Gastrointestinal Infections

Types

Organisms

Commonest

  • Campylobacter jejuni

  • Salmonella enteritidis

Others

  • Eschericia coli

  • Shigella sonnei (UK) (S. boydii, S. dysenterii, S. flexneri - tropical)

  • Vibrio cholerae

Watery Diarrhoeas

  • Caused by enterotoxins

    • activate adenylyl or guanylyl cyclase causing massively raised cAMP/cGMP

    • decrease activity of Na-glucose co-transporter

  • Organisms

    • (Vibrio cholerae)

    • Eschericia coli - Enterotoxic E. coli (ETEC)

  • Treatment

    • oral rehydration - sodium and glucose

    • antibiotics only if seriously ill or need to terminate an outbreak

      • tetracycline

      • doxycycline

Bloody Diarrhoeas

  • caused by cytotoxins

    • interfere with protein synthesis / ribosomes

  • organisms

    • Shigella

    • E. coli O157 - entero-haemorrhagic E. coli (EHEC)

    • Clostridum difficile

      • causes antibiotic-associated colitis (pseudomembranous colitis if diagnosed by endoscopy)

    • Salmonella

  • Treatment

    • oral rehydration

    • ciprofloxacin if systemically unwell

    • if Salmonella

      • can get asymptomatic carriage in kidney and gall-bladder

      • so ciprofloxacin + cholecystectomy

Enteric Fevers

  • Salmonella typhi

  • Salmonella paratyphi

do NOT confuse with Salmonella typhimurium which causes diarrhoea

  • systemic infections acquired through GI tract

  • do not give diarrhoea - S. typhi often causes constipation

    • need blood cultures not stool samples

    • but can get GI complications

      • haemorrhage

      • perforation

  • exclusively human reservoirs - so person to person spread

  • Treatment

    • ciprofloxacin always

    • may need cholecystectomy to remove carriage

  • Vaccine( Ty21a) - IM or oral is 70% effective

Intoxications

  • bacteria multiply in (for example) food stuff and produce toxin
  • when ingested there is no need for bacteria to multiply and onset of symptoms rapid
  • Examples
    • Clostridium botulinum (botulism)
    • Staphylococcus aureus
      • from lesions on food handlers
      • onset about 6 hours
    • Bacillus cereus

Complications

  • Guillain-Barre syndrome
    • associated with Campylobacter

Diagnosis

  • Microscopy
  • Culture
    • indicator plates - e.g. McConkey's agar turns pink with lactose fermenters (normal flora)
    • Campylobacter
      • needs to be at 43oC
      • special agar
  • Serology
    • ELISA
      • C. difficile toxin in stool samples
      • Entamoeba histolytica
  • (molecular biology techniques)