The Inhibitory Effect of Lipase on Bacterial Growth in Media Containing Fatty Acid Esters

Abstract

Commercial bovine serum albumin (fraction V), which permits growth of small inocula of tubercle bacilli in a liquid medium containing "tween 80" (a water-soluble ester of oleic acid), also makes the medium somewhat unstable because of the presence of lipase in the albumin. The lipase effect can be eliminated by heating a neutral soln. of fraction V at 56[degree] C, by use of commercial crystalline bovine serum albumin instead of fraction V, or by addition of 0.01% NaF. It is then possible to initiate growth with smaller inocula (10-8 mg. moist wt., or 2 cells) than are effective in the presence of unheated fraction V or in the absence of albumin. Lipolytic activity also accounts for the bacteriostatic effect in this medium of horse serum and of a culture filtrate of Mycobacterium phlei. This experience emphasizes the importance of guarding against lipolytic effects when materials of biological origin are introduced into an ester-containing medium. The use of "tween 80" and tubercle bacilli provides an exceedingly sensitive bioassay for lipase.