ABSTRACT

Antibiotic is one of the most important commercially exploited secondary metabolites produced by bacteria, fungi and Streptomyces and employed in a wide range. Most of the antibiotics used today are from the microbes. The aim of the study is to screen microorganisms isolated from different dumpsites in Umuahia, Metropolis for antibiotic production. A total of fifteen (15) waste dump soil samples were collected randomly from three (3) different waste dumpsites which includes about 2cm depth of the soil samples were taken with the aid of soil auger into a sterile plastic container and was transported to the laboratory for microbiology analysis. Serial dilution technique was employed in the inoculation of the soil samples. Each of the samples was diluted in the 10-fold serial dilution technique. Six test tubes were set up in a rack and filled with 9ml of sterile distilled water labelled stock, 10-1, 10-2, 10-3, 10-4, 10-5 and 10-6 respectively. One gram of each soil sample was added to the tube labelled stock and properly mixed together. An Aliquot (1ml) was transferred from this tube into the one labelled 10-1 and carefully mixed. Similarly, 1ml was drawn up from the 10-1 tube and transferred to the 10-2 tube. This was continued up to the last tube labelled 10-6 from where 1ml was discarded. Dilutions from 10-3, 10-5 and 10-6 were inoculated onto freshly Nutrient agar and Sabouraud Dextrose Agar Plates. The Spread plate method of inoculation  was used where 0.1ml of the respective dilutions(10-3 10-5 and 10-6) were plated on various agar plates and evenly spread over the entire plate using a flame sterilized glass rod. The inoculated plates were incubated at 350C for 24hrs for bacteria and at room temperature (25±20C) for fungi. A total of 45 bacterial and 19 fungal isolates were obtained from the soil samples. Antibiotic activity screening using the agar well diffusion was used to evaluate the inhibitory activity of  isolates against bacteria strains including Staphylococcus aureus, Salmonella typhi, Escherichia coli. Of the 64 isolates, (4/64) were active against at least one of the test organisms with diameter zones of inhibition ranging from 10.0mm to 17.0mm. Isolate AUG7 exhibited the strongest antibacterial activity against S. typhi and E. coli with diameter zones of clearing of 17mm and 11.0mm respectively followed by AUG29 which recorded a zone of inhibition of 14mm and 10mm against E. coli and S. aureus, respectively. AUG7 was tentatively identified as an Enterobacter species based on their colonial morphology and biochemical tests results. Among the isolates which demonstrated antagonism against the test bacteria, AUG18, AUG26, and AUG7 were identified as Bacillus spp., Penicillium spp and Enterobacter species respectively. In conclusion, search of new antibiotics, relatively simple and rapid methods have been developed for screening microorganisms for antibiotic producing ability. Soil samples are commonly employed in the isolation of antibiotic producing organism. The  detection  of  these  antagonistic  substances  revealed interesting properties that justify its importance and its study on the potential  application  in  biological  control  of  pathogenic microorganisms and spoilage  food. For these reasons, the biochemical nature and the best conditions to production  of the substances  studied  in  this  work  are  being  investigated  to  further purification experiments.