Modifications of the Growth Inhibition Test and its Application to Human T-Mycoplasmas

Abstract

Several factors were found to influence the growth inhibition test. Inoculum size and amount of antiserum are well known variables, but the method of applying the antiserum, the incubation temperature, and the pH of the agar medium also play significant roles. The growth inhibition test modified according to these findings was found to be specific and well suited for the classification and identification of human T-mycoplasmas.

A Modification of the Mycoplasma Serum‐Drop Growth Inhibition Test

“…This contrasts with results with other types of the GI test, e.g. those of Black (1973) who found that reducing the growth temperature from 37" to 25 OC resulted in a two-fold increase in the inhibition zone diameters with ureaplasmas, an effect attributed to the slower growth rate allowing longer time for effective diffusion of antisera. With the present modified serum-drop test, the immediate superficial spread of antiserum applied to the agar surface probably ensures that lateral diffusion through the agar is not a significant factor ,affecting growth inhibition.…”

“…The possibility of preparing large stocks of antiserum containing discs that can be stored for several years makes the method simple and time-saving to perform. It has some disadvantages, however: it is rather insensitive (Black 1973); the borderline between growth and absence of growth is not always clear-cut; a partial inhibition may be produced by less potent antisera and occasional occurrence of 'break-through' colonies may interfere with reading of the test.…”

“…This was done as described by Black (1973) using agar-wells 4 mm in diameter containing 0.025 m l l of antiserum.…”

“…Edward reported that antiserum incorporated in the growth medium inhibited the growth of the homologous mycoplasma species. Since then several modifications of the method have been described (Herderschee 1963: Jensen 1963Clyde 1964: Stanbridge & Hayflick 1967: Ogra & Bohl 1970Campello et al 1972;Black 1973).…”

“…The growth inhibition (GI) test is used extensively for identification and classification of mycoplasmas because of its simplicity of performance and high degree of specificity. On the other hand, the test is generally recognized to be rather insensitive, although less so when using the agar-well mlzthod (Black 1973) rather than the disc technique originally devised by Clyde (1964). In general, however, the GI test is not suitable for measurement of antibodies resulting from mycoplasma infection in humans and animals, as opposed to those produced by hyper-immunization.…”