Purpose: To investigate the antimicrobial activity of crude and fractionated extracts of Biemna tubulosa and Stylissa spp. thriving in Trou aux Biches lagoon, North East Mauritius.

Methods: Crude extracts (methanol: dichloromethane 1:1) and fractions of Biemna tubulosa and Stylissa spp  (hexane, ethyl acetate and butanol) were tested against some bacterial organisms, namely, Escherichia coli, Staphylococcus aureus and Enterococcus faecalis, using broth microdilution assay. The extracts were screened for the presence of compounds that could be responsible for bioactivity.

Results: Preliminary chemical screening revealed the presence of tannins, saponins, terpenes, alkaloids and phenols. The hexane fraction of Stylissa spp. and the ethyl actetate and butanol extracts of Biemna tubulosa were more active than the control antibiotic. Maximum antimicrobial activity was noted for the butanol fraction of Biemna tubulosa with minimum inhibitory concentration (MIC) of 0.091 mg/ml against E. coli.  The hexane soluble fraction of Stylissa spp. was more active with MIC of 0.125 mg/ml against S. aureus and E. coli and 0.250 mg/ml against E. faecalis.

Conclusion: The broad spectrum antibacterial activity of these sponges seemed to be due to the presence of sesterterpenes and triterpenes, alkaloids and tannins detected in the extract fractions. This is probably the first report on the antimicrobial activity of Biemna tubulosa and Stylissa spp. from Mauritius waters.