Pathogens are gradually becoming more resistant to conventional antibiotics as a consequence; the emergence of infectious diseases is becoming a serious threat to the public health. Thus, there is a need for new antibiotics with an alternative mode of action through novel chemical structure. Marine microorganisms are of considerable importance as new promising sources of a huge number of biologically active products than their terrestrial environment. Due to its distinctive features and rich biodiversity of the marine environment, Kurusadai Island was selected as a source for the isolation of bacteria with significant bioactivity. About 148 bacterial strains were isolated from different marine sediment of Kurusadai Island, Gulf of Mannar, India. Bacterial isolates were screened for their antimicrobial activity against some pathogenic microbes. Among the isolated marine bacteria, 9.6% were found to be antibiotic producers and their activity ranged from broad spectral to species-specific. A strain coded S2-27 was found to be highly potent in antimicrobial activity. Other experiments manifested that, S2-27 strain produces an extracellular substance that inhibited the growth of human pathogens like methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and other test pathogens. It has a significant activity to inhibit Gram-positive bacteria than Gram-negative pathogenic strains. Particularly, it exhibits significant activity against the fungal isolates such as Aspergillus niger, Aspergillus fumigates, Penicillum varians and Candida albicans. Based on phenotypical and genotypical characterization, the isolate S2-27 was identified as Bacillus licheniformis KKR. Therefore, the study revealed that marine bacteria represent a remarkable antimicrobial property.

Keywords: Kurusadai Island, sediment, extracellular substance, antimicrobial activity, B. licheniformis KKR.