Abstract

"Tolerance" to penicillin in streptococci was investigated by two different techniques. Of 70 strains examined, 35 appeared tolerant in conventional titrations and 31 appeared tolerant when tested by a recently-described disc method. There was 88% agreement between the two methods, but the disc test failed to detect tolerance shown by titrations in six strains of streptococci, including three beta-haemolytic strains belonging to Lancefield's group D. A significant relationship was observed between tolerance and Eagle's optimum dosage effect: 71% of tolerant strains examined displayed the Eagle effect, whereas only 17% of non-tolerant strains exhibited the effect.