A class IIa peptide from Enterococcus mundtii inhibits bacteria associated with otitis media

Peptide ST4SA, produced by Enterococcus mundtii ST4SA, inhibits the growth of Acinetobacter baumannii, Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, Streptococcus pneumoniae and Gram-positive bacteria isolated from patients diagnosed with middle ear infections. The peptide adsorbed at a level of 94% to S. pneumoniae 40, Pseudomonas aeruginosa 25 and E. faecium HKLHS. Low concentrations of peptide ST4SA (51 200 arbitrary units (AU)/mL) caused DNA and enzyme leakage from target cells, whilst 1 638 400 AU/mL caused cell lysis. No decrease in antimicrobial activity was observed when tested on solid medium with human blood as base. Peptide ST4SA revealed a similar level of activity compared with tetracycline (30 μg), but much higher activity compared with nasal sprays, aminoglycosides, cephalosporins, fluoroquinolones, lincosamides, macrolides, nitroimidazole, penicillin, quinolones, sulphonamides, chloramphenicol, furazolidone, fusidic acid, rifampicin, trimethoprim, trimethoprim/sulfamethoxazole and vancomycin when tested in vitro. Peptide ST4SA dissipates the proton-motive force and may be used in the treatment of multidrug-resistant strains where antibiotics are excluded from cells by efflux pumps dependent on the membrane proton gradient.