Quantitative measurement of the growth of pleuropneumonia-like organisms.

Accurate and reliable methods for the quantitative measurement of the growth of pleuropneumonia-like organisms have never been developed. Studies on members of this group of organisms have advanced in recent years to the stage at which further developments will be impeded by the lack of such methods. Generally techniques employed for rapid quantitation of bacterial growth, such as turbidity, packed cell volume, and dry weight, are unsuitable because of the small size and low cellular protein yields of these organisms. Estimations of the relative growth on solid media recorded as 4+, 3+, and so forth, or comparison of the relative amount of growth on a test plate with that on a control plate in which "optimal" growth occurred have been employed most frequently in the past. Holmes and Pirie (1932) attempted to relate the amount of growth with reduction time of methylene blue in the presence of lactate, and thereby construct a growth curve for the bovine pleuropneumonia organisms. Keller and Morton (1954) depicted the futility of turbidimetric measurement of whole culture in constructing growth curves for human strains. These workers successfully estimated growth by the method of least probable numbers and by calculation of the numbers of organisms from average colony counts of 100 microscopic fields. These two methods are time consuming and are not adaptable to routine use. Liebermeister (1954) assessed the suitability of media for cultivation of pleuropneumonia-like organisms by counting the number of colonies developing from 0.01 ml of liquid culture spread over the surface of an agar plate. Mean colony diameters of randomly selected colonies were employed as a measure of growth and growth inhibition by Smith and Morton (1951, 1953). Measurement of cellular nitrogen as related to optical density of resting cell suspensions have been used to standardize preparations for metabolic studies (Lecce and Morton, 1954; Rodwell and Rodwell, 1954). Although these methods are of value, none have been analyzed in regard to their accuracy and reliability. The purpose of this study was to develop and