| dc.description.abstract | Diseases are the most dangerous enemy of man despite the many strides made in medicine today.
The growing list of antibiotic resistant human pathogens in recent years has made the search for
new, safe antibiotics a top priority in medical research. Actinomycetes were isolated from soil
using starch casein, Luria Bertani (M1) and starch nitrate agar media, supplemented with 25μg
ml−1 nystatin to minimize contamination with fungi and 10μg ml−1 nalidixic acid to minimize
growth of other bacterial species. The actinomycetes were screened for antagonistic activities
against Gram positive bacteria such as Staphylococcus aureus (ATCC 25923) and Enterococcus
faecalis (ATCC 29212), Gram negative bacteria, among them Escherichia coli (ATCC 25922)
and Pseudomonas aeruginosa (ATCC 27853) and pathogenic fungi which included Candida
albicans (ATCC 10231) and Alternaria citri (ATCC 1015) using primary and secondary
screening of the antibiotic metabolites. Four actinomycetes isolates coded PAN 25, PAN 41,
PAN 75 and PAN 110 were selected for further studies based on size of the zone of inhibition
and broad spectrum of activity against the test pathogens. The effect of composition of growth
media, aeration rate, incubation period and temperature, pH, inoculum concentration, carbon and
nitrogen sources and salt concentration on growth and production of antibiotics by the selected
antinomycetes was determined. The pure substances were subjected to Ultraviolet (UV) and
Fourier transform infrared (FT-IR) spectroscopy, liquid chromatography mass spectrometry (LCMS)
and nuclear magnetic resonance (NMR) test for structure elucidation. A total of 138
actinomycetes were isolated from the soils of Menengai crater out of which 20 inhibited growth
of the selected pathogenic microorganisms. Luria Bertani was the best culture medium for
optimization and production of antibiotic metabolites by the selected actinomycetes. The selected
actinomycetes grew optimally at pH 6, 28oC, 7 day incubation period, aeration at 200rpm, 1%
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inoculum concentration, grycerol as the carbon source, and oatmeal as the nitrogen source. The
optimum salinity for growth and production of the metabolites by the selected actinomycetes was
1.5%. The mean diameter of zone of inhibition of the test pathogens ranged from 26.40 ± 0.2mm
in PAN 25 to 37.60 ± 0.2 mm in PAN 75. The results on structural elucidation of the antibiotic
metabolites indicated that antibiotics from isolate PAN 25 was 2,3,4a,5,5a,6,12,12a-octahydro-
5-hydroxy-5-methyl-11a H-naphtho[2,3-g]chromene-4,11-dione which was novel, isolate PAN
41 (lasalocid acid), isolate PAN 75 (Ethyl 2-(4 – ethyl-1-methyl pyrrolidune-2-carboxamido) –
2-(tetrahydro-3,4,5-trihydroxy – 6-methoxy-2H – pyran – 2-yl) which was novel and isolate
PAN 110 (staurospine). This study established that soils from Menengai crater have many
actinomycetes some of which produce bioactive metabolites. The antibiotics inhibited growth of
Gram positive and Gram negative bacterial and fungal pathogens. | en_US |
