Fig 2.

Investigation of Eagle-type phenotype for methicillin in N315 rpoB(N967I) by Etest. The hetero-type strain (pre-MRSA) N315, homo-type strain ΔIP-H5, and Eagle-type strain N315h4 were used as parent or control strains. The control strains N315, N315ΔIP, ΔIP-H5, and ΔIP-H14 and constructed mutant strain H5 rpoB(I967N) were inoculated with 10⁸ CFU according to the manufacturer's recommendation. N315h4 and N315 rpoB(N967I) strains were inoculated with 10¹¹ CFU. The reason for the inoculation with 10¹¹ CFU was that the double inhibitory zone could be detected more clearly. There is no difference between MIC values with inoculum sizes of 10¹¹ CFU and 10⁸ CFU. An Eagle-type MRSA strain grows better on agar plates containing high concentrations of methicillin than on those with low concentrations of methicillin. The single inhibitory zone was visible with the pre-MRSA N315 and hetero-type MRSA N315ΔIP strains but not, however, with the homo-type MRSA strains.