Effect of Syzygium aromaticum and Rosmarinus officinalis extracts on Giardia lamblia and Streptococcus agalactiae isolated from Nile tilapia ( Oreochromis niloticus )

Two herbs (Syzygium aromaticum and Rosmarinus officinalis) were assessed for their antimicrobial activity against Giardia lamblia causing giardiasis in humans and Streptococcus agalactiae, a major fish pathogen causing streptococcosis. Each herb was extracted with 3 solvents: water, 95% ethanol, and methanol. Methanol extract from R. officinalis was strongly active against G. lamblia (IC50 = 0.689 mg/mL) and Syzygium aromaticum was good activity against G. lamblia (IC50 = 0.755 mg/mL). On the other hand, ethanol extract from Syzygium aromaticum was strongly active against G. lamblia (IC50 = 1.227 mg/mL) and R. officinalis was good active against G. lamblia (IC50 = 2.874 mg/mL). None of the aqueous extracts of the two plants were active against tested protozoan. Using swab paper disc assays, methanol extracts of Syzygium aromaticum and Rosmarinus officinalis produced the largest (22.2±1.2 mm) and (25.4±0.9 mm) inhibition zones, respectively. Determination of minimal inhibitory concentration (MIC) of herb extracts against S. agalactiae showed that the methanol extract of Rosmarinus officinalis had the lowest MIC value (6.25 mg/L). methanol extract of Syzygium aromaticum was a moderate MIC (12.5 mg/L). Such results indicate S. aromaticum methanol extract and ethanol extract from R. officinalis as possible candidates for further investigations to isolate and characterize their active principles as possible new natural anti-bacterial and anti-protozoal agents.