TABLE 1

Overview and characteristics of laboratory methods for identification of group B streptococcus

Laboratory methodSpecial equipment requirementsSample typeTime to resultsRelative sensitivityaRelative specificityaRelative costsbAdvantagesDisadvantagesComments
Beta-hemolysisNoneClinical samples; isolated colonies requiredOvernight incubation to 2 days++++$Traditional, inexpensive, very easy to performFailure to detect nonhemolytic GBS strainsBeta-hemolysis may be difficult to observe
Granada-type mediaNoneClinical samples; isolated colonies in Granada agar requiredOvernight incubation+++++++++$Very easy to observe, 100% specific for GBSAnaerobic incubation, failure to detect nonhemolytic GBS strainsHighly discriminatory; anaerobiosis not required for Granada broths; frequently negative results for nonhuman GBS strains
Chromogenic mediaNoneClinical samples; isolated colonies required1–2 days++++++$Anaerobic incubation not necessaryGBS-like colonies require confirmatory testsSensitivity, specificity, and colony aspects vary among suppliers
CAMP testNoneIsolated colonies; previous culture isolation requiredOvernight incubation+++++++$Very easy to perform, easy to readRequires 1 additional day to confirm GBSAlso positive for Streptococcus porcinus and some group A streptococci
PYR testNoneIsolated coloniesMinutesAlways negative for GBSAlways negative for GBS$Easy to perform, commercially available from many suppliersAlways positive for group A streptococci; used to differentiate GBS from group A streptococci, enterococci, and S. porcinus
HippurateNoneIsolated coloniesMinutes+++$Easy to performToo unspecific for identification or confirmation of GBSPositive results for most GBS but also other streptococci
Biochemical profilingManual kits or automated systemsIsolated coloniesMinutes to overnight+++++Test, $$; platform, $$$Commercially available from many suppliersCostsNot widely used for identification of GBS; better to reserve kits for identification of other streptococcal species
MALDI-TOF MSMALDI-TOF MS instrumentIsolated coloniesMinutes++++++++Test, $; instrument, $$$$Easy and simple to performRequires specialized equipment, with high initial investment costsDisplacing phenotypic identification techniques in laboratories
Latex agglutination/coagglutinationNoneIsolated coloniesMinutes+++++++$Easy and simple to perform, available from many manufacturersS. pseudoporcinus and atypical enterococci (hemolytic) may cross-react with GBS grouping antisera
Direct antigen detectionNoneClinical samplesMinutes+++$Easy to perform, point-of-care testSensitivity insufficient for direct detection of GBS in clinical samplesCan help in diagnosis of neonatal GBS meningitis
PCR, clinical sampleAutomated PCR platformClinical sampleshours+++++++Test, $$; platform, $$$Can be performed at deliveryNo antibiotic susceptibility dataNot CDC recommended for GBS screening purposes
PCR, enrichment brothAutomated PCR platformEnrichment brothHours to overnight++++++++Test, $$; platform, $$$No clear advantage over culture-based methodsComplies with CDC recommendation
DNA sequencingDiagnostic molecular biologyIsolated coloniesDays++++++++++$$$Gold standard for taxonomic purposesRequires molecular biology expertiseVery rarely required to identify GBS
  • a Values for sensitivity and specificity estimates may be misleading because they depend on the test used for comparison. Thus, relative sensitivity and specificity are shown (from + to +++++).

  • b Costs can vary according to the location and laboratory testing volume.