Testing the Effects of Branched Poly(ethylenimine) and Ampicillin On Methicillin-resistant Staphylococcus Aureus Biofilms

Abstract

Methicillin-resistant Staphylococcus aureus, or MRSA, is a difficult to treat infection of both medical implants and wounds. This type of S. aureus is characterized by its resistance to beta-lactam antibiotics or those antibiotics that are derivatives of penicillin. The bacteria have an altered protein, PBP2a which is a mutated form of PBP that non-resistant strains use. MRSA strains can easily form biofilms compounding the effects of clinical treatment. They first create a physical barrier to prevent antibiotics from reaching the bacteria. The bacteria within the biofilms also have switched to a non-dividing nature or solitary lifestyle, most antibiotics only work effectively against actively dividing bacteria. Branched poly(ethylenimine), or BPEI, has shown to re-sensitize MRSA to the beta-lactam antibiotics. This occurs by targeting teichoic acid, a molecule PBP2a needs to properly function, leaving it vulnerable to beta-lactam targeting. Using a checkerboard assay, high molecular weight BPEI was tested for any synergistic antibiofilm effect when combined with ampicillin against MRSA biofilms. Results show that at a combination of 128 ug/ml of both BPEI and ampicillin results in a reduction in biomass. ANOVA testing indicates that BPEI and ampicillin individually have a significant effect on the biomass reduction of the biofilms but together are not significant. These results indicate further replicate trials are needed to further investigate the relationship between BPE