Detection of penicillin tolerance in streptococci

"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.