In vitro experiment showing that chemotherapy of tuberculosis by aminoglycoside antibiotics may influence successive chemotherapy with rifampicin

When Mycobacterium tuberculosis strain H37Rv was cultivated in Ogawa egg medium containing 5 micrograms/ml streptomycin and/or 10 micrograms/ml kanamycin, which were considered as subinhibitory, it was observed that growing bacterial population contained several times more rifampicin-resistant mutants than did the parent strain. The ratio of isoniazid-resistant mutants did not change by the above treatment. The finding suggests that, even without the use of rifampicin, the bacterial population of patients becomes more resistant to rifampicin by chemotherapy in the past with streptomycin or kanamycin. Furthermore, it was shown that the ratio of streptomycin-resistant mutants increased by pre-treatment with kanamycin and the ratio of kanamycin-resistant mutants by pre-treatment with streptomycin. Parent, susceptible bacterial population develops 4R-phenotype mutants which are resistant to four drugs, high concentrations of kanamycin, lividomycin and paraomomycin and a low concentration of capreomycin, whereas streptomycin-resistant mutant population does not develop the 4R mutants but develops only mutants with the KR phenotype which is almost mono-resistant to kanamycin.