The spectrum of antimicrobial activity of the bacteriocin subtilosin A

Bacterocins are antimicrobial peptides produced by bacteria with a relatively narrow range of activity against closely related organisms. Subtilosin A is a bacteriocin produced by Bacillus subtilis that has activity against Listeria monocytogenes, which might indicate antimicrobial activity unusual for bacteriocins.

To examine the antimicrobial activity and factors affecting the activity of subtilosin A against a range of potentially pathogenic bacteria.

The peptide was purified from cultures of B. subtilis and the MIC determined for 18 species of bacteria using a microdilution methodology. The extent of capsule formation was determined using microscopic examination of cells mounted in India ink. Protease mutants of a susceptible bacteria and mild heat shock were used to examine the effect of environmental stress on subtilosin A activity.

Subtilosin A proved to have antimicrobial activity against a wide range of bacteria including Gram-positive and Gram-negative bacteria and both aerobes and anaerobes. The peptide was less effective against capsulated forms of two Gram-negative bacteria than the non-capsulated strains of either. Heat shock but not protease activity also altered the effectiveness of the bacteriocin.

Subtilosin A has limited antimicrobial activity against a number of human pathogens which, combined with its relative ineffectiveness against some capsulated pathogens, may limit its usefulness as a human therapeutic.