Persistence of Resistance of Tubercle Bacilli to Streptomycin During Passage Through Guinea Pigs

Abstract

Youmans and associates 1 have reported that tubercle bacilli from 8 of 12 patients treated with streptomycin had a resistance to this drug 500 to 1,000 times as great as that of cultures taken before treatment with streptomycin. We have studied cultures from tuberculous patients before and during the course of treatment with streptomycin and also have observed this phenomenon. In some instances cultures of tubercle bacilli have shown a resistance to more than 10,000 times the concentration of streptomycin compared to those obtained prior to treatment.

Preliminary observations indicate that resistance to streptomycin may persist after repeated subculture and storage in the refrigerator. We present herewith our findings that tubercle bacilli isolated from guinea pigs inoculated with sputum, urine or material obtained on gastric lavage from tuberculous patients who were being treated with streptomycin are as resistant as cultures isolated directly from the same materials.

Methods, Specimens of sputum, urine or gastric washings were cultured in 4 tubes of glycerinated egg yolk agar and also inoculated into 2 guinea pigs. Cultures were observed weekly and when growth occurred one tube was selected for determination of resistance to streptomycin. The spleens of the guinea pigs were cultured on the egg yolk agar when the animals died or when they were killed in 8 to 9 weeks. The tests for resistance were done in a manner modified from that used by Youmans and his associates. Two-fold dilutions of streptomycin∗ ranging from 2,000 to 0.04 μg per milliliter of medium were made in Vorwald's modification of Proskauer and Beck's medium containing 10% horse plasma. This was dispensed in 5 ml amounts into 150 by 15 mm test tubes. The inoculum was prepared by grinding in a mortar and suspending a portion of the culture in Proskauer and Beck's medium.