The rapid recognition of Lancefield group B haemolytic streptococci

When grown overnight on Columbia agar in an atmosphere of hydrogen and carbon dioxide, haemolytic strains of Lancefield group B streptococci (Streptococcus agalactiae) produce orange or brown pigmented colonies. This production of pigmented colonies can be used for the rapid presumptive identification of these organisms as belonging to group B without the need for grouping by serological methods.