The anti-biofilm activity of cannabinoids against methicillin-resistant Staphylococcus aureus.

Aims: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital-acquired pneumonia with resistance against beta-lactam antibiotics. New, potent antibiotics against MRSA with other mechanisms of action are thus urgently needed. Recently, cannabinoids have been evaluated for antimicrobial activity in the ongoing search for new anti-infective agents, but their anti-biofilm effect has not been extensively studied. In this study, five main phytocannabinoids-cannabidiol (CBD), delta-9-tetrahydrocannabinol (THC), cannabinol (CBN), cannabigerol (CBG), and cannabichromene (CBC) were examined for their activity against MRSA biofilms.

Methods and results: The anti-biofilm activity was assessed by crystal violet staining, resazurin metabolic assay, reactive oxygen species (ROS) assay, and propidium iodide membrane integrity test. The minimum inhibitory concentrations of all tested cannabinoids were between 1 and 2 µg/mL. CBN showed the most potent anti-MRSA biofilm activity, significantly reducing biofilm biomass and bacterial viability. It also induced the highest intracellular ROS levels. In contrast, CBD was the least effective among the tested cannabinoids in most of the anti-biofilm assays, yet it caused the greatest membrane damage to bacteria within the biofilm.

Conclusions: This study showed that despite being chemically similar, the cannabinoids demonstrated different potency and potentially different mechanisms of action against MRSA. More research is needed to investigate how they act on this pathogen and its biofilm.