Comparison of two Methods used for Isolation of Antibiotic- producing Bacteria

Abstract

Research for antibiotics has been widely performed for about 50 years and new antibiotics are still being discovered to treat infectious diseases. This analytical study was conducted during the period from May to October 2012. The aim of this study was to evaluate methods of isolation of antibiotic-producer bacteria. Soil samples were collected from red sea and Kassala state. The samples were inoculated onto nutrient agar enriched with soil extract using the pour and spread plate methods. Bacterial colonies were counted in each method employing several serial dilutions, and the appropriate dilution of bacterial growth was chosen to detect antibiotic-producer bacteria by plate-over-lay method using bacterial clinical isolates and standard strains. Of the broad antibiotic producing bacteria, one isolate was chosen and evaluated against standard organisms and clinical isolates using cup plate diffusion method. From the result the isolation of antibiotic-producing bacteria revealed that the number of colonies forming units (cfu) /ml was high (50 cfu/ml) when Spread Plate Method was used compared with Pour Plate Method (29 cfu/ml).in dilution104 Moreover, the Pour Plate Method showed best growth distribution of colonies (16-21 colonies/plate) in dilution 10-5 while in Spread Plating method need more dilutions achieve the same distribution and number of colonies The result showed that the pour plate method was practically better than spread plate method. Yet, both methods were helpful and successful in isolation of various promising antibiotic producer bacteria from soil. This study concluded that the pour plate method was suitable and superior over the spread plate for isolation of antibiotic-producer bacteria from soil. The study also indicated that the Sudanese soils of various sources are rich with antibiotic producers. Further investigation is warranted to identify the producer, characterize the nature of inhibitor and validate the findings.