Scientific
Publications - Work Done by Microbiology Reader Bioscreen C
Mirjana Macvanin, Andras Ballagi, and Diarmaid Hughes,
Fusidic Acid-Resistant Mutants of Salmonella enterica Serovar
Typhimurium Have Low Levels of Heme and a Reduced Rate of Respiration and Are
Sensitive to Oxidative Stress, Antimicrobial Agents and Chemotherapy,
October 2004, p. 3877-3883, Vol. 48, No. 10
ABSTRACT
Mutations in the translation elongation factor G (EF-G) make Salmonella enterica
serovar Typhimurium resistant to the antibiotic fusidic acid. Fusr mutants are
hypersensitive to oxidative stress and rapidly lose viability in the presence of
hydrogen peroxide. We show that this phenotype is associated with reduced
activity of two catalase enzymes, HPI (a bifunctional catalase-hydroperoxidase)
and HPII (a monofunctional catalase). These catalases require the iron-binding
cofactor heme for their activity. Fusr mutants have a reduced rate of
transcription of hemA, a gene whose product catalyzes the first committed step
in heme biosynthesis. Hypersensitivity of Fusr mutants to hydrogen peroxide is
abolished by the presence of -aminolevulinic acid, the precursor of heme
synthesis, in the growth media and by the addition of glutamate or glutamine,
amino acids required for the first step in heme biosynthesis. Fluorescence
measurements show that the level of heme in a Fusr mutant is significantly lower
than it is in the wild type. Heme is also an essential cofactor of cytochromes
in the electron transport chain of respiration. We found that the rate of
respiration is reduced significantly in Fusr mutants. Sequestration of divalent
iron in the growth media decreases the sensitivity of Fusr mutants to oxidative
stress. Taken together, these results suggest that Fusr mutants are
hypersensitive to oxidative stress because their low levels of heme reduce both
catalase activity and respiration capacity. The sensitivity of Fusr mutants to
oxidative stress could be associated with loss of viability due to iron-mediated
DNA damage in the presence of hydrogen peroxide. We argue that understanding the
specific nature of antibiotic resistance fitness costs in different environments
may be a generally useful approach in identifying physiological processes that
could serve as novel targets for antimicrobial agents.
(Abstract
online)
