In Bangladesh, algae have not been adequately explored for their potential as a source of bioactive substances. So, present work provides the eligibility of algae commonly found in Bangladesh as a prominent natural antibiotic against various pathogens. In vitro screening of organic solvent extracts (methanol, ethanol and chloroform) of ten fresh water and marine algae showed antimicrobial activity carried out by disc diffusion method against two gram positive, four gram negative bacteria and one fungus. Marine algal species performed better than fresh water algal species. Green algae are more potent than red and brown algae. Ethanolic extracts are more effective than methanolic and chloroform extracts. Ulva lactuca and Chlorella sp. revealed the best activity among other algal species in all solvent forms. Spirogyra crassa showed very poor antibacterial activity where its antifungal activity was moderate. Escherichia coli was more resistant bacteria in a comparison to others because it showed totally resistant against some algae. Highest zone of inhibition (26 mm) was recorded for chloroform extract of Ulva lactuca against E. coli where chloroform extract of Dictyopteris membranacea didn't show any microbial activity. At the end, it was clear that almost all extracts of all algal species revealed antimicrobial activity against all pathogens. These results give an indication of the presence of promising antimicrobial compounds in the algal species under studied. Further phytochemical studies are needed to elucidate these compounds structures and activity for use algae as an alternative natural antibiotic against synthetic conventional antibiotics.

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