Factors influencing growth of Mycoplasma gallisepticum in synthetic and enriched media

Abstract

The purpose of this series of exploratory investigations was two-fold: to study the effects of modifications of an enriched meat infusion medium on growth rate and colony morphology of M. gallisepticum and to develop a partially chemically defined (synthetic) medium capable of supporting growth of this strain. Media containing components of meat infusion, as well as partially defined (synthetic) media were developed which supported growth of M. gallisepticum in liquid cultures but failed to support colony formation on 1.5% agar plats. This fact indicates that the required chemical composition or physical nature of media used for culturing mycoplasma in broth cultures is not the same as required for colony formation on 1.5% Special Agar-Noble plates. When albumin or dextrin were used to adjust the surface tension of the modified media to equal that of the basal medium colony formation was successful. The test organism was successfully subcultured in broth cultures free of any serum component and also in synthetic media. The serum free medium contained casein conjugated to fatty acids and cholesterol, dialysate of PPLO broth and yeast autolysate, and glucose. It was adjusted to pH 7.6 with NaHCO₃. These investigations also support the following conclusions: (1) surface tension plays a greater role in growth of this strain on solid plates than in liquid medium; (2) the growth stimulating factor contained in PPLO serum fraction, capable of being replaced by casein, cholesterol and fatty acids, is soluble in chloroform; and (3) as the medium becomes more refined with respect to its chemical composition, 10-30% Co2 added to the atmosphere greatly enhances colony formation. Results from this research clearly showed a definite need for the development of a method for evaluating growth or presence of mycoplasma in media other than of colony formation.