Table 2.

Phenotypic expression of methicillin resistance of the mutants obtained by selecting N315 with various concentrations of methicillin

Methicillin concn (μg/ml)aNo. of grown coloniesbAppearance rate of resistant mutants (10−4)No. of mutants with each resistance phenotypec
HeteroEagleHomo
4372.961000
8211.68910
1660.48600
3250.40140
6440.32130
12860.48060
25660.48060
51250.04050
  • a Methicillin concentration used for the selection of mutants.

  • b A total of 1.25 × 105 CFU of N315 were inoculated onto the agar plate containing each concentration of methicillin except for that with 512 μg of methicillin per ml, onto which 1.25 × 106 CFU were inoculated.

  • c Each grown colony was picked, colony isolated on a drug-free heart infusion agar plate, grown overnight in drug-free heart infusion broth, and tested for the phenotypic expression of methicillin resistance with population analysis. Ten colonies were arbitrarily picked from each of the plates with 4 and 8 μg of methicillin per ml. Hetero, hetero-type methicillin resistance; Eagle, Eagle-type methicillin resistance; Homo, homo-type methicillin resistance.