Antimicrobial profile of extremophiles from aqua to terrestrial habitats

The emergence of antibiotic resistance among pathogenic and commensal bacteria has become a serious problem worldwide. Use and overuse of antibiotics in a number of settings are contributing to the development of antibiotic-resistant microorganisms (1). Recently, the rate of discovery of new compounds from existing genera obtained from terrestrial sources has decreased, while the rate of re-isolation of known compounds has increased. Moreover, rise in the number of drug-resistant pathogens and limited success of strategies such as combinatorial chemistry in providing new agents indicates an uncertain forecast for future antimicrobial therapy (2, 3). Thus, it is critical that new groups of microbes from unexplored habitats be pursued as sources of novel antibiotics and other small-molecule therapeutic agents(4). In the present study 36 bacterial and 24 fungal isolates from different aqua to terrestrial sources were grown in broth culture for production of metabolites. The intracellular metabolites were extracted with methanol and extracellular metabolites were extracted with ethyl acetate. The crude intra and extracellular extracts were evaluated for antimicrobial activity by agar diffusion method using various bacterial and fungal test organisms. Ciprofloxacin (100 μg/ml) was used as standard for antibacterial studies and Nystatin disc (10 μg/disc) was used for antifungal studies. It was found that the isolate UG-3 (extracellular extract) showed both antibacterial and antifungal activity against all the test organisms employed. UG-6 was also equally promising, except that E.coli was resistant to the extracellular extract of UG-6. Intracellular extracts of MC-1, E-1, LS-4 , PSA-2 and extracellular extracts of M-4. LS-3F, GS-4, VHSS-2, LS-3XY, VHSP-5, PSA-3 were found to be active against all test organisms except Candida albicans. Extracellular extract of GS-1 and intracellular extracts of G-1, G-5, and K2A were found to be active against all test bacteria employed.