BIO-PROSPECTING FOR BROAD SPECTRUM ANTIBIOTIC PRODUCING ACTINOMYCETES ISOLATED FROM VIRGIN SOILS IN KERICHO COUNTY

Abstract

Antimicrobial drug resistance is a rising concern in the treatment of infectious diseases and necessitates the need for discovery of novel, potent antimicrobial compounds. Since the natural environment remains a potential source of novel antimicrobial products, this study was performed to test the potential of soils from Kericho County for antibiotic-producing Actinomycetes. Soil samples (214) were randomly collected from virgin soils of Kipkelion East, Kipkelion West, Belgut, Ainamoi, Sigowet and Bureti sub-counties in Kericho County from a depth of between 11cm-16cm from the surface of the soil profile. The Actinomycetes were isolated using serial dilution and antimicrobial activity screening done using modified agar disc diffusion method. DNA was then extracted from the isolates that showed activity and the 16S rRNA gene amplified using primers specific for Actinomycetes. The amplified gene was sequenced and phylogeny analysis done. A total of 107 Actinomycetes were isolated and from these only 39 (36.4%) showed antimicrobial activity against five of the six test isolates. These included reference strains Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922) and Candida albicans (ATCC 90028) and three clinical strains Trichophyton mentagrophyte, Microsporum gypseum and Methicillin Resistant Staphylococcus aureus (MRSA). Two of the isolates showed activity against MRSA and four isolates showed a higher potency than the standard drug Chloramphenicol (30μg/disc) against S. aureus. Most of the isolates 84.6% also showed good antimicrobial activity against T. mentagrophyte though significantly lower than the control drug Itraconazole (2 μg/ml). The 16S rRNA gene was amplified in only 15 isolates. Sequencing showed that 93.3% were of the genus Streptomyces while 6.7% were of the genus Rhodococcus. From the results, the soils from this region harbour Actinomycetes which may have good potential of producing novel antibiotics against gram positive bacteria and dermatophytes. The metabolites from the isolates that showed good activity should be extracted and purified and their components analysed and compared to the drugs in the market to find out whether there are any novel compounds.