Using checkerboard and time kill assays to determine the effect of antimicrobial compounds against MRSA
Staphylococcus aureus is an important gram-positive bacteria that is commonly found in association with a number of animal hosts, but usually attracts our attention due to it being found in the mucosal cavities of humans(Gajdacs, 2019). Although it often acts as commensal flora, it can become pathogenic(Gajdacs, 2019). This abundance in the environment, as well as the potential to cause serious health complications, makes this bacterium an important pathogen for humans. The acquisition of genes that confer methicillin resistance makes this pathogen (methicillin-resistant S. aureus, or MRSA) even more dangerous(Gajdacs, 2019). Due to the misuse of antibiotics over the decades, these antibiotic-resistant strains are becoming more common(Uzair et al., 2017). In general, one way to counteract this emergence of antibiotic-resistant S. aureus strains is to utilize other antimicrobial compounds, either in conjunction with existing antibiotics or as treatment options by themselves. By pairing antimicrobial compounds, there is the potential for an additive or a synergistic effect against a target pathogen (Ciandrini et al., 2019). This increased effect is more likely if the antimicrobial compounds work on different parts of the cell or interfere with different cellular processes. It also makes it possible for lower quantities of each agent to yield effective antimicrobial action. This is especially important for those cases when there are undesirable side-effects or some degree of toxicity when treating at higher levels. By using both checkerboard and time kill assays, it is possible to explore the nature and magnitude of the inhibitory effect that occurs by treating MRSA with pairs of antimicrobial compounds(Belley et al., 2008; Bonapace, Bosso, Friedrich, & White, 2002). For this project, the compounds that were tested are RE cranberry extract, methylglyoxal, and oregano oil. It is the intent of this project to determine whether pairs of these compounds have a greater inhibitory effect against MRSA when paired than their inhibitory effect against MRSA individually.