exposure of a penicillin-sensitive type 2 strain ( mic , 0.006 microgram/ml ) to sequentially increasing concentrations of penicillin allowed the isolation of spontaneous resistant mutants with stepwise increases in the mic of penicillin required ( 0.01-0.02 , 0.025-0.05 , and 0.1 microgram/ml ) , and in these laboratory isolates too , pbp groups 1 and 2 showed decreased affinity for labeled benzylpenicillin .
C0030842
penicillin
C0030827
benzylpenicillin