Group B Streptococcus Colonization Detection Culture

CPT Code(s):



Selective broth enrichment culture and aerobic bacterial culture


Monday - Friday




Specimen Requirements:

Type: Swab of vaginal and rectal specimen
Container/Tube: Sterile screw-cap container or stool transport (Para-Pak® white clean vial); no preservative
  • Other container types often leak or even explode during transport and may be rejected by the laboratory.

Sample Volume: Single or double bacterial swab in Amies agar gel transport or equivalent

Minimum Volume: Single bacterial swab in Amies agar gel transport or equivalent

Storage: Specimens should be kept at room tempeature.
Rejection Criteria:

  • Inappropriate specimen transport
  • Inappropriate transport conditions
  • Improper labeling
  • Specimen received after prolonged delay (more than 48 hours)
  • Cervical/endocervical, perianal, perirectal or perineal specimen, or any source other than vagina and rectum

Collection Procedure:

Collection of both a vaginal and rectal swab specimen is strongly recommended. Swab the lower vagina (vaginal introitus), followed by the rectum (i.e., insert a swab through the anal sphincter) using the same swab. Move the swab from side to side, or rotate the swab at the collection site, allowing for several seconds for the absorption of organisms by the swab. Cervical, perianal, perirectal or perineal specimens are not acceptable, and a speculum shouromterrld not be used for culture collection.

Reference Values:


Interpretation Data:



UFHPL Test #: 78075

Group B Streptococcus is currently one of the most significant human pathogens in the neonatal period. The most common mode of acquisition by the neonate is exposure to the maternal genital flora in utero through ruptured membranes or by contamination during passage through the birth canal. Infection is manifested in two major forms, early-onset septicemic infection manifest in the first few days of life and late-onset meningitis that occurs during the first few months of life. The Centers for Disease Control and Prevention (CDC) has recommended specific procedures for processing clinical specimens for culture of group B Streptococcus, which includes selective broth-enhanced culture followed by subculturing the broth to an appropriate agar plate for aerobic bacterial culture. Susceptibility testing is not routinely performed, as this organism is universally susceptible to penicillin; consequently, surveillance for resistance is not recommended.

The CDC and the American College of Obstetricians and Gynecologists (ACOG) recommend reflex susceptibility testing to clindamycin and erythromycin (D-zone test to detect inducible clindamycin resistance) for group B Streptococcus only for those patients at high risk for anaphylactic shock due to penicillin allergy.

For those patients without likely evidence of severe anaphylaxis, the CDC and ACOG recommend the use of cefazolin as the agent of choice for intrapartum chemoprophylaxis without the need for susceptibility testing. For those patients with group B Streptococcus that is resistant to clindamycin, the Centers for Disease Control and Prevention (CDC) and the American College of Obstetricians and Gynecologists (ACOG) recommend treatment with vancomycin without the need for additional susceptibility testing. Even though it is tested together with clindamycin in the D-zone test, erythromycin is no longer an acceptable alternative for intrapartum GBS prophylaxis for penicillin-allergic women at high risk for anaphylaxis, and susceptibility results for this agent will not be reported.


Reported Notes: