Abstract
Antibiotic resistant Staphylococcus aureus (S. aureus) includingmethicillin resistant S. aureus (MRSA) and vancomycin intermediate resistant
S. aureus (VISA) are a major concern in world health care. MRSA is one of the
most prevalent pathogens and causes severe infections in hospital and
community settings. It is responsible for over 300,000 cases of MRSA infection
globally every year. Though significant progress has been made in drug
discovery, few novel antibiotics have been developed in the last decade or so.
Reasons for this are partly because new targets are hard to find, partly because
they are expensive to develop and partly because they come with a low return
on investment and because there is extremely fast development of resistance
even to new antimicrobials. This research aims to explore novel therapeutic and
mechanistic approaches focused on cell wall regulation that overcome
resistance.
Following a detailed investigation, a β-lactam enhancer was identified
and investigated for its mechanism of action in MRSA. It was observed that
chemical 1 showed a strain-dependent and antibiotic-dependent enhancement
in multiple MRSA strains. Mechanistic investigation demonstrated that chemical
1 reduced the availability of D-Ala-D-Ala precursor and altered the autolytic
activity in MRSA strains. This suggested disruption of the cell wall potentially by
reducing D-alanine availability.
The second approach focused towards understanding the development
of resistance in VISA strains. The VISA resistance phenotypes are often
associated with mutations in two-component system like WalKR. This study
made an attempt to investigate biochemical mechanism of the mutations in
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causing the resistant phenotypes. The wild-type WalK and WalR proteins were
successfully expressed and purified for future biochemical characterization.
Together, these results point to the importance of cell wall regulation in
antibiotic resistance and show the promise of targeting the physiology and
regulatory mechanisms of bacteria. This work offers a platform for developing
new treatments based on adjuvants that will restore the efficacy of existing
antibiotics.