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A fermentation-inhibition test for the measurement of growth-inhibiting anti-body to acid-producing mycoplasmas was performed in microtitre plastic plates. M. pneumoniae, M. fermentans and the Negroni agent were selected for study. Antibody could be titrated since specific antiserum inhibited mycoplasma growth and the concomitant production of acid, thus preventing a change in colour of phenol red which was incorporated in the growth medium. It was essential to use unheated horse serum as a component of the growth medium. The inhibitory effect of specific antiserum was much decreased when the horse serum was heat-inacti-vated, indicating the need for a heat-labile accessory factor. The additional use of unheated guinea-pig serum was essential for demonstrating the growth-inhibiting effect of specific antiserum on the Negroni agent. The test was reproducible, specific and sensitive. Sixteen-fold or greater antibody rises were demonstrated in paired sera from volunteers infected with M. pneumoniae . Tests with ninety-five random adult sera showed that 22% had antibody to M. pneumoniae at a titre of 1/5 or more and 13–5% had antibody to M. fermentans .
Taylor‐Robinson et al. (Tue,) studied this question.