Factors in the Fermentation-Inhibition Test for Measurement of Growth-Inhibiting Antibody to Mycoplasma pneumoniae

Abstract

Factors in the fermentation-inhibition test for the measurement of growth-inhibiting antibody in serum to Mycoplasma pneumontiae were studied. The fermentation-inhibiting antibody titer, as read on the day when the color of the control cup without serum had just changed to yellow, was constant among inoculum dilutions of 10^-2 to 10^-5 (10⁶ to 10³ CFU/ml) of a M. pneumoniae broth culture. The use of 10-3 to 10-5 dilutions (10⁵ to 10³ CFU/ml) was adequate for inoculation, inasmuch as one day delay in reading did not result in a significant decrease in the test. Heat inactivation of the serum gave no significant effect on the titer. The test was simple and reliable. The growth-inhibiting antibody was shown to be detectable in the test, when the growth of M, pneumoniae was suppressed at least to 1/100 of the growth of the control without serum. The growth-inhibiting antibody titer rose later than the complement-fixing antibody titter in some cases after M. pneumoniaeinfection. It is suggested that, when an erythromycin-sensitive strain of M. pneumoniae is used, the titer transiently rises and does not show a real growth-inhibiting antibody titer in sera from patients under erythromycin administration.