Abstract
In search for bioactive compounds, 88 fungal isolates were collected from three Egyptian marine habitats. Crude extracts of 17 marine derived fungal isolates out of the 88 isolates showed variable activity against some human pathogenic bacterial strains (Salmonella enterica, Proteus sp., Klebseilla pneumonia, Staphylococcus aureus and Escherichia coli). The most potent fungal isolate that showed the highest antimicrobial activity was molecularly identified as Aspergillus welwetsichiae. Optimization of culture conditions of A. welwetsichiae revealed that the highest antimicrobial activity was obtained in shaking conditions (150rpm), using Czapek- dox medium, at pH 9 and incubation at 25°C for 3 days. Salmonella enterica was the most sensitive test organism regarding the highest inhibition zone through all the optimization tests. Ethyl acetate extract of A. welwetsichiae was subjected to chemical analysis and declared that the active antibacterial metabolite is a mixture of acid (Mono (2-ethylhexyl) phthalate) and ester (bis (2-ethylhexyl) phthalate). Retesting the two compounds separately, they showed no activity which confirmed the synergistic antibacterial effect of the two compounds together. Upon testing the cytotoxic effect of the active antibacterial metabolite (mixture of acid and ester) against human lung fibroblast normal cell (WI-38 cell line), the results showed that there was a very weak inhibitory activity suggesting the possibility of considering it as a safe compound for further steps as a pharmaceutical product.

Key words: Marine derived fungi, Antimicrobial compounds, Aspergillus