In vitro time-kill studies of antibacterial agents from putative marine Streptomyces species isolated from the Nahoon beach, South Africa

We assessed the antibiotic production potentials of ten putative Streptomyces strains isolated from the Nahoon beach and their antibacterial activities against a wide range of bacteria including reference strains, environmental strains and clinical isolates. The minimum inhibitory concentrations (MICs) of the crude ethyl acetate extracts ranged from 0.039 to 10 mg/mL and the least minimum bactericidal concentration (MBC) demonstrated was 0.625 mg/mL against a reference strain Staphylococcus aureus ATCC 6538. Time kill kinetics of all extracts revealed bacteriostatic and bactericidal activities. Average log reductions in viable cell counts for all the extracts ranged from 0.86 log₁₀ and 3.99 log₁₀ cfu/mL after 3 h interaction and 0.01 log₁₀ and 4.86 log₁₀ after 6 h interaction at MIC, 2 × MIC, 3 × MIC and 4 × MIC concentrations. Most of the extracts were speedily bactericidal at 3 × MIC and 4 × MIC resulting in over 50% elimination of most of the test bacteria within 3 and 6 h interaction. Our findings suggest that the marine Streptomyces isolated from the Nahoon beach have tremendous potential as sources of new antibacterial compounds.