Investigation of Persistence Mechanisms in Staphylococcus aureus Bacteraemia Isolates and The Effect of mprF Gain-of-Function Mutations on Global Gene Regulation

Abstract

Staphylococcus aureus (S. aureus) bacteraemia is a major serious bacterial infection. Bacteraemia infections due to methicillin-sensitive S. aureus (MSSA) have increased compared to methicillin-resistant S. aureus (MRSA). Moreover, bacteraemia is complicated due to persistence and failure to respond to treatment by an appropriate antibiotic. However, it is unclear how S. aureus evades the host immune system and displays resistance to antibiotics treatment during persistent bacteraemia (PB). Several bacterial traits/mechanisms were previously associated with persistence. The role of multiple peptide resistance factor (MprF) gain-of-function (GoF) during the development of S. aureus persistence has been previously suggested. MprF is a membrane protein that catalyses the lipid synthesis and the translocation of lysyl-phosphatidylglycerol (L-PG) reducing the negative charge of the bacterial cell surface leading to a charge repulsion for cationic molecules. This study aimed to identify the persistence mechanisms in clinical PB (MSSA) isolates and to investigate the role of mprF GoF mutation P314L in mediating persistence via increased bacterial fitness and the expression of immune and adhesion proteins. This study indicates that mutant MprF P314L has different impacts on protein expression via altering the bacterial cell membrane. Proteomics and transcriptional analysis of PB isolates revealed the impact of mprF P314L mutation on increased expression of virulence genes encoding proteins involved in immune evasion and adhesion and persistence (Eap). This study presented a novel role of MprF in the increased transcription level of virulence genes via impacting the expression of the two main virulence regulators, Sae and Agr. In contrast, the transcription of genes regulated by GraSR or LytSR was not affected suggesting the MprF P314L affects virulence genes/proteins expression on different levels. Overall, our data indicates that MprF mediates the development of persistence through changing global gene regulation leading to persistence traits including increased levels of proteins involved in the evasion and adhesion.