L-Lys-D-Ala-D-Ala, indicating that on the molecular level its mode of action differs from those of glycopeptide antibiotics. These data together with electron microscopy suggest that mersacidin acts on a novel target, which opens new perspectives for the treatment of methicillin-resistant S. aureus.