The effect of Plectranthus aliciae (Codd) Van Jaarsv. & T.J. Edwards on quorum sensing of bacteria associated with acne vulgaris

Abstract

The World Health Organization has raised concerns of antibiotic resistance threatening the global health care system and economy. Antibiotic resistance results from quorum sensing mechanisms that allow bacterial species to express genes associated with biofilm formation, protecting sessile cells from well-known antibiotic therapies. Increased antibiotic resistance is observed in maladies such as acne vulgaris, prosthetic implant-associated infections, and wounds due to the presence of pathogenic bacteria, including Cutibacterium acnes and Staphylococcus epidermis. However, controversy exists regarding the type of relationship between these bacteria and their role in these maladies. More research is required to understand better the pathogenic relationship of these bacteria and their role in the progression of antibiotic resistance. Furthermore, there is a need for new alternative therapies that target quorum sensing mechanisms and circumvent antibiotic resistance increasing the efficiency of treatments for acne vulgaris, prosthetic implant-associated infections and wounds. This study investigated the quorum sensing relationship of C. acnes (ATCC® 6919) and S. epidermidis (ATCC® 35984) in order to determine the combined virulent effect of these bacteria in a multispecies system under various growth conditions. Furthermore, this study investigated the potential use of Plectranthus aliciae (Codd) Van Jaarsv. & T.J. Edwards, an indigenous South African plant, its identified pure compounds and fractions for targeting quorum sensing mechanisms. The targeted mechanisms include the release of autoinducer-2 (AI-2), biofilm attachment and formation, lipase production, extracellular DNA release and potential wound healing activity. The potential use of nanoparticles synthesised from P. aliciae ethanolic extract and pure compounds to target biofilm attachment and formation inhibit the bacterial systems of interest and contribute to wound healing. It was determined that C. acnes (ATCC® 6919) and S. epidermidis (ATCC® 35984) has a synergistic relationship. Under aerobic conditions, an increase in biofilm density, lipase and eDNA production was observed. This supported the hypothesis that S. epidermidis (ATCC® 35984) provides a safe environment for C. acnes (ATCC® 6919) to thrive under aerobic conditions. Plectranthus aliciae, its pure compounds and fractions, targeted the various quorum sensing mechanisms, including the release of AI-2, lipase inhibition, bacterial inhibition, biofilm attachment and formation, and eDNA production. Noteworthy wound healing activity was observed for P. aliciae ethanolic extract and the synthesised nanoparticles of rosmarinic acid. This study is the first report of the synergistic quorum sensing relationship between C. acnes (ATCC® 6919) and S. epidermidis (ATCC® 35984) in a multispecies system. This could be an indication that the pathogenic relationship between these bacteria is strain-specific and supports the hypothesis of the current study. To conclude, this is the first report of P. aliciae, its partitions and newly identified compound luteolin targeting quorum sensing processes of C. acnes (ATCC® 6919) and S. epidermidis (ATCC® 35984) targeting AI-2, lipase, bacterial attachment and biofilm formation, inhibiting sessile bacteria within a mature biofilm, eDNA production and promoting wound closure that contributes to the novelty of the current project.