The development of novel antimicrobial peptides with activity against MRSA

MRSA is a significant pathogen, which can cause a range of minor and major infections both in the hospital and community environments. MRSA is developing resistance to many antibiotics, including vancomycin, which is now the first choice antibiotic to treat MRSA infections in the UK. This together with the dearth of new antibiotics being introduced could see the emergence of untreatable S. aureus strains. This has led to renewed interest in alternative antimicrobial agents. Lysostaphin is an endopeptidase produced by Staphylococcus simulans biovar staphylolyticus, which cleaves the peptidoglycan cross-bridges of other staphylococcal species. Lysostaphin has been investigated as a potential therapeutic agent and has shown promise in in vitro and in vivo studies and in clinical trials. However, resistance to lysostaphin is likely to emerge and there will be a demand for second generation Iysostaphins and/or other similar novel antimicrobials that can counteract this resistance. This study describes the cloning, purification and assaying of an endolysin of the S. aureus P68 bacteriophage. Lys16 lysin has previously been shown to possess staphylolytic activity. This study demonstrates that the purified recombinant protein is poorly soluble and is inactive against live cells. The Atl autolysin of S. aureus was also investigated as a potential antimicrobial. This study confirmed the hydrolytic profiles of the enzymes, and a chimeric peptide incorporating the lysostaphin targeting domain with the Atl glucosaminidase was designed. This did not confer greater activity against S. aureus, although the targeting domains of each enzyme were shown to utilise different cell surface receptors. Finally, this study reports the development of a novel assay to measure the activity of antimicrobial peptides against S. aureus, using a bioluminescence reporter. This was shown to be a sensitive assay, able to distinguish small differences in the activity of antimicrobial peptides