Abstract

Cyanobacteria is a group of prokaryotic organisms that occurred originally in the world. Thailand is well known as an area of a high biological diversity. In our study, eighteen cyanobacteria from the natural area were isolated and screened for their antibacterial activities. Of these, two isolated cyanobacteria (NCI1 and NCI4) with positive antibacterial activities were identified by their morphology and 16S rRNA sequences as Phormidiumand Microcoleus group in family Oscillatoriaceae. The ethanol extracts of Phormidium sp. and Microcoleus sp. at various concentrations (0.2, 0.06, 0.03 and 0.015 g/ml) showed the antibacterial activity against Streptococcus enteritidis and Escherichia coli on the media. Each cyanobacterial extract showed more inhibition zones against S. enteritidisand E. coli by increasing their concentrations, especially those of Phormidium extracts. At the highest concentration 0.2 g/ml, the maximum diameter of inhibition were observed in the extracts of Phormidium sp. and  Microcoleus sp., 11 and 10 mm against S. enteritidis, and 10 and 10 mm against E. coli, respectively. As results, the extracts of Phormidium sp. and Microcoleus sp. showed potentially interesting antibacterial activities against the two pathogens. Therefore, the two cyanobacteria may be useful in various applications and used as basic knowledge for further investigations.

Key words: Phormidium sp., Microcoleus sp., antibacterial activity.