Biological and biochemical characterization of novel lipid-like antibacterial substances (mutalipocins) produced by Streptoccus mutans strain 32K.

Two novel antibacterial substances (designated mutalipocins) have been isolated from the culture supernatant of Streptoccus mutans strain 32K (serotype c). The mutalipocins were purified by extraction of the culture supernatant with light petroleum (b.p. range 30-60 degrees C), followed by Lobar column chromatography on Lichroprep RP-8. HPLC indicated that both mutalipocin preparations (ML-I and ML-II) were homogeneous. The Mr values of ML-I and ML-II were less than 1000. Both mutalipocins were unaffected by treatment over the pH range 3.0-10.0, or with phospholipase A or proteolytic enzymes, but were partially inactivated by treatment with lipase or phospholipase C. ML-II was resistant to heat treatment. TLC indicated that ML-I and ML-II contained unsaturated, aldehyde and/or ketone, and ester groups. The inhibition of S. mutans by ML-I and ML-II was due to bactericidal, rather than bacteriostatic, activities. The antibacterial spectra of ML-I and ML-II were narrower and more species-specific than those of bacteriocins produced by other Gram-positive bacteria.