## 3 Phytocannibinoids: Polyfunctional Molecules Promising to Develop Novel Antibiotics
### Antimicrobial Cannabinoids
although slightly less potent than CBD and CBG, showed antibacterial activity comparable to that of their corresponding natural products [83]. According to recent reports, 18 cannabinoids including CBC, CBD, CBG, CBN, \(\Delta^{9}\)-THC and their carboxylic precursors (pre-cannabinoids CBCA, CBDA, CBGA, \(\Delta^{9}\)-THCA), CBDV, THCV and their precursors (CBDVA, THCVA), \(\Delta^{8}\)-THC, CBL, 11-NCTHC, 11-HTHC and \(\Delta^{11}\)-THC were tested against MRSA USA300, a highly virulent and prevalent community-associated MRSA, by [PERSON] et al. [33]. Susceptibility tests were conducted according to the Clinical and Laboratory Standards Institute (CLSI) protocol [91]. CBG, CBD, CBN, CBCA, \(\Delta^{9}\)-THC, \(\Delta^{8}\)-THC, and \(\Delta^{11}\)-THC were potent antibiotics with MICs = 2 \(\mu\)g/mL. A moderate loss of potency was observed for their acidic precursors such as CBDA, CBGA and THCAA. THCV and CBDV were less active, displaying MICs = 4 and 8 \(\mu\)g/mL, respectively. It is well-known, that biofilm formation by MRSA, typically on necrotic tissues and medical devices, represents an important virulence factor influencing the persistence of MRSA and is typically associated with increased resistance to antimicrobial compounds. In this regard, [PERSON] et al. investigated also the capability of the above-mentioned cannabinoids to inhibit the formation of biofilms by MRSA [33]. According to the results reported, the tested cannabinoids except for varins, clearly repressed MRSA biofilm formation, with CBG exhibiting the most potent antib Biofilm activity. Indeed, at concentration of 0.5 \(\mu\)g/mL (1/4 MIC), CBG inhibited biofilm formation by \(\sim\)50% [33]. When its effect was evaluated on preformed biofilms by determining its minimal biofilm eradication concentration (MBEC), CBG eradicated preformed biofilms of MRSA USA300 at concentration of 4 \(\mu\)g/mL. Additionally, on MRSA persister cells, which are a nongrowing, dormant cells subpopulations, which exhibit high levels of tolerance to antibiotics, and are responsible of chronic and relapsing _S. aureus_ infections, such as osteomyelitisitis and endocarditis, the tested cannabinoids showed antipersisters activity which correlated with MIC values [33]. Again, CBG was the most potent cannabinoid against the persisters. In time-kill experiments, while the \(\beta\)-lactam oxacillin at 160 \(\mu\)g/mL (5 \(\times\) MIC) did not show any activity, CBG killed persisters in a concentration-dependent manner starting at 5 \(\mu\)g/mL, and rapidly eradicated a population of \(\sim\)10\({}^{8}\) CFU/mL MRSA persisters within 30 min of treatment. As expected, the two most common human metabolites of THC, (\(\pm\))11-NCTHC and (\(\pm\)) 11-HTHC, as well as CBL were inactive at the highest concentrations screened (MIC \(>\) 32 \(\mu\)g/mL). Unfortunately, in the study by [PERSON] et al., none of these analogous displayed bactericidal effects against _E. coli_[33; 78]. However, CBG was found to be effective also against Gram-negative bacteria when associated to polymyxin B or the less nephrotoxic polymyxin B nonapeptide [33; 78] and acted as a sensitizing agent in combination with various antibiotics [92]. Concerning the association with polymyxin B, it was proposed that polymyxins permeabilize the outer membrane of Gram-negative pathogens, unassailable by CBG, thus enabling CBG to reach and damage the inner membrane [33; 78]. Additionally, when _E. coli_ VCS257 was treated with CBD in combination with erythromycin, vancomycin, rifampicin, kanamycin or colistin, an enhanced antimicrobial effect was observed [92]. In the year 2020, [PERSON] et al., tested CBDA and CBD against _S. aureus_ and _S. epidermidis_ finding very low MIC for CBD (MIC = 1 \(\mu\)g/mL and 2 \(\mu\)g/mL, respectively), and MICs twice as high for CBDA, while CBDA displayed MIC = 4 \(\mu\)g/mL against MRSA USA300 [80]. In the same year, [PERSON] et. al. reported for CBD, MICs = 4, 4, 4, and 8 \(\mu\)g/mL against MRSA USA300, MRSE, _L. monocytogenes_ and _E. faecalis_ respectively [86].