Summary: L forms were produced by the penicillin gradient plate technique from four strains of All strains were group B and had various sulphadiazine sensitivities. One parent strain had been propagated for many years in the laboratory, whereas the other three were isolated from recent cases of meningitis. To date, each L form has had more than 60 serial passages on medium containing penicillin. From two strains stabilized L form variants developed on penicillin-free medium following 30 or 40 such passages. Morphological characteristics of these organisms were similar to L forms of other bacteria. Medium and environmental conditions necessary for optimal growth included: brain heart infusion containing a final agar concentration of 1.2% (w/v), sucrose, 10% (w/v), horse serum, 10% (v/v), pH 7.4, temperature 37° and increased CO tension (candle jar). The L forms were non-groupable and had various fermentative reactions, whereas their sensitivity to sulphadiazine was the same as that of their respective parents. Revertants were produced on penicillin-free medium following every tenth serial passage in the L-form state. Sensitivities to sulphadiazine, fermentative reactions and serological groups of the revertant strains were identical with those of their respective parents.


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