This covers Streptococcus agalactiae, the organism responsible for GBS infections in pregnancy + neonates.

⭐ THE 20% THAT GIVES 80% MARKS (SUPER HIGH-YIELD)

1. Organism:

Streptococcus agalactiae = Group B Streptococcus (GBS)

Gram-positive cocci, chains, β-hemolytic, catalase-negative.

2. Key features:
• Polysaccharide capsule (main virulence factor)
• CAMP test positive
• Hippurate positive
• Bacitracin resistant
• Narrow-zone beta hemolysis
3. Where it lives:
• Normal flora of vagina
• Gastrointestinal tract
4. Transmission:
• From mother → baby during delivery
• Ascending infection (in utero)
• Rare: sexual transmission in adults
5. Diseases (VERY HIGH-YIELD):
• Neonates:
• Early onset (within 1 week): sepsis, pneumonia, respiratory distress
• Late onset (1 week–3 months): meningitis
• Pregnancy: chorioamnionitis, postpartum endometritis
• Adults (diabetics, elderly): bacteremia, UTI, soft tissue infections
6. Diagnosis:
• Culture at 35–37 weeks in all pregnant women
• Selective media (granada agar, carrot broth)
• CAMP test, hippurate test
7. Prevention:
• Intrapartum prophylaxis: IV Penicillin G (drug of choice)
• Alternatives: ampicillin; clindamycin if allergic
• Give if positive screening OR risk factors
8. Treatment:
• Neonatal sepsis/meningitis:
• Ampicillin + gentamicin
• Adult infections: Penicillin/ampicillin
9. Important exam fact:

GBS = #1 cause of neonatal sepsis and meningitis.

Memorize this block → you score 80–100% on exams.

🔬 FULL MICROBIOLOGY – CLEAR & COMPLETE

1️⃣ Classification

• Gram-positive
• Cocci in chains
• β-hemolytic (narrow zone)
• Catalase-negative
• Lancefield Group B
• Bacitracin resistant
• CAMP test positive
• Hippurate positive

2️⃣ Virulence Factors (Exam Favourites)

1. Polysaccharide capsule
• MOST IMPORTANT
• Prevents phagocytosis
2. β-hemolysin
• Lyses RBCs
• Helps tissue invasion
3. CAMP factor
• Enhances hemolysis of Staph aureus
• Basis of CAMP test positivity
4. Surface adhesins

3️⃣ Reservoir & Transmission

❗ Natural reservoir:

• Vagina (20–30% colonized)
• GI tract

❗ Transmission:

• During vaginal delivery
• Ascending infection during pregnancy
• Breast milk (rare)

Risk ↑ with:

• Prolonged rupture of membranes
• Preterm labor
• Maternal fever
• Previous infant with GBS disease

4️⃣ Clinical Disease

A. Neonatal Disease (Most Important)

Early-onset disease (0–6 days)

• From intrapartum infection
• Symptoms:
• Sepsis (most common)
• Pneumonia
• Respiratory distress
• Hypotension
• Lethargy
• High mortality

Late-onset disease (7–90 days)

• From postpartum exposure
• Symptoms:
• Meningitis
• Seizures
• Fever
• Bulging fontanelle
• High risk of neurological damage

📌 Exam tip:

Early = sepsis/pneumonia, Late = meningitis.

B. Maternal Disease

• Chorioamnionitis
• Endometritis
• UTI
• Bacteremia

C. Adult Disease

Seen in diabetics, elderly, immunosuppressed:

• Skin/soft tissue infections
• Osteomyelitis
• Septic arthritis
• Bacteremia
• Pneumonia

5️⃣ Diagnosis

A. Prenatal screening at 35–37 weeks

• Vaginal + rectal swab
• Culture in selective media (LIM broth, carrot broth)

B. Laboratory tests

• Gram-positive cocci in chains
• β-hemolysis (narrow)
• CAMP test positive
• Arrowhead hemolysis pattern with Staph aureus
• Hippurate hydrolysis positive
• Bacitracin resistant
• PCR available but not widely used

6️⃣ Treatment

A. Neonatal GBS infection

• Ampicillin + gentamicin
• Switch to cefotaxime if meningitis suspected

(SC note: Avoid ceftriaxone in neonates.)

B. Adults

• Penicillin G
• Ampicillin
• Cephalosporins

7️⃣ Prevention (VERY HIGH-YIELD)

Intrapartum antibiotic prophylaxis (IAP) if:

➡ Mother GBS positive

➡ Previous baby with GBS infection

➡ GBS bacteriuria during pregnancy

➡ Unknown GBS status + risk factors

• Fever in labor
• ROM > 18 hours
• Preterm labor

Drugs:

• Penicillin G IV every 4 hours until delivery
• Ampicillin is alternative
• If allergic (non-anaphylaxis): cefazolin
• If anaphylaxis risk → clindamycin (if sensitive) or vancomycin

8️⃣ High-Yield Comparisons

GBS vs Listeria (neonatal meningitis)

⭐ THE MUST-MEMORISE SUMMARY

1. GBS = Streptococcus agalactiae, Gram+ cocci in chains, β-hemolytic.
2. CAMP positive, hippurate positive, bacitracin resistant.
3. #1 cause of neonatal sepsis & meningitis.
4. Early onset → sepsis/pneumonia; Late onset → meningitis.
5. Lives in vagina + GI tract.
6. Screen all pregnant women at 35–37 weeks.
7. Prophylaxis = IV Penicillin G during labor.
8. Treatment of neonatal disease = ampicillin + gentamicin.
9. Capsule = major virulence factor.
10. Risk ↑ with PROM, preterm labor, maternal fever.

🧫 STREPTOCOCCUS AGALACTIAE (GBS) — COMPLETE MASTER TABLE SET

🦠 1️⃣ ORGANISM IDENTIFICATION (EXAM SNAPSHOT)

🧬 2️⃣ VIRULENCE FACTORS (EXAM FAVOURITES)

🏠 3️⃣ RESERVOIR & COLONIZATION

🔁 4️⃣ TRANSMISSION

🔺 Risk factors increasing transmission

Risk factor

Prolonged rupture of membranes (>18 h)

Preterm labor

Maternal fever

Previous infant with GBS disease

GBS bacteriuria in pregnancy

👶 5️⃣ CLINICAL DISEASE — NEONATAL (HIGHEST YIELD)

A. Early-Onset Disease (0–6 days)

B. Late-Onset Disease (7–90 days)

📌 Exam lock:

Early = sepsis/pneumonia

Late = meningitis

🤰 6️⃣ MATERNAL DISEASE

Condition

Chorioamnionitis

Postpartum endometritis

UTI

Bacteremia

🧓 7️⃣ ADULT DISEASE (RISK GROUPS)

🧪 8️⃣ DIAGNOSIS

A. Prenatal Screening

B. Laboratory Identification

💊 9️⃣ TREATMENT

A. Neonatal GBS Infection

B. Adult Infection

Drug options

Penicillin G

Ampicillin

Cephalosporins

🛡️ 🔟 PREVENTION — INTRAPARTUM ANTIBIOTIC PROPHYLAXIS (VERY HIGH-YIELD)

Indications for IAP

Give IAP if ANY present

GBS positive screening

Previous baby with GBS disease

GBS bacteriuria in current pregnancy

Unknown status + fever

Unknown status + ROM >18 h

Unknown status + preterm labor

Drugs for IAP

🆚 1️⃣1️⃣ HIGH-YIELD COMPARISON — GBS vs LISTERIA