Makindo Medical Notes

📖 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.