Linking chemical phenotypes of different varieties of cannabis sativa to their antimicrobial activities against a range of microorganisms

Wardle, Joseph (2019) Linking chemical phenotypes of different varieties of cannabis sativa to their antimicrobial activities against a range of microorganisms. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Ethanolic, methanolic and water extracts of different chemical phenotypes of Cannabis sativa belonging to the Cannabaceae family were tested for their antimicrobial activity against two Gram negative species, seven Gram positive species and two fungal species using the Kirby-Bauer disc diffusion method. Successful extracts were tested for their minimum inhibitory concentration (MIC). All extracts tested proved ineffective against both Gram negative species and both fungal species. Gram positive organisms were inhibited by all extracts, to varying degrees, and produced MICs of under 10 μl of extract per ml of inoculated broth. The average zones of inhibition (ZOI) produced for the successful species, when all extract inhibitions were combined, varied from 12.52 mm for Enterococcus faecium to 21.08 mm for Streptococcus pyogenes. The CBG (cannabigerol) type Cannabis extract proved the largest ZOI producer with results averaging 21.62 mm when all species’ inhibition was combined, and CBCV (cannabichromavarin) proved to produce the smallest ZOIs against all species with only an average of 7.29 mm. Synthetic cannabinoids that act on the same CB1 and CB2 receptors in animals were also tested for their antimicrobial activity. Ten in total were tested with one, 5F – PB -22, producing very slight inhibition against all Gram positive species except MRSA, and two more (5f – NPB – 22 and STS – 135) producing very slight inhibition against MRSA but no other species. Bactericidal testing was performed on all successful extracts and the results indicated that nearly all cannabinoids, against all species, are bacteriostatic. However, these results are thought to not be accurate as the method used could result in potential false positive results that show bacteriostatic activity. The results obtained in this study were corroborated by some of the studies undertaken by other researchers, but also contradicted by others. In total the amount of studies for comparison is very small and the results they produce are contradictory. The data indicates that Cannabis sativa has antimicrobial activities but the differing results from the studies performed so far show that experimental variation between the studies may influence the species upon which the cannabinoids are successful.