Antibiotics from Streptomyces spp. isolated from Namibian desert sand

The discovery of antibiotics has been one of the major breakthroughs in the history of medicine for the treatment of microbe-related infections. Soil-borne microorganisms have been known to potentially produce clinically important antibiotics. However, many studies have shown that most deadly disease-causing bacteria have acquired the ability to resist the actions of these antibiotics and this phenomenon is known as antibiotic resistance. The aim of the study was to discover antibiotics from sand collected from inside fairy circles in the Namib desert. The bacteria were isolated using the serial dilution method and pure cultures were made from a 1 X 10-4 plate. These bacteria were subjected to primary screening in which the bacteria resembling the Streptomyces morphological features were tested against non-Streptomyces bacteria (also isolated from the soil) and the four known pathogens (Escherichia coli, Staphylococcus aureus, Achromobacter xylosoxidans and Proteus vulgaris) for antagonistic activity. The Streptomyces resembling bacteria together with the bacteria that were susceptible were identified using the 16S rRNA sequencing method. Three bacteria were isolated and identified as Streptomyces parvulus strain R5-344, Kocuria turfanensis strain HO-9042 and uncultured Microbacterium sp. Clone 1c05. For the extraction and purification of the active compounds from the bacteria, a crude extract was made using ethyl acetate and spotted on TLC plates to separate the compounds. A direct TLC-bio-autography method was performed to show which compounds were antibacterial. The active section was scraped off from the TLC plate (Rf = 0.76) and extracted with ethyl acetate. The extract was analysed by 1H NMR and GC-MS for identification of the compounds. The comparison of the 1H NMR spectrum of the control and the active sample showed new peaks at chemical shifts of 4.33 ppm, 4.75 ppm and 0.90 ppm. And lastly, with the GC-MS analysis, three compounds were tentatively identified in the active fraction; one compound showed 92 % similarity to 2-methyloctacosane (Retention time (RT) = 16.420 minutes), the second compound showed 92 % similarity to acetic acid n-octadecyl ester (RT = 20.355 minutes) and the third one showed 87 % similarity to octacosyl acetate (RT = 22.185 minutes).Dissertation (MSc)--University of Pretoria, 2019.Plant Production and Soil ScienceMscUnrestricte