Abstract
Factors in the fermentation inhibition test for the measurement of growth inhibiting antibody of serum to M. pneumoniae were examined and the following results were obtained:
1) Serial ten-fold dilutions of the broth culture of M. pneumoniae were inoculated into cups of a microtiter plate and the color change of the medium to yellow with the growth of M. pneumoniae was observed. The cup inoculated with the 10-1 dilution (about 107 CFU/ml) changed the color to yellow after 3 days' incubation, then the color change proceeded with the increase of dilutions, and the cup inoculated with the 10-6 dilution (about 102 CFU/ml) changed the color on the 14th day, disclosing that the cup inoculated with 1 to 10 CFU changed the color on the 14th day.
2) When the reading in the fermentation inhibition test was made on the day when the color of the control cup without serum changed to yellow, the growth inhibiting antibody titer was shown to be constant among the inoculations of 10-2 to 10-5 dilutions (about 106 to 103 CFU/ml) of the broth culture. Thus it was concluded that the use of 10-3 to 10-5 dilutions (105 to 103 CFU/ml) was adequate for the inoculation in the fermentation inhibition test, because the one day delay in reading in the 10-2 dilution resulted in a significant decrease in the titer.
3) Heat inactivation of the serum at 56°C for 30 minutes had no significant effect on the growth inhibition titer. Heated sera tended to show more constant titers among varied dilutions of the broth culture.
4) The growth inhibiting antibody was shown to be detectable in this test, when the growth of M. pneumoniae was suppressed to 1/100 or less as compared with the control without serum.
5) The growth inhibiting antibody titer was determined in sera from children who had not been given any antibiotics. Sera with complement fixing antibodytiter of<1:4 to M. pneumoniae showed the growdth inhibiting antibody titer of<1:4, and the course of the growth inhibiting antibody titer of serial sera obtained from 7 patients with M. pneumoniae pneumonia was parallel to that of the complement fixing antibody titer. In two patients, the growth inhibiting antibody titer rose later as compared with the complement fixing antibody titer.
6) It can be concluded that the fermentation inhibition test is a simple and reliable method for the measurement of the growth inhibiting antibody of serum to M. pneumoniae.
7) It was suggested that, when an erythromycin sensitive strain of M. pneumoniae is used in the test, the growth inhibition titer obtained does not always indicate the real growth inhibiting antibody titer in sera from patients under erythromycin-administration.
