The antimicrobial investigation of indigenous South African medicinal plants against oral pathogens
Oral diseases in South Africa remain a huge public health problem due to the high cost, prevalence, severity and the influence on the patients well-being. Treatment for oral diseases requires the need for specialist dental health care workers and come at a high cost causing a great burden on the health system. The three most important oral diseases are dental caries, caused by Streptoccocus mutans, Streptococcus sanguis, Lactobacillus acidophilus and Lactobacillus casei, periodontal diseases caused by Porphrymonas gingivalis and Fusobacterium nucleatum and oral candidiasis caused by Candida albicans, Candida glabrata and Candida krusei. An ethnobotanical review has revealed that over a 120 South African medicinal plants are used for the treatment of oral diseases. This coupled with the lack of research on the subject, allowed for the investigation of the antimicrobial efficacy of some South African plants against oral pathogens. A total of 140 aqueous and organic extracts and six essential oils were prepared from 31 different plant species. These plant samples were screened for antimicrobial efficacy against nine oral pathogens using the micro-titre plate dilution assay. Plant extracts that were found to have noteworthy antimicrobial activity against Streptococcus mutans were further evaluated on the effect on S. mutans biofilm formation using the glass slide method. The toxicity profiles of plant samples that were found to have noteworthy antimicrobial activity were evaluated using the brine shrimp lethality assay. The plants did not exhibit antimicrobial efficacy against all nine pathogens in this study, instead, most were very specific to disease conditions. Some plants did show good antimicrobial activity against four of the nine pathogens tested (A. afra leaves, C. torulosa stems, C, brachiata leaves and H. natalensis leaves).The organic extract of Cissampelos torulosa stems displayed the lowest MIC value of 0.05 mg/ml against both Lactobacillus spp. This antimicrobial activity was also observed with the organic extract of Spirostachys africana leaves against Candida albicans. In some instances, a direct relationship was found between the traditional use of the plant and the antimicrobial activity observed. For example, noteworthy activity (MIC < 1.00 m/ml) was observed against all three Candida spp. for Clematis brachiata (leaves), a plant traditionally used to treat oral thrush. Englerophytum vi magalismonatanum (stems) displayed notable activity against both Streptococcus spp. (MIC 0.83 mg/ml against S. mutans and MIC 0.67 mg/ml against S. sanguis). Spirostachys africana leaves displayed the greatest anti-adherent properties against S. mutans biofilm formation at both 24 and 48 h, reducing the biofilm by 97.56% and 86.58% respectively. The majority of plant samples tested in the brine shrimp lethality assay (BSLA) were considered safe, however, 13 plant samples were considered toxic, at a concentration of 1 mg/ml, and their LC50 values were determined. The findings from the results favour the potential use of these plants in treating oral diseases such as dental caries, periodontal diseases and oral thrush, and scientifically validates the traditional use of some of these plants.
A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the degree of Master of Pharmacy, Johannesburg, 2017