Usefulness of an erythromycin-resistant strain of Mycoplasma pneumoniae for the fermentation-inhibition test.

The fermentation-inhibition (FI) test for Mycoplasma pneumoniae was performed with two strains of M. pneumoniae, one susceptible to erythromycin and one highly resistant to erythromycin with cross-resistance to other macrolide antibiotics. Serum titers in children with M. pneumoniae pneumonia who received no antibiotic were similar with the two strains. Children with atypical pneumonia with a transient rise in the FI titer with the susceptible strain proved to have received erythromycin at the time of the rise. They showed no rise in the FI titer done with the erythromycin-resistant strain. Oral administration of erythromycin regularly elevated the serum FI titer when the test was done with the susceptible strain. Use of the resistant strain in the test eliminated this false elevation. Tetracycline and chloramphenicol did not elevate the titer, even with the susceptible strain. Use of the strain of M. pneumoniae resistant to erythromycin provides a true FI antibody serum titer, avoiding the influence of antibiotics.