Screening and Characterization of Bioactive Actinomycetes and Their Products From Nepal Against Multidrug Resistant Bacteria and Fungi
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Department of Microbiology
Abstract
Actinomycetes are versatile producers of diverse secondary metabolites
including antibiotics. New therapeutics of microbial origin is essential to combat
multidrug resistant human pathogens. This descriptive study was conducted to
isolate, screen and characterize bioactive actinomycetes and their anti-microbial product
along with optimization of cultural conditions for better metabolite production. A total of
240 soil and 48 water samples were collected from different parts of Nepal and
actinomycetes were selectively isolated, primarily screened by perpendicular
streak method and secondary screening was performed by agar well diffusion
technique against selected bacteria and fungi. The minimum inhibitory
concentration of ethyl acetate extract was carried out by tube dilution method.
The screened actinomycetes strains were characterized by cultural,
morphological, biochemical and 16SrRNA sequencing. Optimization of
fermentation was carried out by cultivating the screened strains separately at
different nutritional and cultural conditions. Characterization of ethyl acetate
extract was performed by FT IR and LC-MS method.
Out of 320 actinomycetes isolates, 120 (37.5%) were found bioactive against one
or more test microbes. Among them only 4(3.3%) were inhibitory against all test
organisms. In secondary screening, the most potent strain A3
showed highest
activity against C. albicans with zone of inhibition of 41.33± 1.5mm and lowest
minimum inhibitory concentration of 2.5mg/ml against C. albicans and E. coli.
Phenotypic characteristics predicted that strains A
3,
D
2
, P
4
and J
1
were
Nocardiosis prasina, Streptomyces violarus, S. krainskii and S. tsusimaensis
respectively and the most potent strain A
3
was genotypically characterized as N.
prasina. Optimization study revealed that starch, casein and potassium nitrate
supported maximum bio mass and metabolite production in A
3
, P
4
and J
1
strains.
Likewise, incubation temperature of 30
v
0
with pH 7-8 for 7-8days incubation time
were found optimum for all screened strains. FT-IR and LC-MS analysis
revealed that the ethyl acetate extracts of all the strains contained diverse
functional groups and compounds having molecular mass (m/z) ranging from
106 to 986.
Key words: Antibiotics, Multidrug Resistant, FT-IR, LC-MS, Actinomycetes.