Salmonella typhi
📖 About
- Salmonella typhi is a highly motile, non-lactose fermenting member of the Enterobacteriaceae family.
- Causes Typhoid fever (enteric fever), a systemic illness.
🔬 Characteristics
- Gram-negative motile rods, facultative anaerobes.
- Glucose fermenting; oxidase-negative, catalase-positive.
- Reduce nitrates → nitrites.
- Non-lactose fermenting → pale colonies on MacConkey agar.
- Resistant to bile salts (sodium deoxycholate).
- Possesses a polysaccharide capsule (Vi antigen) which inhibits phagocytosis.
🏠 Source
- Humans are the only reservoir.
- Spread by the “4 Fs”: food, fingers, faeces, flies.
- Chronic carriage (e.g. via biliary tract) may occur → public health risk.
⚠️ Pathogenicity
- Typhoid fever:
- Bacteria invade the ileocaecal region → Peyer’s patches → bloodstream.
- Engulfed by macrophages but survive, spreading via the reticuloendothelial system.
- Chronic carriage possible (esp. gallbladder).
- Clinical features:
- Headache, anorexia, malaise, lethargy.
- High fever (often stepwise, up to 40°C).
- Abdominal pain, constipation (diarrhoea usually appears in week 2).
- Rose spots on the abdomen (transient, blanching rash).
- Splenomegaly, mesenteric lymphadenopathy.
- Complications:
- Splenic rupture.
- Intestinal perforation or haemorrhage (necrosis of Peyer’s patches).
- Cholecystitis (site of carriage).
💊 Sensitivities
- Ciprofloxacin traditionally first-line, but resistance is increasingly common worldwide.
- Other options (guided by sensitivity): ceftriaxone, azithromycin.
🩺 Management
- Antibiotics: Ciprofloxacin if sensitive; otherwise ceftriaxone or azithromycin.
- Supportive care: Rehydration, antipyretics, nutritional support.
- Public health: Notify local health authorities (UK = notifiable disease). Screen close contacts, exclude carriers from food handling.
⚠️ Exam pearl: Typhoid fever presents with stepwise fever, rose spots, constipation (not diarrhoea early), splenomegaly, and can cause intestinal perforation. Chronic carriage occurs via the gallbladder.
