Role of mgrA and sarA in Methicillin-Resistant Staphylococcus aureus Autolysis and Resistance to Cell Wall-Active Antibiotics
MRSA, mgrA, sarA, and Autolysis ● JID
Role of mgrA and sarA in Methicillin-Resistant Staphylococcus aureus Autolysis and Resistance to Cell Wall-Active Antibiotics
María Pilar Trotonda 2
Yan Q. Xiong () 0 1
Guido Memmi 2
Arnold S. Bayer 0 1
Ambrose L. Cheung 2
0 David Geffen School of Medicine at UCLA , Los Angeles, California
1 Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA , Torrance
2 Department of Microbiology, Dartmouth Medical School , Hanover, New Hampshire
Background. We have previously shown the importance of mgrA and sarA in controlling autolysis of Staphylococcus aureus, with MgrA and SarA both being negative regulators of murein hydrolases. Methods. In this study, we analyzed the effects of mgrA and sarA on antibiotic-mediated lysis in vitro and on the responses to cell wall-active antibiotic therapy in an experimental endocarditis model by use of 2 representative MRSA strains: the laboratory strain COL and the community-acquired clinical strain MW2. Results. We found that mgrA and sarA independently down-regulated sarV (a marker for autolysis), although the alteration in sarV expression did not correlate directly with the autolysis profiles of single mgrA and sarA mutants. Importantly, the mgrA/sarA double mutants of both strains were more autolytic than the single mutants in vitro. We demonstrated that, despite equivalent intrinsic virulences of the parent strains and their isogenic mgrA/sarA double mutants in the endocarditis model, oxacillin and vancomycin treatment of the mgrA/sarA double mutants yielded significant reductions in vegetation bacterial densities in vivo, compared with treatment of their respective parent strains. Conclusions. These results suggest that down-regulation of mgrA/sarA in combination with use of cell wall-active antibiotics may represent a novel approach to treat MRSA infections.
Staphylococcus aureus is an opportunistic pathogen that
can cause a broad spectrum of human infections [1, 2].
Recent reports of methicillin-resistant S. aureus (MRSA)
strains with resistance to newer antibiotics have
highlighted the increasing threat to public health posed by
MRSA [3–5]. The virulence of S. aureus is generally
attributable to a diverse array of pathogenetic factors
[6 – 8]. The coordinated expression of these virulence
determinants has been shown to be controlled by
multiple genetic loci, including 2-component regulatory
systems and global transcriptional regulators [6 –13].
Besides their roles in virulence, some of the
aforementioned regulators (e.g., SarA, SarV, and MgrA) have also
been found to control autolysis in S. aureus [7, 11–15].
The integrity of the cell wall is generally maintained by
2 competing processes: cell wall synthesis and cell wall
lytic activity. The enzymes involved in the synthesis of
peptidoglycan, the major component in the cell wall of S.
aureus, are penicillin-binding proteins 1– 4, which have
been traditional targets for antimicrobial therapy (e.g.,
penicillins and cephalosporins). Autolysis, on the other
hand, is mediated by autolytic enzymes (also called
“autolysins” or “murein hydrolases”), which cleave the
covalent bonds that confer stability to the cross-linked
peptidoglycan chain in order to form the rigid cell wall.
An imbalance between synthesis and lysis can lead to cell
death, as has been the case with penicillin-induced lysis,
wherein cell wall synthesis is disrupted while lytic
activity remains unchecked.
Available data support the notion that murein
hydrolases are controlled by global regulators. For instance,
sarA and mgrA repress the expression of autolysins,
whereas sarV promotes their expression [14, 16].
Additionally, we have shown that both sarA and mgrA
downStrain or plasmid
Mutant strain of 8325–4 that accepts foreign DNA
agr laboratory strain related to 8325–4
Methicillin-resistant laboratory strain SCCmec type I; MLST ST250; spa type YHGFMBQBLO; agr group I;
TSST-1 ; pvl ; splE ; cna ; seb sec ; seh
Community-associated methicillin-resistant laboratory strain SCCmec type IVa; MLST ST1; spa type
UJJJJFE; agr group III; TSST-1 ; pvl ; splE ; cna ; seb sec ; seh
COL with a sarA::kan mutation
mgrA/sarA mutant in COL
COL with a sarV::ermC mutation
COL with pALC2366
COL with pALC2489
MW2 with a sarA::kan mutation
mgrA/sarA mutant in MW2
MW2 with pALC2366
MW2 with pALC2489
Host strain for cloning
regulate sarV, which can serve as a marker of murein hydrolase
activity . Thus, inhibition of mgrA and sarA could
conceivably enhance bacterial lysis and, in conjunction with cell wall–
lytic agents, might augment the net bactericidal effect.
In this study, we investigated the role of mgrA and sarA in
autolysis and resistance to 2 cell wall–active antibiotics, oxacillin
and vancomycin, in 2 MRSA strains, COL and MW2.
MATERIALS AND METHODS
Bacterial strains, plasmids, and genetic manipulations in
Escherichia coli and S. aureus. The phenotypic and genotypic
properties of 2 representative MRSA strains, the laboratory
strain COL and the community-acquired clinical strain MW2,
and the plasmids used in this study are listed in table 1. Standard
molecular biology and recombinant DNA techniques were used
as previously described [17, 26, 27].
The sarA and sarV genes were inactivated in S. aureus COL and
MW2 by transducing sarA::kan and sarV::ermC mutations,
respectively, using phage 11. To construct mgrA mutants, we used PCR
to amplify 2 fragments flanking the gene sequences to be deleted.
The PCR primers yielded a complementary region of at least 16
bases, allowing the first PCR product (the left fragment) to anneal to
the second PCR product (the right fragment); a second PCR
reaction was performed using products of the first PCR reaction, to
obtain a single fragment. The fusion product was purified, digested
with SmaI, and ligated into the temperature-sensitive shuttle
plasmid pMAD . Allelic exchange in the absence of selection
markers was performed [28, 29].
Determination of minimum inhibitory concentrations
(MICs). MICs of oxacillin and vancomycin were determined
using cation-supplemented Mueller-Hinton broth according to
Clinical and Laboratory Standards Institute guidelines .
Impact of oxacillin on growth of COL and MW2 and their
isogenic mutants. To assess the susceptibility of mgrA, sarA,
and double mutants of COL and MW2 to oxacillin, bacterial
cultures were incubated overnight, and supernatants were
diluted into fresh TSB to yield a starting OD600 of 0.05. Oxacillin
was added at sub-MIC concentrations. The mixtures were then
incubated with shaking at 37°C, with the OD600 measured hourly
for 7 h.
Impact of Triton X-100 and oxacillin on cellular lysis of
COL and its isogenic mutants. To eliminate possible
variations due to growth in nutrient media, Triton X-100 and
oxacillin were used to lyse the COL strain set . In brief, overnight
cultured strains were adjusted to an OD580 of 0.7, washed,
exposed to 50 mmol/L of Tris-HCl (pH 7.2) containing 0.05% of
Triton X-100 or 1/10 MIC of oxacillin, and incubated at 30°C
with agitation. Cellular lysis was measured by determining the
changes in OD580.
Zymographic analysis. To detect extracellular murein
hydrolases, SDS-PAGE– based zymographic analysis was
performed with modifications . In brief, overnight cultures of S.
aureus strains were diluted and grown at 37°C with shaking (250
rpm) in TSB until reaching an OD650 of 0.7. The supernatants
were harvested, concentrated, and analyzed for protein
concentrations with the Bradford assay (BioRad). Equivalent amounts
of extracellular proteins were electrophoretically resolved on an
8% SDS–polyacrylamide gel containing either lyopholized cells
of Micrococcus lysodeikticus or S. aureus RN4220, after which
they were washed and incubated overnight at 37°C with
agitation. Gels were then stained with 0.1% methylene blue (Sigma),
with the clear bands indicating regions of murein hydrolase
Transcriptional fusion of the sarV promoter. To confirm
the effect of mgrA and/or sarA mutations on sarV promoter
activity, we used plasmid pALC2489, which contains the sarV
promoter that drives the gfpuvr reporter gene (table 1). The plasmid
was introduced into COL and MW2 strain sets. For the assay, S.
aureus strains were diluted in TSB containing chloramphenicol
(10 g/mL) and grown at 37°C. Aliquots were assayed for cell
density (at OD650) and fluorescence in a FL600 fluorescence
reader (BioTek Instruments). Promoter activation was plotted
as mean fluorescence/OD.
Purification of SarV and production of anti-SarV
antibody. The 351-bp sarV coding region was amplified by PCR,
using strain RN6390 chromosomal DNA as the template, and then
was cloned into the NdeI and BamHI site of expression vector
pET14b (Novagen) and transformed to E. coli BL21(DE3)pLysS.
Recombinant protein expression was induced by adding 1 mmol/L
of ITPG to a growing culture. After a 4-h period of growth at 37°C,
cells were harvested and resuspended in binding buffer, frozen,
thawed overnight, and sonicated. Clarified supernatant was applied
to a nickel affinity column (Novagen) and eluted with 1 mol/L of
imidazole. The authenticity and purity of SarV were confirmed by
N-terminal sequencing and Coomassie brilliant blue staining of an
SDS–polyacrylamide gel containing the protein.
To raise polyclonal sera, 50 g of SarV in complete Freund’s
adjuvant was injected subcutaneously into mice. This was
followed by biweekly immunization (50 g) in incomplete
adjuvant and serial testing of sera with strips of immunoblot
containing 5 ng of SarV. When the anti-SarV antibody titer in serum
reached 100,000 against preimmune serum, animals were
sacrificed and blood was collected.
Western blot analysis. Cellular extracts were obtained from
bacteria grown overnight in the presence of a hypertonic buffer
containing lysostaphin (12.5 g/mL; AMBI), PMSF,
iodoacetamide, and DNase. The pellet was lysed, and the supernatant was
harvested. Equivalent amounts of supernatant proteins (40 –50 g
each) were resolved in 16% SDS–polyacrylamide gels, blotted onto
Immobilon P membrane (Millipore) and blocked . The blot
was incubated for 2 h with serum containing anti-SarV antibody
(dilution, 1:8000), washed, and further incubated for 1 h with
antimouse peroxidase-conjugated secondary antibodies diluted to
1:10,000 (Pierce). Blots were developed using the enhanced
chemiluminescence system ECL Plus (Amersham Bioscience).
Rabbit endocarditis model. To determine whether there is
a linkage between in vitro autolysis profiles and improved
therapeutic outcomes with cell wall–active agents in vivo, a rabbit
endocarditis model was used . In brief, anesthetized rabbits
(New Zealand white [Irish Farms]) underwent
transcarotidtransaortic valve catheterization. Twenty-four hours after
catheterization, rabbits were inoculated intravenously with different
S. aureus strains at the inoculum of interest. All rabbits were
treated in accordance with institutional and US Public Health
Service guidelines for the humane care and treatment of animals.
We compared the virulence of COL and MW2 parent strains
with their respective mgrA/sarA double mutants, using inocula
of 104, 105, or 106 cfu/animal. As established by pilot studies,
these inocula encompass the ID95 for inducing endocarditis.
Twenty-four hours after infection, rabbits were sacrificed for
microbiological evaluation (see below).
Before therapeutic experiments were performed,
pharmacokinetic profiles of oxacillin (intramuscular doses of 50 or 100
mg/kg) and vancomycin (an intravenous dose of 7.5 mg/kg)
were investigated. These doses represent strategies used in
previous studies of experimental S. aureus endocarditis [33, 34].
Oxacillin and vancomycin serum concentrations were
determined by agar diffusion assays, using S. aureus RN6390 and
Bacillus subtilis ATCC 6633, respectively . The limit of
detection for these bioassays was 1 g/mL for each antibiotic.
Twenty-four hours after infection, rabbits were randomized
to receive no therapy, oxacillin (50 or 100 mg/kg
intramuscularly 3 times/day), or vancomycin (7.5 mg/kg intravenously 2
times/day). Treatment was given for 3 days. These dose strategies
were based on pharmacokinetics data and were intentionally
designed to achieve peak serum levels that were approximately at
or below the MICs for these agents, to divulge the potential
combined impacts of autolysis enhancement plus cell wall–active
Control rabbits were sacrificed 24 h after receipt of the
infective inoculum. Antibiotic-treated rabbits were sacrificed 24 h
after receipt of the last antibiotic dose. At sacrifice, all aortic valve
vegetations were removed and quantitatively cultured.
Statistical comparisons. For comparison of in vivo
microbiologic data, Kruskal-Wallis analysis of variance with post hoc
correction for multiple comparisons was used.
Impact of oxacillin on growth of the COL and MW2 parent
strains and their isogenic mutants. The oxacillin MICs for
COL and MW2 were 256 and 32 g/mL, respectively. The MIC
of vancomycin was 2 g/mL for both strains. For the COL strain
set exposed to 25 and 50 g/mL of oxacillin (representing 1/10
and 1/5 MIC, respectively, for the parent strain), both mgrA
and sarA single mutants exhibited decreasing ODs, compared
with the parent. Remarkably, the mgrA/sarA double mutant
exhibited the greatest decrease in growth, compared with the other
strains (figure 1A). The mgrA/sarA double mutant of MW2 also
exhibited the most potent growth inhibition in the presence of
oxacillin at fractions of the MIC, compared with the parent
strain and mgrA single mutant (figure 1B).
Impact of Triton X-100 and oxacillin on cellular lysis of the
COL parent strain and its isogenic mutants. In the presence
of Triton X-100, only 40% of the COL parent cells and 60% of
the single mutant cells lysed 7 h after incubation (figure 2A).
However, 80% of the mgrA/sarA double mutant cells lysed in
Figure 2. Autolysis induced by Triton X-100 (A) and 1/10 MIC of
oxacillin (B) over time at 30°C in the parent methicillin-resistant
Staphylococcus aureus COL strain ( ) and its mgrA mutants ( ),
sarA mutants (‘), and mgrA/ sarA mutants ( ).
the presence of Triton X-100 (figure 2A). For oxacillin-induced
autolysis, the mgrA/sarA double mutant had the highest lysis
rates, compared with the single mutants and parent strain
Effect of mgrA and/or sarA on expression of autolysins in
strains COL and MW2. The major known autolysin, Atl, is
proteolytically cleaved to generate a 62-kDa amidase and a
51kDa glucosaminidase . M. lysodeikticus (figure 3A and 3C)
and S. aureus RN4220 (figure 3B and 3D) were used because they
are susceptible to glucosaminidase and amidase, respectively
[31, 37]. As shown in figure 3A and 3C, the sarA mutants of COL
and MW2 displayed a reduction in the level of Atl ( 115 kDa),
accompanied by enhanced glucosaminidase ( 51 kDa) and
amidase ( 62 kDa) activity, compared with parent strains. The
identity of amidase was confirmed by increased lytic activity with
the 62-kDa band in RN4220 (figure 3B and 3D). Of note, the
double mgrA/sarA mutants displayed a zymographic profile
similar to that of the sarA mutants. Interestingly, the mgrA mutant
only showed unprocessed Atl and glucosaminidase activities. Of
interest, neither the sarV mutant nor the sarV hyperexpression
mutant had increased glucosaminidase or amidase activity,
compared with the respective parent strains.
Lytic activity of mgrA/sarA double mutants is probably
independent of sarV expression. As shown in figure 4A, both
mgrA/sarA double mutants had higher sarV promoter activation
than the single mutants and respective parent strains.
Interestingly, the impact of the mgrA mutation on sarV expression was
higher than that observed for the sarA mutant, which exhibited a
level of sarV activation similar to that of the parent strain. Given
that MgrA and SarA can bind to the sarV promoter  and that
there is a differential effect on sarV expression by these 2
regulators, we also evaluated autocrine regulation by assaying for
sarV promoter activation in sarV mutants; however, we were
unsuccessful in detecting any evidence of autocrine regulation
with this assay (data not shown).
Concordant with results of the promoter fusion assays, the
double mgrA/sarA mutants expressed a higher level of SarV than
their respective parent strains (figure 4B). However, in contrast
to the results of the promoter fusion assay, the mgrA mutant did
not express a higher level of SarV than the parent strain (figure
4B). Similarly, the sarA mutants also expressed a lower level of
SarV than the respective parent strains. We included the
corresponding sarV mutant as a negative control and the parent strain
carrying a shuttle plasmid expressing sarV (the sarV
hyperexpressor) as a positive control (figure 4). In comparing these data
(figure 4B) with those of transcriptional fusion assay, in which
the sarV promoter expression was higher in the mgrA mutant
than the parent strain (figure 4A), it seems clear that other
factors must be involved in the translational or posttranslational
regulation of SarV in the mgrA mutant. Additionally, the level of
SarV production in the sarA mutants also did not correlate with
the lytic activity wherein the sarA mutant exhibited increased
autolytic activity (figure 3). Moreover, hyperexpressing SarV
strains did not demonstrate enhanced autolytic activity upon
zymogram analysis (figure 3). Thus, SarV appears to be a marker
of autolysis, whereby one can follow the autolytic activity of the
double mutant, although the level of SarV itself is not the
determining factor for enhanced lytic activity of the double mutants
in strains COL and MW2.
Pharmacokinetics of oxacillin and vancomycin in the
rabbit endocarditis model. After a single 100-mg/kg dose of
oxacillin, serum oxacillin levels peaked at 27 g/mL, a
concentration well below the MICs for COL and MW2. The peak serum
level for vancomycin (7.5 mg/kg) was 3 g/mL, which was
slightly higher than the MICs for each strain, but the level rapidly
decreased below the MICs. The half-lives of oxacillin and
vancomycin were 30 and 120 min, respectively.
In vivo role of mgrA and sarA in the efficacy of cell wall–
active antibiotics in the endocarditis model. The efficacies of
oxacillin and vancomycin against the COL strain and its mgrA/
sarA double mutant (challenge dose, 105 cfu) in the model are
presented in table 2. We focused our in vivo studies on
comparing the parent strains and mgrA/sarA double mutants, because
the outcomes of in vitro comparisons were maximally distinct in
these 2 organism groups. At 100 mg/kg of oxacillin and 7.5
mg/kg of vancomycin, a significant reduction in S. aureus
vegetation densities was observed in animals infected with the mgrA/
sarA double mutant, compared with the untreated double
mutant. In contrast, in infection with the parent COL strain, neither
oxacillin nor vancomycin treatment yielded any significant
reduction in vegetation densities.
For strain MW2, we used a lower oxacillin dose (50 mg/kg)
because of the substantially lower MIC, compared with that for
the COL strain. This oxacillin regimen yielded a modest
reduction in bacterial vegetation densities in the parent MW2 strain
(table 3). Importantly, this treatment caused a reduction of
6 log10 cfu per g of vegetation. in animals infected with the
mgrA/sarA double mutant, compared with untreated controls.
Similar to the COL strain, vancomycin treatment significantly
reduced the vegetation densities of the double mutant,
compared with findings for untreated double mutant controls and in
vancomycin-treated animals infected with the parent MW2
There were no significant differences in the intrinsic virulence
between the parent COL and MW2 strains and their respective
mgrA/sarA double mutants in the absence of antibiotics at
challenge levels of 104, 105, and 106 cfu (data not shown for 104 and
It has been shown that mgrA and sarA, both of which are global
regulators of virulence determinants [7, 12, 16, 38], are also
negative regulators of autolysis . In this study, we extended these
findings to ascertain the role of MgrA and SarA in the control of
MRSA autolysis and its impact on in vivo antibiotic efficacies.
Several interesting observations emerged from the present
investigations. For example, we found that concomitant presence
of mgrA and sarA mutations led to an enhanced
oxacillinmediated autolytic phenotype, compared with the presence of
either mutation alone, in both MRSA strains in vitro. More
important, our studies emphasized a significant enhanced
bactericidal effect of cell wall–active antibiotics in mgrA/sarA double
mutants of strains COL and MW2 in a well-characterized
endocarditis model. The mechanisms of enhanced oxacillin-induced
cell autolysis in the double mutants of these 2 MRSA strains are
not precisely defined by our studies. However, previous
observations and data in this study enable us to piece together a
putative network of genes that help explain our findings. From recent
investigations , it is known that MgrA positively regulates
lytRS and arlRS, two 2-component regulatory systems that
repress expression of autolysins. LytRS is also a positive regulator
of LrgA , a putative antiholin molecule that interferes with
the function of the putative holin molecule CidA . The holin
protein has been found to form pores in the cell membrane that
S. aureus density,
log10 cfu/g of vegetation
NOTE. The challenge inoculum of each strain was 105 cfu.
a Denotes comparison with untreated controls.
Table 3. Efficacies of oxacillin and vancomycin against Staphylococcus
aureus strain MW2 and its mgrA/sarA double mutant in an experimental
rabbit endocarditis model.
S. aureus density,
log10 cfu/g of vegetation
NOTE. The challenge inoculum of each strain was 105 cfu.
a Denotes comparison with untreated controls.
b P .05, compared with the oxacillin-treated MW2 parent group.
c P .05, compared with the vancomycin-treated MW2 parent group.
enable murein hydrolase export from the cytosol to the cell wall.
Accordingly, we speculate that an mgrA mutation would lead to
down-regulation of LrgA and ArlRS, which would, in theory,
increase the expression of murein hydrolases. However,
zymogram analysis of the mgrA mutant failed to reveal a significant
overall effect on the expression of major autolysins, compared
with the parent strains (figure 3). Of importance, however, the
mgrA mutants were more likely than the parent strains to be
autolytic in the presence of oxacillin (figure 1). In contrast, the
sarA mutants (which displayed increased autolysin expression
on zymograms) also exhibited augmented autolysis in the
presence of oxacillin concentrations below the MIC, compared with
the mgrA mutants and the parent strains (figure 1). Remarkably,
the double mutants were clearly more autolytic than either single
mutant at oxacillin concentrations below the MIC, and they also
expressed a greater level of autolysins than their respective
parent strains (figures 1 and 3). On the basis of these data, we
speculate that the synergistic autolytic activity of the double
mgrA/sarA mutants may be due to a combination of factors
individually contributed by mgrA and sarA, including the complex
regulation of genes in the net autolytic cascade and the
production of autolysins.
Additionally, we analyzed the impact of sarV, a positive
regulator of autolysis that is repressed by sarA and mgrA .
Although the double mutants clearly demonstrated an increased
level of sarV expression (figure 4), enhanced expression of sarV
by itself is not enough to initiate significant autolysis. Thus, an
mgrA mutant that displayed elevated sarV expression (figure 4)
neither significantly increased oxacillin-induced autolysis
(figure 1) nor produced increased levels of autolysins (figure 3). This
lack of correlation between sarV gene expression and autolysin
expression in mgrA mutants may, in part, be due to subsequent
translation of sarV; thus, despite expression of greater levels of
sarV promoter (figure 4A), the mgrA mutants did not produce
increased levels of SarV, compared with the parent strains
(figure 4B). Nonetheless, we could not rule out the possibility that
the stability of SarV may have been altered in the mgrA mutants.
Given that protease expression is generally down-regulated in an
mgrA mutant as a result of lower agr expression [10, 41], a
reduction in the SarV level in mgrA mutants cannot be attributable
to augmented proteolytic activity.
Oxacillin-induced lysis is dependent on murein hydrolase
activity . This class of antibiotics (i.e., cell wall–active antibiotics) can
exert a potent bactericidal effect without lysis in mutants lacking
murein hydrolases . Conversely, the lytic effect of oxacillin
might be enhanced in mutants with an elevated level of murein
hydrolases (e.g., mgrA/sarA strains). Such an event in vitro could be
translated into an augmented therapeutic efficacy of oxacillin in
treating MRSA infections. Indeed, we found this to be true in both
mgrA/sarA double mutants, compared with their respective parent
strains, by use of the endocarditis model. In this model, clearance of
the organism from infected heart valves is principally dependent on
the bactericidal effects of the antibiotics, without substantial
contributions from the adaptive immune system [42, 43]. Our studies
emphasized the enhanced effect between autolysis regulatory
mutants and oxacillin. Thus, in endocarditis caused by COL and MW2,
which are normally resistant to oxacillin, a mgrA/sarA double
mutation significantly enhanced the bactericidal effect of oxacillin in
vivo, presumably because of enhanced lysis in the double mutant,
even at sub-MICs of an antibiotic to which it is resistant. This
enhanced in vivo bactericidal effect between the mgrA/sarA double
mutants of strains COL and MW2 and cell wall–active antibiotics
was also confirmed using vancomycin therapy in the same model.
Of note, such significant enhanced impacts of oxacillin or
vancomycin in vivo were not observed in single mutants (data not
shown). Importantly, comparative virulence assessments showed
that both parent strains and their respective double mgrA/sarA
mutants retained equivalent intrinsic virulence.
In summary, these investigations may open up a new avenue
to MRSA infection therapeutics. Given that MgrA and SarA are
both dimeric winged helix proteins [44, 45] and that an
inhibitory small molecule (e.g., virstatin) has been found to disrupt the
dimerization and function of ToxT in Vibrio cholerae , it is
conceivable that targeting a common functional domain
between these 2 proteins with a small synthetic molecule(s) may
represent a novel strategy to enhance the effectiveness of
oxacillin and other cell wall–lytic agents against MRSA.
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