The effect of permethrin cream on staphylococcal infections and studies on methicillin sensitive and resistant strains of Staphylococcus aureus

Abstract

Antibiotic resistant strains of bacteria are a serious threat to human health. With increasing antibiotic resistance in common human pathogens, fewer antibiotics remain effective. Staphylococcus aureus is a pathogenic bacterium of particular concern to human health as it has developed resistance to many of the currently used antibiotics leaving very few remaining as effective treatment. Alternatives to current conventional antibiotics are needed to allow for the continued treatment of bacterial infections. In addition, a deeper understanding of the characteristics of antibiotic resistant bacteria is needed to allow for an increased ability to properly treat them and to potentially identify targetable changes. To address these two issues, this study aimed at investigating antibacterial activity of an anti-scabies permethrin cream, and examining the lipidomics, proteomics, cell wall thickness and whole-cell surface charge of methicillin sensitive S. aureus (MSSA) and methicillin resistant S. aureus (MRSA). The permethrin cream was found to contain both 5% permethrin and 0.3% formaldehyde and so both were tested alone and in combination for antibacterial activity against MSSA and MRSA. This was done using antimicrobial susceptibility experiments and time-kill assays with viable counts determined using a drop plate method. In addition, any effect of permethrin on cell morphology was investigated using scanning electron microscopy. While permethrin was found to have little effect on bacterial growth and morphology, formaldehyde was found to be capable of inhibiting the growth of both MSSA and MRSA at concentrations found in the permethrin cream as well as four times lower (0.07%) and at 0 hours. Formaldehyde therefore represents a potential alternative treatment for infections with antibiotic resistant bacteria. But for it to be used in this manner the risks associated with it will need to be investigated as there is a lack of literature relating to the effect of dermal application of formaldehyde in humans. The results presented here show that permethrin is a poor inhibitor of bacterial growth but formaldehyde rapidly kills MSSA and MRSA and therefore may serve as an alternative to conventional antibiotics. Additionally, individual strains of MSSA and MRSA were shown to be able to differ from each other beyond the characteristic antibiotic resistance changes. Continued work on this would benefit from examining a wider range of strains and including mutant strains and/or antibiotic challenge to understand how MRSA can change beyond the well characterised expression of penicillin binding protein 2A. This would allow for a deeper understanding into the functioning of S. aureus cells and this can be used to better develop treatments for infections with antibiotic resistant strains of bacteria.

Date of Award	2020
Original language	English