Assessment of Antimicrobial Activities and Toxicological Effects of Green and Red Cultivars of Roselle- Hibiscus sabdariffa L

Aims: The use of synthetic antibiotics has been the major way of curing diseases; however, over-use of antibiotics has led to emergence of multi-drug-resistant strains of several groups of microorganisms. This study aimed at examining roselle extracts for antimicrobial properties with a view to providing the best alternative to the injudicious use of synthetic antibiotics and also examines the toxicological effects of roselle extracts.

Methodology: Ethanolic and aqueous extracts of roselle leaves and calyces were evaluated for antimicrobial activity based on minimum inhibitory concentration (MIC50) using Broth dilution method. The toxicological effects based on LC50 were also evaluated using Brine shrimp- Artemia salina. Simple percentage was used to determine the mortality rate of the nauplii while the minimum inhibitory concentrations of the extracts were determined using MINITAB 17 statistical package (P<0.05). Data were expressed as mean ± standard deviation of three replicates.

Results: Roselle calyces, pre-flowering green and flowering red exhibited excellent inhibition to bacteria. Calyces had better antimicrobial activities and higher toxicological effects than the leaves. Green roselle at pre-flowering stage and red flowering were good for antimicrobial screening.

Conclusion: Roselle extracts possessed excellent antibacterial and antifungal properties. These can be explored to develop new drugs, which can suppress the resistant strains. All the plant extracts were greater than 1000 mg/mL, which indicates that they were non-toxic to brine shrimp larvae.