Antimicrobial and antibiofilm effect of cannabinoids from Cannabis sativa against methicillin-resistant Staphylococcus aureus (MRSA) causing bovine mastitis.

Antimicrobial resistance (AMR) poses a serious threat to human, animal, and plant health on a global scale. Search and elimination techniques should be used to effectively counter the spread of methicillin-resistant Staphylococcus aureus (MRSA) infections. With only a few novel drugs in clinical development, the quest for plant-based alternatives to prevent the spread of antibiotic resistance among bacteria has accelerated. Treatment of MRSA infections is challenging owing to rapidly emerging resistance mechanisms coupled with their protective biofilms. In the present research, we examined the antibacterial properties of ten plant-derived ethanolic leaf extracts. The most effective ethanolic leaf extract against MRSA in decreasing order of zone of inhibition, Cannabis sativa L. > Syzygium cumini > Murraya koenigii > Eucalyptus sp. > while Aloe barbadensis, Azadirachta indica, had very little impact. Mangifera indica, Curcuma longa, Tinospora cordifolia, and Carica papaya did not exhibit inhibitory effects against MRSA; hence, Cannabis was selected for further experimental study. The minimal inhibitory concentration (MIC) of Cannabis sativa L. extract was 0.25 mg ml with 86% mortality. At a sub-MIC dosage of 0.125 mg ml, the biofilm formation was reduced by 71%. The two major cannabinoids detected were cannabidiol and delta-9-tetrahydrocannabinol (Δ9-THC), which were majorly attributed to substantial inhibitory action against MRSA. The time-kill kinetics demonstrated a bactericidal action at 4 MIC over an 8-20-h time window with a 90% reduction in growth rate. The results from SEM, and light microscopy Giemsa staining revealed a reduction in cells in the treated group with increased AKP activity, indicating bacterial cell membrane breakdown. These findings suggested cannabinoids may be a promising alternative to antibiotic therapy for bovine biofilm-associated MRSA.