The Action of Bacteria on Fat: Relative Merits of Various Differential Plating Mediums for Lipase Producing Organisms

Abstract

Eijkman 1 in 1901 devised a differential plating medium for lipaseproducing bacteria. According to his method, melted tallow is poured into the bottom of a culture dish and that which remains liquid is immediately poured out again, leaving a thin, solid layer covering the bottom of the dish. The inoculated melted agar medium is poured over the tallow layer. According to his description lipase-producing colonies usually cause opacity of the tallow just beneath them. Sometimes these spots are translucent, or opaque surrounded by a translucent zone. Buchanan 2 states that colonies of fat-splitting bacteria give a transparent zone in agar plates containing an emulsion of fat, and Waksman and Daviston 3 mention the use of litmus as an indicator in such plates. I have reported briefly elsewhere 4 the use of nile blue sulphate with an emulsion of oil in agar plates. In this report I shall compare and attempt to evaluate several differential plating medium for fat-splitting bacteria. They seem to fall into five groups, as shown in table 1. They vary according to composition and the mechanism by which differentiation is accomplished. The first three groups depend on changes in opacity and translucence of the fat studied for differentiation, while the last two depend on color changes due to the formation of fatty acid.