Salmonella enterica
📖 About
- Salmonella enterica → a highly motile, Gram-negative bacterium in the Enterobacteriaceae family.
- Non-lactose fermenting;>2000 serotypes (e.g. Typhimurium, Enteritidis, Dublin, Choleraesuis).
- Major global cause of foodborne gastroenteritis.
🔬 Characteristics
- Motile Gram-negative rods; facultative anaerobes.
- Ferment glucose but not lactose → pale colonies on MacConkey agar.
- 🧪 Oxidase-negative, catalase-positive, reduce nitrates → nitrites.
- Antigens:
- H antigen: flagellar, motility.
- O antigen: somatic, LPS-related.
- Vi antigen: capsular virulence factor (esp. *S. Typhi*).
- Bile salt resistant → survival in intestinal tract.
🏠 Source
- Foodborne: undercooked poultry, raw eggs, unpasteurised milk.
- Risk groups: infants 👶, elderly 👵, reduced gastric acid (e.g. PPI users).
- ⚠️ Sickle cell disease → predisposes to invasive salmonella infection, esp. osteomyelitis.
⚠️ Pathogenicity
- Most commonly → gastroenteritis (self-limiting).
- Watery diarrhoea (may be inflammatory with mucus/blood).
- Abdominal cramps, nausea, vomiting, fever.
- Septicaemia → uncommon but can occur in immunocompromised (HIV, malignancy, extremes of age).
- Focal infections (rare): osteomyelitis, meningitis, endocarditis.
💊 Sensitivities
- Traditionally sensitive to ciprofloxacin & fluoroquinolones.
- ⚠️ Increasing resistance (MDR *Salmonella*) → culture and sensitivity essential.
🩺 Management
- 💧 Supportive therapy → oral rehydration/IV fluids mainstay in gastroenteritis.
- 💊 Antibiotics:
- Not required in most cases (may prolong carriage).
- Indicated if severe/systemic disease, immunocompromised, infants, elderly.
- Agents: Ciprofloxacin, ceftriaxone, azithromycin (guided by sensitivity).
- 🛡️ Prevention: safe food handling, proper cooking, pasteurisation, hand hygiene.
⚠️ Exam pearl:
Salmonella enterica (non-typhoidal) → foodborne gastroenteritis, usually self-limiting.
In sickle cell disease, it is the classic cause of osteomyelitis.
