Efficacy of photoactivated Myrciaria cauliflora extract against Staphylococcus aureus infection - A pilot study

Staphylococcus aureus is one of the major microorganisms that cause human diseases, leading from mild skin infections to serious diseases. With the use of semi-synthetic penicillins, methicillin-resistant strains called Methicillin-resistant Staphylococcus aureus (MRSA) have emerged, whose resistance pattern extends to other beta-lactam antibiotics. It has already been shown that photodynamic therapy is capable of inactivating MRSA as the laser excites the photosensitizer responsible for transferring its electrons to the molecular oxygen, generating extremely reactive molecules, such as singlet oxygen, being these reactive components the chemicals that promote the bacterial clearance. Thus, the research aiming at the development of new photosensitizers becomes important, especially to increase the amount of therapeutic resources available for the treatment of persistent infections related to this bacterium. In this context, Myrciaria cauliflora is a plant that has antimicrobial action and there are no reports of the use of its crude extract as a photosensitizer in antimicrobial photodynamic therapy. In that way, this work conveys an innovative way of the use of M. cauliflora extract as a photosensitizer, comprising its use as an antimicrobial agent when activated by light, against S. aureus. In vitro tests were performed where it was observed that after the photoactivation with blue LED light, the extract presented an augment in its antimicrobial activity, together with production of singlet oxygen. In the model of intradermal infection in Balb/c mice, a reduction in bacterial load was also detected, with raised expression of TNF-α, IL-17A, and MPO. Here, we demonstrate that the extract of M. cauliflora has photosensitizing action, promoting the production of singlet oxygen, besides IL-17A, TNF-α, and MPO.