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Figure 4.
(a,b) The change in susceptibility of S. aureus strains to
ciprofloxacin (CIP) and vancomycin (VCM) under oxidative stress.
The antibiotic resistance levels were tested in the absence
(-H[2]O[2]) or presence (+H[2]O[2]) of 100  M
H[2]O[2] by a plate sensitivity assay (a) and were also
determined in the absence (-PQ) or presence (+PQ) of 25 M
paraquat by a 96-well plate sensitivity assay (b). Under normal
growth conditions (control) the five strains did not show
noticeable differences. The wild-type strain and the mgrA mutant
strain complemented with pYJ335-His-mgrA showed higher
susceptibility toward CIP and VCM. Under oxidation conditions
both strains showed increased resistance, comparable to that of
the mgrA mutant strain, toward these antibiotics. In control
experiments, the pYJ335-His-mgrAC12S–containing mutant strain
did not change its susceptibility toward CIP and VCM under
normal versus oxidative conditions. (c) Induction of norA, a
gene regulated by mgrA, by oxidative stress.  -Galactosidase
activity of strains containing the norA-lacZ reporter fusion was
determined in the wild-type (Newman) and mgrA mutant (  N
 3040)
strains and expressed in MUG units (MUG, 4-methylumbelliferyl-
-D-galactopyranoside;
1 MUG unit = 1 pmol of MUG cleaved by -galactosidase
per min per OD[600]). Empty bars are untreated cultures. Results
are mean  s.d.
from three independent experiments performed in duplicate.
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