Mechanistic understanding of β-lactam resistance in Staphylococcus aureus.

Antibiotic resistance is a definitive crisis of the 21st century and diseases caused by such organisms are responsible for considerable morbidity and mortality worldwide. Staphylococcus aureus is an opportunistic pathogen capable of colonising a range of niches within the human host. It is more commonly known as its antibiotic resistant derivative, Methicillin Resistant S. aureus (MRSA). MRSA occurs upon acquisition of the ability to express a novel penicillin binding protein PBP2A (mecA), that participates in cell wall biosynthesis and demonstrates a low affinity for beta-lactams, allowing the cells to survive in the presence of antibiotics. Other, chromosomal mutations in genes, called potentiators (pot) are known to be involved in the development of high-level resistant MRSA strains.
My study aimed to characterise the mechanism by which PBP2A confers antibiotic resistance. The bacterial two hybrid system was used to identify PBP2A protein partners that may influence its activity. Random libraries of protein expression constructs did not identify novel interactions for PBP2A. Neither did further directed screening of PBP2A with a range of other proteins involved in cell morphogenesis during growth and division. Importantly my study highlighted the interaction of PBP2A with the endogenous PBP2, whereby the non-native PBP2A may piggyback onto the wide range of PBP2 partners.
High-level resistant MRSA strains that both make PBP2A, and harbour pot mutations can be re-sensitised to the effects of beta-lactams using compounds such as (-)-epicatechin gallate (ECg). I used a directed evolution approach to identify genes involved in the mode of action of ECg. The genes were all functionally associated with nucleotide signalling pathways, highlighting the link between high-level MRSA development and basic cellular physiology. My work has provided novel understanding of the mechanism underpinning MRSA and new avenues to develop adjunct approaches to rationally develop new control regimes, to beat MRSA.