Long-chain fatty acid inhibition of growth of Streptococcus agalactiae in a chemically defined medium.

Willett, Norman P. (University of Pennsylvania School of Veterinary Medicine, Kennett Square, Pa.), and Guy E. Morse. Long-chain fatty acid inhibition of growth of Streptococcus agalactiae in a chemically defined medium. J. Bacteriol. 91:2245-2250. 1966.-A chemically defined medium was developed for Streptococcus agalactiae which supported growth comparable to that obtained in complex medium. The effects of long-chain fatty acids on growth of the organisms were determined turbidimetrically. The order of activity of the fatty acids was dependent upon whether complete inhibition or median response (50% inhibition point) was used as a parameter of activity. When complete inhibition of growth was used as a measure, the degree of unsaturation of C(18) acids enhanced antimicrobial activity. However, when the median response was used as an index, this order was reversed. Increase in carbon chain from C(12) to C(18) did not correlate with either complete inhibition or median response points. Antimicrobial activity of unsaturated and saturated fatty acids was reversed by bovine serum albumin and other compounds, suggesting a bacteriostatic action.