Standard laboratory procedures

Test your knowledge on standard laboratory procedures related to GBS detection

According to the American Society for Microbiology (ASM) Guidelines for the Detection and Identification of Group B Streptococcus

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ASM Guidelines

question 1

Why is selective enrichment broth recommended vs. non-selective enrichment broth?

Selective enrichment broth incubation is reported to increase GBS detection compared to non-selective broths resulting in up to 2.5-fold increased frequency of GBS-positive screening

Selective broths include components to promote the growth of enteric organisms

Selective broths include components to promote the growth of some Gram positive bacteria such as Staphylococcus

Source: CDC

All of the above

Correct!

A is correct: According to the ASM guidelines, “Selective enrichment broth incubation is reported to increase GBS detection compared to non-selective broths resulting in up to 2.5-fold increased frequency of GBS-positive screening.* Selective broths include components to inhibit or suppress the growth of enteric organisms and some Gram positive bacteria such as Staphylococcus. When non-selective broth is used, these organisms can overgrow GBS making detection difficult.”

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*Citations can be found in the ASM guidelines

question 2

True or False The use of selective enrichment broth without blood is acceptable.

TRUE

False

Correct!

True is correct: According to the ASM guidelines, “Acceptable selective enrichment broths include: Todd-Hewitt broth with gentamicin (8 μg/ml) and nalidixic acid (15 μg/ml) (known as Trans-Vag Broth), Todd-Hewitt broth with colistin (10 μg/ml) and nalidixic acid (15 μg/ml) (known as Lim broth).* Modified formulations of these selective media are available from commercial vendors and are generally acceptable. The addition of 5% defibrinated sheep’s blood to Trans-Vag Broth was shown to enhance detection of GBS.* However, evidence supporting supplementation of selective enrichment broth to improve GBS detection is limited. Therefore, use of selective enrichment broth without blood is acceptable.”

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*Citations can be found in the ASM guidelines

40/100

question 3

Which of the following is NOT true?

Infrequently, the growth of other microorganisms found in vaginal-rectal samples may decrease recovery of GBS after enrichment broth incubation.

Laboratories may choose to directly inoculate agar culture plates in addition to enrichment broth inoculation.

Laboratories may choose to do direct specimen plating alone without enrichment broth culture.

When positive, direct plating decreases time-to-detection of GBS compared to enrichment broth incubation followed by plating to agar media.

Correct!

C is correct: According to the ASM guidelines, “…direct specimen plating alone, in the absence of enrichment broth culture, is unacceptable and should not be performed.”

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question 4

True or False GBS is comprised of only hemolytic strains.

TRUE

False

Correct!

False is correct: According to the ASM guidelines, “Culture media and GBS isolation methods should detect both hemolytic and nonhemolytic strains…Nonhemolytic strains compose about 5-6% of GBS in screening specimens,* therefore careful scrutiny for non-hemolytic isolates is recommended.”

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*Citations can be found in the ASM guidelines

question 5

Why is it so important to accurately detect even low quantities of GBS in urine specimens from pregnant women?

Correlation with an increased risk of intrapartum colonization

Correlation with an increased risk of neonatal early-onset GBS disease

Any quantity is an indication for intrapartum prophylaxis

All of the above

Correct!

D is correct: According to the ASM guidelines, “In addition to standard of care culture work-up for potential causes of urinary tract infection, the American College of Obstetricians and Gynecologists (ACOG) recommends urine culture screening and reporting for GBS in any quantity from pregnant women.* Treatment of significant quantities (≥100,000 CFU/ml) of GBS in symptomatic patients is recommended and can reduce risk of pyelonephritis, low birth weight, and preterm birth in asymptomatic mothers.* Even low quantities of GBS in urine specimens correlate with anogenital colonization, increased risk of intrapartum colonization, and increased risk of neonatal EOD.* While treatment is not recommended for lower concentrations of asymptomatic GBS bacteriuria, any quantity is an indication for intrapartum prophylaxis…Specimens collected from pregnant women that require reporting of GBS in any quantity should be labeled or otherwise indicated during the ordering or collection process.”

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*Citations can be found in the ASM guidelines

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