A pinboard by
Dorcas Gado

PhD student, University of Pretoria, South Africa


Antimicrobial discovery

My research aim to evaluate plant secondary metabolites from South African plants in a bid to develop a safe and effective antibacterial agent with application in food-borne infection control. The world's population is estimated at 7.4 billion with Africa being the second most populated continent (15% of the worldb s population). About 600 million people globally suffer ill health due to consumption of contaminated foods of plant and animal origin, of which about 420 000 deaths are recorded each year (WHO, 2015). The World Health Organization further emphasizes that contaminated food creates a vicious cycle of diarrhoea and malnutrition, with the young, elderly and immunocompromised being the most vulnerable. Salmonella species are considered second only to Campylobacter as a major cause of gastrointestinal infections in companion animals, livestock and humans, particularly in developing countries. Handling and consumption of contaminated foods (meat, milk and eggs) are considered a major source of infection in humans. This public health risk reinforces the need for close monitoring and collaboration between public health and veterinary authorities to mitigate the risk at the human-animal interface necessary for health and food security. Gastroenteritis that is not self-limiting is mostly treated with a wide range of antibiotics. The indiscriminate use of these antibiotics has resulted in the upsurge of resistant and multi-resistant strains of bacteria. This complicates treatment, especially in patients with Human Immunodeficiency Virus (HIV), necessitating the search for novel, cheaper, safer and efficacious antibacterial products. Recent in vitro studies have revealed that indigenous South African plants possess antimicrobial properties against gastrointestinal disorders and diarrhoea-causing organisms. Hence this study intends to tap into the potentials of these plants for health advancement. This study aligns with national priority because it will directly serve the unreached communities with alternative medication while providing job opportunities for them. Potential bioactive compounds will be synthesized, a boost in agricultural potentials will be achieved through the reduction in Salmonella of animal origin and food security will be enhanced. Ultimately, the project will target poverty reduction through a combination of post-research application and extension services to reach the vulnerable and the poor.


Which tree orders in southern Africa have the highest antimicrobial activity and selectivity against bacterial and fungal pathogens of animals?

Abstract: The study randomly screened leaf extracts of several hundred southern African tree species against important microbial pathogens to determine which taxa have the highest activity and may yield useful products to treat infections in the animal health market.We determined the antibacterial and antifungal activity of 714 acetone leaf extracts of 537 different tree species against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Cryptococcus neoformans. A sensitive serial dilution microplate method was used.Several extracts had MICs as low as 0.02 mg/ml. We analysed 14 out of the 38 tree orders where we determined the activity of more than 8 different tree species representing 89% of all species examined. There were statistically significant differences in some cases. Celastrales, Rosales and Myrtales had the highest activity against Gram-positive bacteria, the Myrtales and Fabales against the Gram-negative bacteria and the Malvales and Proteales against the fungi. Species present in the Asterales followed by the Gentiales and Lamiales had the lowest activities against all the microorganisms tested. Fabales species had the highest activities against all the microorganisms tested. There was substantial selectivity in some orders. Proteales species had very high activity against the fungi but very low activity against the bacteria. The species in the Celastrales and Rosales had very low antifungal activity, low activity against Gram-negative bacteria and very high activity against Gram-positive bacteria.Against all classes of microorganisms, the four orders containing species with the highest average antimicrobial activities also contained several species with low activities against different pathogens and vice versa. These results therefore should be used with circumspection in selecting tree orders that would yield the highest probability of finding species with promising activities. Nevertheless there was a twofold increase in probability of finding extracts with interesting antifungal activity from orders with high mean activity than from orders with low mean activity. The probability increased to threefold and fivefold for Gram-positive and Gram-negative bacteria respectively.

Pub.: 29 Aug '14, Pinned: 27 Jul '17

Opportunities for natural products in 21(st) century antibiotic discovery.

Abstract: Natural products and their derivatives are mainstays of our antibiotic drugs, but they are increasingly in peril. The combination of widespread multidrug resistance in once susceptible bacterial pathogens, disenchantment with natural products as sources of new drugs, lack of success using synthetic compounds and target-based discovery methods, along with shifting economic and regulatory issues, conspire to move investment in research and development away from the antibiotics arena. The result is a growing crisis in antibiotic drug discovery that threatens modern medicine. 21(st) century natural product research is perfectly positioned to fill the antibiotic discovery gap and bring new drug candidates to the clinic. Innovations in genomics and techniques to explore new sources of antimicrobial chemical matter are revealing new chemistry. Increasing appreciation of the value of narrow-spectrum drugs and re-examination of once discarded chemical scaffolds coupled with synthetic biology methods to generate new compounds and improve yields offer new strategies to revitalize once moribund natural product programs. The increasing awareness that the combination of antibiotics with adjuvants, non-antibiotic compounds that overcome resistance and enhance drug activity, can rescue older chemical scaffolds, and concepts such as blocking pathogen virulence present orthogonal strategies to traditional antibiotics. In all these areas, natural products offer chemical matter, shaped by natural selection, that is privileged in this therapeutic area. Natural product research is poised to regain prominence in delivering new drugs to solve the antibiotic crisis.

Pub.: 02 Jun '17, Pinned: 27 Jul '17

Antibacterial activity of crude extracts of some South African medicinal plants against multidrug resistant etiological agents of diarrhoea.

Abstract: This study evaluated the antibacterial activity of some plants used in folklore medicine to treat diarrhoea in the Eastern Cape Province, South Africa.The acetone extracts of Acacia mearnsii De Wild., Aloe arborescens Mill., A. striata Haw., Cyathula uncinulata (Schrad.) Schinz, Eucomis autumnalis (Mill.) Chitt., E. comosa (Houtt.) Wehrh., Hermbstaedtia odorata (Burch. ex Moq.) T.Cooke, Hydnora africana Thunb, Hypoxis latifolia Wight, Pelargonium sidoides DC, Psidium guajava L and Schizocarphus nervosus (Burch.) van der Merwe were screened against Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, multi-resistant Salmonella enterica serovar Isangi, S. typhi, S. enterica serovar Typhimurium, Shigella flexneri type 1b and Sh. sonnei phase II. A qualitative phytochemical screening of the plants extracts was by thin layer chromatography. Plants extracts were screened for antibacterial activity using serial dilution microplate technique and bioautography.The TLC fingerprint indicated the presence of terpenoids and flavonoids in the herbs. Most of the tested organisms were sensitive to the crude acetone extracts with minimum inhibitory concentration (MIC) values ranging from 0.018-2.5 mg/mℓ. Extracts of A. striata, C. uncinulata, E. autumnalis and P. guajava were more active against enteropathogens. S. aureus and Sh. flexneri were the most sensitive isolates to the crude extracts but of significance is the antibacterial activity of A. arborescens and P. guajava against a confirmed extended spectrum betalactamase positive S. enterica serovar Typhimurium.The presence of bioactive compounds and the antibacterial activity of some of the selected herbs against multidrug resistant enteric agents corroborate assertions by traditional healers on their efficacies.

Pub.: 21 Jun '17, Pinned: 27 Jul '17