One-Step Method Screens Pregnant Women for Streptococci B

A new one-step method that screens pregnant women for the presence of group B streptococci (GBS) produces positive results as early as 6 hours after inoculation.

The Strep B carrot broth kit, a unique modification of Granada broth, is used for the selective enrichment and identification of beta-hemolytic group B streptococci (Streptococcus agalactiae) from clinical specimens.

The production of orange, red, or brick red pigment is a unique characteristic of hemolytic GBS due to reaction with substrates such as starch, proteose peptone, serum, and folate pathway inhibitors. These components serve as the basis for culture media used to detect and identify these organisms.

A product of Hardy Diagnostics (Santa Maria, CA, USA), modification of the Granada broth (the separation of the supplements) increases the shelf life of the product and ensures well-defined and reliable pigment production in the presence of GBS. The advantage of this medium is that it is a single tube system that does not require subculturing to a blood agar plate, unless the results are negative.

Carrot broth was found to be more sensitive than the Lim broth and Granada agar plate methods, and even polymerase chain reaction (PCR). It is also reliable for the preservation of GBS should the physician request susceptibility testing at a later date.

A companion product for Strep B carrot broth assists in the isolation and identification of the nonhemolytic strains of GBS (which comprise 0.5% - 5.9% of the total GBS isolates.) The GBS Detect plate is used when subculturing the negative Strep B carrot broth cultures. It contains selective agents and hemolysis enhancers to cause nonhemolytic strains to appear hemolytic, so they can easily be recognized and identified within 24 hours.

Approximately 10-35% of women are asymptomatic carriers of group B streptococci (GBS) in the genital and gastrointestinal tracts. GBS remains a leading cause of serious illness and death in newborn populations, and therefore, the detection of GBS in the vaginal-anorectal area is critical to the prevention of neonatal GBS disease.

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