Comparative study of the antibiotic producing potentials of three freshwater Actinomycetes belonging to the Saccharopolyspora and Actinosynnema genera.

Abstract

Crude extracts of three actinomycetes species belonging to Saccharopolyspora (TR 046 and TR 039) and Actinosynnema (TR 024) genera were screened for antibacterial activities against a panel of several bacterial strains. The extracts showed antibacterial activities against both Gram-negative and Gram-positive test bacteria with inhibition zones ranging from 8 to 28 mm for extract obtained from TR 046; 8 and 15 mm for extract obtained from TR 039 and 10 to 13 mm for extract obtained from TR 024. The minimum inhibitory concentrations ranged from 0.078 to 10 mgml-1 for extract obtained from TR 046; 5 and >10 mgml-1 for extract obtained from TR 039 and 1.25 and 5 mgml-1 for extract obtained from TR 024. The bactericidal activity of extract obtained from TR 046 was evaluated against 5 test bacteria with different susceptibilities to the extract by time-kill assay. The extract showed strong bactericidal activity against Bacillus pumilus (ATCC14884) reducing the bacterial load by 104 cfuml-1 and 102 cfuml-1 at 4 × MIC and 2 × MIC respectively after 6 hr of exposure. It also showed good bactericidal activity against Proteus vulgaris (CSIR 0030) achieving a 0.9log10 and 0.13log10 cfuml-1 reduction at 5 mgml-1 (4 × MIC) and 1.25 mgml-1 (2 × MIC) respectively after 12 hr of exposure. The extract was however weakly bactericidal against two environmental bacterial strains Klebsiella pneumoniae and Staphylococcus epidermidis, and against Pseudomonas aeruginosa (ATCC 19582), the extract showed bacteriostatic activity across all MIC ranges used. The test actinomycetes appear to have immense potential as a source of new antibacterial compound(s).