Identification of methicillin-resistant Staphylococcus aureus-specific peptides for targeted photoantimicrobial chemotherapy

Abstract

The increasing prevalence of multi-drug resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), necessitates development of alternative modes of bacterial targeting which are not hindered by antibiotic resistance and minimise collateral damage. To achieve this, the FliTrx™ bacterially-displayed peptide library was panned against MRSA and randomly selected clones (n = 20) were DNA sequenced. One selected peptide was synthesised as both cyclic and linear constructs. Binding of the cyclic construct was observed by flow cytometry against isolates of MRSA whilst the linear construct showed low affinity. Low reactivity was observed with other Staphylococcal sp., Gram-negative bacteria and human keratinocytes. The selected peptide was also cloned in-frame, within the thioredoxin gene into the pPROTet.E 6xHN vector for protein expression. A porphyrin photosensitiser (5-(4-isothiocyanatophenyl)-10,15,20-tris(4-N-methylpyridiniumyl)porphyrin trichloride) was conjugated to the recombinant protein and the in vitro cytotoxic effect of the resulting bioconjugate was determined against MRSA and other non-specific bacterial and mammalian cell lines. Photoantimicrobial chemotherapy (PACT) using the bioconjugate showed a 66% reduction in MRSA growth in comparison with non-irradiated cells. This work demonstrates the potential to isolate peptides with binding specificity against MRSA that can be used for targeted PACT, providing an effective alternative to antibody targeting.