Affiliation:
1. Department of Microbiology, Molecular Genetics, and Immunology, University of Kansas Medical Centre, Kansas City, Kansas 66160
Abstract
ABSTRACT
Streptococcus mutans
, a Gram-positive organism, is the primary causative agent in the formation of dental caries in humans. To persist in the oral cavity,
S. mutans
must be able to tolerate rapid environmental fluctuations and exposure to various toxic chemicals. However, the mechanisms underlying the ability of this cariogenic pathogen to survive and proliferate under harsh environmental conditions remain largely unknown. Here, we wanted to understand the mechanisms by which
S. mutans
withstands exposure to methyl viologen (MV), a quaternary ammonium compound (QAC) that generates superoxide radicals in the cell. To elucidate the essential genes for MV tolerance, screening of ∼3,500 mutants generated by IS
S1
mutagenesis, revealed 15 MV-sensitive mutants. Among them, five and four independent insertions had occurred in SMU.905 and SMU.906 genes, respectively. These two genes are appeared to be organized in an operon and encode a putative ABC transporter complex; we designated the genes as
vltA
and
vltB
, for
v
io
l
ogen
t
ransporter. To verify our results,
vltA
was deleted by using an antibiotic resistance marker; the mutant was just as sensitive to MV as the IS
S1
insertion mutants. Furthermore,
vltA
and
vltB
mutants were also sensitive to other viologen compounds such as benzyl and ethyl viologens. Complementation assays were also carried out to confirm the role of VltA and VltB in viologen tolerance. Sensitivity to various drugs, including a wide range of QACs, was evaluated. It appears that a functional VltA is also required for full resistance toward acriflavin, ethidium bromide, and safranin; all are well-known QACs. These results indicate that VltA/B constitute a heterodimeric multidrug efflux pump of the ABC family. BLAST-P analysis suggests that homologs of VltA/B are widely present in streptococci, enterococci, and other important Gram-positive pathogens.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
28 articles.
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