The interrelationship of bacterial lipid composition and the antimicrobial activity of the antioxidant butylated hydroxyanisole

Two species of Pseudomonas were grown in the presence of sublethal concentrations of the phenolic antimicrobial antioxidant butylated hydroxyanisole (BHA). The effect that BHA had in the growth media on the bacterial fatty acid and phospholipid composition and the relation-ship of any modifications of the composition to the susceptibility of the microorganism was determined. Microbial lipids were extracted and analyzed by gas chromatography. Phospholipids were assayed using thin layer chromatography. Pseudomonas fluorescens was almost totally inhibited by the presence of 150 ppm BHA for 15 minutes. The relative percentage of unsaturated fatty acids in the total lipid fraction was 58.14%. Growth in the presence of 50-125 ppm BHA caused a decrease in the relative ratio of unsaturated to saturated fatty acids for both total and polar lipid fractions while resistance to the antimicrobial effects of BHA increased. Decreased susceptibility also paralleled a decrease in phosphatidyl ethanolamine content and an increase in phosphatidyl glycerol and phosphatidyl inositol contents. Modified lipid content and decreased susceptibility were maintained through one transfer in broth without BHA. Control cells of Pseudomonas fragi were relatively resistant to the effect of BHA. The relative percentage of unsaturated fatty acids in the total lipid fraction was 37.57% for the control population and treated cells maintained approxi-mately 38% unsaturated fatty acids as well. Changes in the polar fatty acid and phospholipid composition of P. fragi paralleled alterations in the bacterial susceptibility to BHA. When the lethal effects of BHA against a variety of both gram-positive and gram-negative organisms were determined in relation to the total and polar fatty acid composition of the cytoplasmic membrane, a definitive relationship between total and polar fatty acid composition and sus-ceptibility of a bacterial species to BHA could not be elucidated. Increased levels of saturated fatty acids did not confer protection and cell gram reaction did not appear to be a strict indicator of bacterial susceptibility to BHA. The antimicrobial activity of BHA, while associated with changes in lipid composition, may be more directly mediated through alteration of the activity of membrane bound enzyme systems.