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.