Broad-spectrum bactericidal synergy of silver-cannabichromene-cannabigerol triple combinations against healthcare-associated pathogens

AIMS: Healthcare-associated infections (HAIs) place a substantial burden on healthcare systems globally, with growing antimicrobial resistance (AMR) restricting treatment options, increasing patient mortality, and raising the cost of care. Silver is a broad-spectrum antimicrobial used widely to help control HAIs. However, its utility is limited by AMR and concentration-dependent cytotoxicity. To address these challenges, we systematically evaluated the antimicrobial amplification properties of nonintoxicating cannabinoids, naturally occurring molecules having a narrow spectrum of antimicrobial activity, aiming to increase the antimicrobial effect of silver against Gram-positive and Gram-negative HAI pathogens. METHODS AND RESULTS: Administered individually, silver and cannabinoid compounds cannabidiol (CBD), cannabichromene (CBC), cannabigerol (CBG), cannabidiolic acid (CBDA), cannabichromenic acid (CBCA), and cannabigerolic acid (CBGA) produced modest bacteriostatic effects on time-kill analysis. Pairwise silver-cannabinoid combinations were neither synergistic nor bactericidal consistently against both Escherichia coli and Pseudomonas aeruginosa. Triple combinations comprising silver (as silver sulfate or nanoparticles), CBC, and CBG were consistently synergistic and bactericidal against Staphylococcus aureus (MRSA), E. coli, and P. aeruginosa on time-kill analysis and achieved up to 64-fold lowering of silver minimum inhibitory concentration on checkerboard assay. Silver-CBC-CBG triple combinations further precluded the emergence of MRSA resistance on 20-day serial passaging, ameliorated the potential for cytotoxicity in fibroblasts and keratinocytes, and demonstrated significant clearing of biofilms formed by MRSA (P < 0.001) and P. aeruginosa (P < 0.001). CONCLUSIONS: The increased potency, broad-spectrum bactericidal action, and antibiofilm properties of these novel synergistic silver-CBC-CBG triple combinations may provide a useful solution for bacterial silver resistance and the control of HAI.