Bacteriocin ST91KM, produced by Streptococcus gallolyticus subsp. macedonicus ST91KM, is a narrow-spectrum peptide active against bacteria associated with mastitis in dairy cattle.

Streptococcus gallolyticus subsp. macedonicus ST91KM produces a bacteriocin (macedocin ST91KM) active against Streptococcus agalactiae, Streptococcus dysgalactiae subsp. dysgalactiae, Streptococcus uberis, Staphylococcus aureus, and Staphylococcus epidermidis. Macedocin ST91KM is, according to tricine-SDS PAGE, between 2.0 and 2.5 kDa in size. Antimicrobial activity remained unchanged after 2 h of incubation at pH 2.0-10.0 and after 100 min at 100 degrees C. The peptide was inactivated after 20 min at 121 degrees C and when treated with proteolytic enzymes. Treatment with alpha-amylase had no effect on activity, suggesting that the mode of action does not depend on glycosylation. Amplification of the genome of strain ST91KM with primers designed from the macedocin precursor gene (mcdA) produced 2 fragments (approximately 375 and 220 bp) instead of one 150-bp fragment, as recorded for macedocin produced by Streptococcus gallolyticus subsp. macedonicus ACA-DC 198. Strain ACA-DC 198 was not available. However, DNA amplified from strain LMG 18488 (ACA-DC 206), genetically closely related to strain ACA-DC 198, revealed 99% homology to the mcdA of strain ACA-DC 198 (accession No. DQ835394). Macedocin ST91KM may thus be a second putative bacteriocin described for Streptococcus gallolyticus subsp. macedonicus.