Antifungal Activities of Ocimum gratissimum L. Hydroethanolic Extract against Candida albicans ATCC 35659 and Toxicity Analysis on Oreochromis niloticus Larvae

Abstract

Background The use of plant extracts as a sustainable substitute for antimicrobials in aquaculture is constrained by a poor understanding of their potential toxicity to aquatic organisms. This study aimed to investigate the antifungal activity of the hydroethanolic extract of Ocimum gratissimum leaves against Candida albicans ATCC 35659 while assessing its toxicity on Nile tilapia larvae. Methods The study included control bacterial germs, Staphylococcus aureus ATCC 29213 and Escherichia coli ATCC 25922. In vitro, growth toxicity on the yeast was evaluated using concentrations (50–500 mg/mL) of the plant extract in standard culture media. Nystatin was used as a control at 250 mg/mL. Subsequently, the toxicity of the extract was analysed using four serial two geometrical fold dilutions (0, 250–2000 mg/L) in a randomized duplicated trial with 20 fish larvae per treatment. The survival of the fish was monitored for up to 96 hours. Results Our findings showed that the extract did not have a bactericidal effect, but it exhibited significant differences in the inhibitory zones against the targeted Candida albicans. The extract showed an exhibitory zone of 35.51 ± 6.12 mm (500 mg/mL) and 20.45 ± 3.89 mm (250 mg/mL), while Nystatin had 33.53 ± 2.23 mm (Df2.9, F: 19.03, p: 0.001). However, subjecting the fish to immersion in the extract at a concentration above 500 mg/mL resulted in a high mortality rate of 100%, indicating the potential occurrence of detrimental effects on aquatic fauna. Conclusion These findings underline the need for a comprehensive understanding of the potential toxicity of plant extracts to aquatic organisms when considering their use as sustainable alternatives in aquaculture. Future research should focus on elucidating the mechanisms of toxicity and identifying optimal concentrations that balance antifungal efficacy with minimal damage to aquatic life.