Evaluation of Some Extra-and Intracellular Cyanobacterial Extracts as Antimicrobial Agents

Increasing the microbial resistance to the current drugs is the one of the major problems nowadays. Therefore, there have been tremendous efforts towards finding new metabolites for the development of new antimicrobial drugs. Cyanobacteria were selected to investigate the antimicrobial activity against some pathogenic and toxigenic microorganisms. Water samples were collected from some water plants and different sites of River Nile during the period from December 2011 to August 2012. Many species of cyanobacteria were detected in the River Nile. Among them, three representative species were isolated and identified as Fischerella, Oscillatoria and Anabaena. Cyanobacterial mass, filtrates and organic extracts from each of it were examined for inhibitory activity against seven tested microorganisms; tow Gram-positive bacterium (Staphylococcus aureus ATCC 25923 and Bacillus cereus ATCC 33018 ) and three Gram-negative bacteria (Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 9027 and Salmonella typhimurium ATCC 14028) and two fungi included one strain as molds; Aspergillus niger nrrl 326 and one strain as yeast; Candida albicans ATCC 1023.The methanol extract showed more potent activity than hexane extract. The mehanolic extract from mass of Oscillatoria scored a high inhibitory effect against E. coli, Ps. aeruginosa, B. cereus and Sta. aureus. Generally, the broth microdilution assay gave minimum inhibitory concentrations (MIC) values ranging from 0.016 to 0.5 µl µl -1. The antibacterial activity of methanol extract from both cyanobacterial filtrate and mass was decreased or completely lost after boiling for 10,20,30 min or pasteurization at 800 C/15 min. On the other hand, the activity was stable or enhanced after previous heat treatments