Islam’s Medium Base for Group B Streptococci

Principle And Interpretation

Islam (1) formulated this medium to exploit the ability of most Group B Streptococci to produce orange/red-pigmented colonies when incubated under anaerobic conditions. Lancefield first noted carotenoid pigmentation, characteristic of group B Streptococci when incubated under anaerobic conditions (2). This medium also supports growth of other genital bacteria that cause neonatal infection (1) such as anaerobic Streptococcus, Bacteroides and Clostridium species. Proteose peptone provides the necessary nutrients for the growth of Group B Streptococci. Disodium and monosodium phosphates provide buffering to the medium. Pigmentation can be enhanced by adding trimethoprim / sulphonamides (3). No inhibition of growth occurs and the pigmentation is seen clearly over a radius of 10-20 mm. The medium must have the correct pH to ensure good pigmentation but some strains of Group B Streptococci do not produce pigmented colonies (4). Other organisms that can grow on this medium do not produce the characteristic orange-red pigment. Inoculate the specimen swab onto the surface of Islams Medium. If desired, apply a disc containing 300 or 500µg of sulphafurazole onto an area of the plate where growth can be expected to be moderately profuse. Incubate the plates anaerobically at 35°C for 24 to 48 hours.