Serratia
📖 About
- Member of the Enterobacteriaceae family: Gram-negative, non-lactose fermenting rods.
- Notable species: Serratia marcescens.
- Historically known for producing a distinctive red pigment (prodigiosin), sometimes seen in colonies.
🔬 Characteristics
- Gram-negative rods.
- Facultative anaerobes.
- Glucose fermenting.
- Oxidase-negative, catalase-positive.
- Reduce nitrates → nitrites.
- Non-lactose fermenters → pale colonies on MacConkey agar.
- Motile via peritrichous flagella.
- Often demonstrate intrinsic resistance to multiple antibiotics (Ampicillin, first-gen cephalosporins).
⚠️ Pathogenicity
- 💧 Urinary Tract Infections (UTIs): Often linked to indwelling catheters (CAUTIs); symptoms: dysuria, frequency, fever.
- 🫁 Respiratory Tract Infections: Ventilator-associated pneumonia (VAP); cough, fever, hypoxia.
- 🩸 Bacteraemia / Sepsis: Secondary to UTIs, VAP, or IV lines; features: fever, rigors, hypotension, confusion.
- 🩹 Wound & Burn Infections: Redness, swelling, pain, purulent discharge; problematic in surgical/ICU settings.
- ❤️ Endocarditis: Rare but serious; associated with IV drug use or prosthetic valves → fever, murmur, heart failure signs.
- 🧠 Meningitis: Rare; usually neonates or immunocompromised; fever, neck stiffness, altered mental status.
🎯 Risk Factors
- 🏥 Hospitalisation: Particularly in ICUs and surgical wards.
- 🛡️ Immunocompromise: HIV, neutropenia, chemotherapy, transplant patients.
- 🧴 Indwelling devices: Catheters, central venous lines, ventilators.
- 🔧 Recent surgery: Especially with prosthetic implants or long operative times.
🖥️ Imaging
- 🫁 Respiratory infection: CXR or CT chest.
- ❤️ Endocarditis: Echocardiography (TEE preferred).
- 🧾 Abscess / deep infection: Ultrasound or CT scan.
💊 Management (key points)
- Always guided by culture & sensitivity (multidrug resistance is common).
- Empiric options: carbapenems, aminoglycosides, or cefepime (depends on local resistance patterns).
- Device-associated infections → removal/replacement of catheter or line is essential.
- Supportive care: IV fluids, oxygen, source control.
⚠️ Exam pearl: Serratia marcescens is a classic cause of hospital-acquired UTIs, pneumonias, and device-related sepsis, notable for red pigment and multidrug resistance.
