Abstract
The search for antibiotic metabolites is increasing due to drug resistance been witnessed today. This study was conceived to isolate, identify and compare the antimicrobial metabolites yield of four actinomycetes isolated from Menengai crater soil, Kenya. The actinomycetes were isolated using starch casein, Luria Bertani (M1) and starch nitrate agar. The antimicrobial metabolites were extracted using standard techniques followed by purification, test for antagonism against selected pathogenic microbes, and cytotoxicity assay using Brine shrimp lethality test. Totally, 138 actinomycetes isolates were obtained from all the soil samples. Four isolates showed the highest potent potential against selected bacterial and fungal pathogens. The selected actinomycetes were coded; PAN 30, PAN 37, PAN 41, and PAN 154, and preserved at 4°C for further analysis. The difference in yield of the antimicrobial metabolites between liquid and solid-state fermentation was statistically significant (P= 0.005). Zones of inhibition did not vary significantly (F = 6.6046, P = 0.001338). The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC) of the antimicrobial metabolites extracted from PAN 30, PAN 37, PAN 41 and PAN 154 isolates were equal. The Half Lethal Concentration (LC50) in (µg/ ml) for the antimicrobial metabolites extracted from the 4 isolates were; PAN 30 (1.8168 ± 0.47), PAN 37 (3.4269 ± 0.56), PAN 41 (3.4269 ± 0.45), and PAN 154 (4.9397 ± 0.41). The four actinomycetes produced bioactive metabolites. Solid-state fermentation was superior to liquid-state fermentation in recovering the antimicrobial metabolites from the actinomycetes isolates. Molecular identification of the selected isolates needs to be carried out in a future study. Moreover, there is a need to determine the structure of the antimicrobials using nuclear magnetic resonance.
Highlights
Actinomycetes are a class of aerobic, spore forming, Gram positive bacteria
Their count ranged from 2 ± 0.3 - 9 ± 0.2 on starch casein agar (SC), Luria Bertani agar (M1) (5 ± 0.3 14 ± 0.3), and starch nitrate (SN) (4 ± 0.3 - 14 ± 0.2) (Table 1)
The current study demonstrated a significant difference in the amount of antimicrobials produced in liquid, and in solid-state fermentation of the isolates
Summary
Actinomycetes are a class of aerobic, spore forming, Gram positive bacteria. They belong to the order Actinomycetales (Khouloud and Ehab, 2015). Actinomycetes are one of the largest taxonomic units in the 18 major lineages within the bacterial domain (Gebreselema et al, 2014). They are the leading sources of antibiotics (Loganathan et al, 2014) but due to increased drug resistance, the need for novel drugs has gained a lot of prominence among researchers (Astalakshmi et al, 2014). Anwarul et al, (2016) added that synthetic drugs have more side effects when taken orally than those obtained from natural sources
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