Bacterial Gastrointestinal Infections Flashcards
What is the definition of Dysentery and enterocolitis
Dysentery - Blood and pus in the stool, usually accompanied by abdo pain and fever.
enterocolitis - Inflammation involving the mucosa of both small and large intestine
What are some of the natural barriers to GI infections?
Mouth - lysozyme enzymes,
Stomach - Acidic pH,
Small intestines - Mucous, bile, secretory IgA, lymphoid tissue, epithelial turnover and normal flora.
Large intestine - Epithelial turnover and normal flora
What are some potential bacterial GI pathogens and their source?
E. coli - Animal reservoir (eg, cattle), food or water borne.
Salmonella - Animal reservoir (reptiles), highly food borne and may be water borne.
Campylobacter - Mainly food borne (uncooked chicken) but can be animal or water borne.
Vibrio Cholera - Mainly water borne, no animal reservoir.
Shigella - Only food borne
Big 3 are Salmonella, Campylobacter and E.coli
What are the routes of transmission for GI infections
Faecal-oral route via 3 Fs; food, fingers and fluids.
Can have person to person transmission.
Explain the diagnosis of bacterial GI infections
- History; food history?, recent abx use? foreign travel? Nature of diarrhoea.
- Examination; febrile, shock, systemically unwell, neurological signs (think C. botulism)
- Investigations; Blood tests and blood film, sigmoidoscopy, abdo x ray and stool culture
What are the various approached for stool cultures?
- Enrichment broth; contains nutrients that promote growth of pathogen.
- Selective media; Supresses growth of background flora while allowing for growth of pathogen.
- Differential media; Distinguishes mixed microorganisms on the same plate eg, non-lactose fermenters and lactose fermenters
Explain the treatment of bacterial GI infections
- Most resolve spontaneously so the main focus is on fluid replacement as this is vital and life saving.
- Antibiotic treatment is reserved for severe/persistent infections. Abx in general GI infections may prolong/exacerbate symptoms
Describe features and pathogenesis of salmonella
- Gram negative bacilli which is often acquired via contaminated food, especially pork, poultry, milk/dairy products.
- Non-lactose fermenters.
- Diarrhoea occurs due invasion of epithelial cells in small intestines and subsequent inflammation.
- Bacteraemia may occur in extreme ages/immunocompromised.
Describe the clinical features of salmonella and the treatment
- Incubation period is 12-72 hours.
- Presents with watery diarrhoea, vomiting and fever. Duration is 2-7 days.
- Treatment; Fluid replacement is sufficient in most cases, antibiotics are saved for severe infections. As abx use and antimotility agents may prolong excretion of salmonellae in faeces.
Describe features and pathogenesis of Campylobacter
- Curved gram negative bacilli which is the commonest bacterial foodborne infection in the UK. Large animal reservoir especially poultry. Person to person spread is rare
- Bacterial invasion results in inflammation, ulceration and bleeding in bowel. Bacteraemia can occur in extreme ages or immunocompromised.
Describe the clinical features of campylobacter and the treatment
- Incubation period is 2-5days.
- Presentation; Bloody diarrhoea, cramping abdominal pain, (vomiting is rarely a feature), and fever. Duration is 2-10 days.
- Treatment; Fluid replacement is usually sufficient but if disease is severe/persistent then can give macrolides. Invasive disease can be treated with wuinolones
Describe features of Escherichia coli
- Gram negative bacilli which has 6 different diarrhoeagenic groups of E.coli;
- Enteropathogenic E. coli (EPEC)
- Enterotoxigenic E.coli (ETEC)
- Enterohaemorrhagic E. coli (EHEC)
- Enteroinvasive E. coli (EIEH)
- Entero-aggregative E.coli (EAEC)
- Diffuse aggregative E.coli
What is a rare complication of campylobacter infections?
-Post-infectious demyelination syndrome (guillian-barre) which is characterised by ascending paralysis
What is the most important campylobacter species?
C.jejuni
Describe the pathogenesis and presentation of enteropathogenic E.coli
Pathogenesis - Initial adherence via pili followed by formation of characteristic attaching and effacing lesion mediated by intimin protein and Tir with disruption to intestinal microvilli.
Clinical features - Incubation period of 1-2 days then presents with watery diarrhoea, vomiting and abdominal pain and fever. Can last from 1 to several weeks.
