ABSTRACT

This study was to evaluate the isolation of soil bacteria for potential production of antibiotics and their inhibitory activity against some pathogens. In the screening of 15 soil samples for antibiotic producing organisms, a total of 36 bacterial species were isolated using the spread plate technique. The bacterial isolates identified using morphological and biochemical characterization included Bacillus species, Enterobacter species, Micrococcus specie and Pseudomonas aeruginosa. Bacillus species was the most frequently isolated organism as it has the highest percentage of occurrence of 15(42.8%), then followed by Enterobacter species and Micrococcus specie with the percentage occurrence of 8(22.8%) and finally Pseudomonas aeruginosa with the percentage occurrence of 5(14.3%). The various isolates were tested against strains of E. coli, Staphylococcus aureus and Salmonella typhi using the paper disc diffusion technique. However, the results showed that Gram positive bacteria and Gram negative bacteria had equal occurrence, The most prevalent isolate was Bacillus spp. The results of antibiotic sensitivity testing of the various bacteria isolate revealed that the isolate Enterobacter aerogenes had no significant inhibitory effect on Escherichia coli and Staphylococcus aureus but showed an inhibitory effect on Salmonella typhi with a zone oflnhibition of 11.0mm. The test organisms Escherichia coli, Staphylococcus aureus and Salmonella typhi had the highest sensitivity (14mm, 13mm and 17mm respectively), against the isolates(Micrococcus species, Pseudomonas aeruginosa and Bacillus megaterium). The standard antibiotics (Gentamicin), was used as control inhibiting the test bacteria respectively; it had higher inhibitory activity compared to the test isolates. Therefore, the results clearly unmasked antibiotic producing microorganisms from the soil samples and identified Bacillus spp as having high inhibitory effect on the test organisms.