In vitro bioassay of antibacterial and antifungal activity studies of actinomycetes from soda lakes of Ethiopia

Abstract

The ever-increasing spectrum of microbial disease and emergence of life-threatening antibiotic-resistant pathogens necessitates more intensive search for microbial antagonistic agents from diverse symbionts and habitats. Based on these hypotheses the current study was initiated to investigate in vitro antibacterial and antifungal activities of both crude and pure compounds isolated from potential actinomycete isolates recovered from soda lakes of Ethiopia. Two soda lakes, Arenguade/Hora Hadho/ and Chitu were included in this study. A total of fifteen 12 water samples were collected and actinomycete cultures were isolated by serial dilution plating technique on various media. Morphological and biochemical characterization of selected isolates was done as described in the International Streptomyces Project Guidelines. Minimum inhibitory concentrations of the crude extract was determined for fungus using the protocol described in National Committee for Clinical Laboratory Standards and for the bacteria disc diffusion assay method as described in the Clinical and Laboratory Standards Institution. Ethanol extracts obtained from Solid State Fermentation a total of 36 isolates of actinomycetes were subjected to primary screening and tested for activity against the bacterial and fungal reference strain. Accordingly, the extracts from 10 isolates that were most active in the primary screen were 6 (16.66%) from Lake Chitu that were inhibited the growth of Gram-positive bacteria and fungal strain; 4 (11.11%) from Lake Arenguade that were inhibited Gram-negative bacteria and fungal. From evaluated the antibacterial and antifungal potential of two soda lakes water-derived actinomycetes; the best ones in terms of activity spectra were actinomycetes species isolated from Lake Chitu. Antibacterial and antifungal metabolite production was detected from isolates of Lake Chitu with maximum zone of inhibition within 5–6 days of incubation against Candida albicans ATCC 62376, Aspergillus niger, C. neoformans, F. oxysporum f. sp. melonis (CECT 20474), and Shigella boydii (clinical). All test microorganisms, except Staphylococcus aureus ATCC25923, E. coli ATCC 25922, and S. aureus (clinical isolate) were sensitive to the culture filtrate starting from 8–12 days of incubation. In terms of the effectiveness of the antibacterial activity, the antibacterial metabolite produced from different carbon sources were more effective on S. aureus (clinical isolate), A. niger, C. neoformans, S. aureus ATCC25923, Fusarium oxysporum f. sp. melonis (CECT 20474), Shigella boydii (clinical isolate) respectively. However, the most resistant test isolates with least activity was detected against Candida albicans ATCC 62376 and E. coli ATCC 25922.