Secondary screening test
The active isolates resulted from primary screening; promising isolates were tested for their extra cellular antibiotic production capabilities under submerged fermentation conditions. The production medium containing Soyabean meal 1%, glucose 1%, NaCl 1% and CaCO3 0.1% was used for antibiotic production employing isolates obtained from marine sediments of Andaman and Nicobar islands well sporulated, 7 day old slants of the selected isolates were used for the antibiotic production studies. Sterile water was added to each slant and spore suspension was prepared. 5 ml of this spore suspension was added to 45 ml of the respective production media and incubated at 28°C on a rotary shaker (120 rpm) for 4 days. Then samples were collected in to sterile centrifuge tubes and centrifuged at 3000 rpm for 15 min; the clear supernatant was used for antibiotic assay using agar diffusion method (Barry and Thornsberry, 1985), employing nutrient agar for bacteria and potato dextrose agar for fungi. The activity of 50 μl of spent medium of all above isolates was compared with the activity of standard antibiotics like 100 μg/ml of each streptomycin and tetracycline for bacteria, flucanozole and greseofulvin (methanol extract) for fungi. The test organisms mentioned in primary screening were also used in secondary screening test.