Colonisation

• The establishment of a microorganism on or within a host; it may be short lived

Gram-negatives in the GI tract

Enterobacteriaceae

• Gram negative coliform
• 53 genera, 26 of which cause human infection
• Facultative anaerobes mostly
• Ferment sugars

How Enterobacteriaceae cause disease

• Colonisation factors – fimbriae bind tightly to host tissue
• Endotoxin - cell wall component (LPS – shock, fever, hypoglycaemia
• Enterotoxin - toxin released by the bacteria

Gram-positives in the GI tract

Normal flora of the bowel

• Mouth - Strep. ‘viridans’, Neisseria sp., anaerobes
• Stomach/duodenum - usually sterile due to low pH, few Candida sp. And Staphylococci may survive
• Jejunum - small numbers of coliforms and anaerobes
• Colon (‘faecal flora’) - large numbers of coliforms, anaerobes (Clostridium sp., Bacteroides sp., and anaerobic cocci) and Enterococcus faecalis
• Bile ducts - usually sterile

MALDI-TOF mass spectrometry