Effects of methotrexate on group a beta hemolytic streptococci and streptococcal infection

The incidence of Group A beta hemolytic streptococci and streptococcal infections was lower in children with leukemia than those with no malignancy. Cancer chemotherapy agents were suspected of having some effect on the microbial flora, and methotrexate was investigated. In vitro, methotrexate (MTX) was found to inhibit Group A beta hemolytic streptococci in concentrations of 7.8 μg/ml and less, whereas P. aeruginosa, E. coli, S. aureus, S. marcescens, C. albicans, and Klebsiella‐Enterobacter sp. were resistant to 250 μg/ml. In mice, early death from streptococcal infection was prevented with one injection of MTX, whereas comparable dosage in milligrams of penicillin G failed to protect the animals. These findings indicate that MTX therapy likely influences the incidence of Group A beta hemolytic streptococci and the occurrence of streptococcal infections.