Isolation and characterisation of antibiotic producing microorganisms in composted Nigerian soil

Compost samples obtained from different locations within the premises of the university of Lagos were analysed to determine the presence and types of antibiotic-producing bacteria, fungi and actinomycetes using nutrient agar, potato Dextrose agar and starch casein nitrate agar respectively as culture media. A variety of bacteria were isolated and these included Staphylococcus aureus, B. subtilis, B. pumilis, B. lactesporus, B. megaterium, B. pulvifaciens, B. licheniformis, Streptococus spp., Corynebacterium spp. and E. coli. The fungal isolates encountered were Aspergillus niger, A. flarus, T. viridae, P. chrysogenum, P. pinofylum and Absida spp., while the following actinomycetes were identified: Norcadia spp., Micromonospora spp., Streptomyces scabies, S. reticuli and S. hygroscopicus. When these organisms were screened for antibiosis, the following species were found to be antibiotic producers: B. licheniformis, B. subtilis, Penicillium chrysogenum, Streptomyces reticuli, S. hygroscopicus and Micromonospora spp. The fungus Penicillium chrysogenum had the highest rate of antibiotic production with an inhibitory zone width of 17mm while Trichoderma viridae produced toxins lytic to other fungal hyphae.