Lancefield grouping by latex agglutination identifies a beta-haemolytic streptococcus as Group B (Streptococcus agalactiae). In the diagnostic workup of a neonate with early-onset sepsis, which screening test is recommended for maternal colonisation status at 35–37 weeks gestation?
- A Vaginal swab Gram stain only
- B Vaginal and rectal swabs cultured on selective Todd-Hewitt broth with antibiotics ✓
- C Maternal serology for GBS capsular polysaccharide antibodies
- D Urine culture for GBS
Explanation
CDC and WHO recommend combined vaginal and anorectal swab culture in Todd-Hewitt broth supplemented with selective antibiotics (nalidixic acid + gentamicin or colistin + nalidixic acid) at 35–37 weeks gestation to detect GBS colonisation with maximum sensitivity (~87% versus ~40% for direct plating). Culture-based screening is preferred over serology because maternal antibody levels do not reliably predict neonatal protection. Urine GBS culture at any gestational age, if positive, indicates heavy colonisation and is also an indication for intrapartum prophylaxis.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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