Bacteria affecting the GIT Flashcards
Define Gastroenteritis
Syndrome characterised by GI-symptoms including nausea, vomiting, diarrhoea and abdominal pain
Define Diarrhoea
Abnormal faecal discharge characterised by frequent and/or fluid stool. Associated with increased fluid and electrolyte loss- often disease of small intestine
Define Dysentery
Abnormal inflammation of GI-tract: often blood and pus in faeces and pain, fever, abdominal cramps- often disease of large intestine
Define Enterocolitis
Inflammation of mucosa of small and large intestine
Defences of the mouth?
Flow of liquids
saliva
lysozyme
normal bacterial flora
Defences of the oesophagus?
flow of liquids
peristalsis
Defences of the stomach?
Gastric Acid pH 1-2
Defences of the small intestine?
flow of gut contents peristalsis mucus, bile secretory IgA lymphoid tissue shedding and removal of epi
Defences of the large intestine?
Normal flora
peristalsis
shedding and replication of epi
mucus
What is food poisoning?
Ingestion of toxins or poisons in food: e.g. bacterial toxins or heavy metals
Bacteria grow and multiply in food
Cooking kills bacteria but toxin still active – intoxication
Staphylococcus aureus in food poisoning?
Growth in food after human contamination> mainly dairy, cooked meats
50% of strains produce heat stable enterotoxins - resistant to stomach acid and digestive enzymes
3-6hrs of severe vomiting
Complete recovery
Botulism: Clostridium botulinum in food poisoning?
Heat stable toxin ingested in food, leads to flaccid paralysis and death
Infant botulism most common
What is bacillus cereus in?
Fried rice - gram positive, heat resistant spore former
What bacteria infects the lower GIT?
Ones that resist the low pH of the stomach
What causes gastric ulcers?
Helicobacter pylori
How is helicobacter pylori resistant to stomach acid?
Produces urease - turns urea to ammonia and co2
= Protective cloud during transit to gastric mucin layer
Ammonia basis of breath test
How to treat diarrhoea?
Fluid and electrolyte replacement
Antibiotic treatment often not successful and may worsen problem
Why may antibiotic treatment worsen diarrhoea?
They wipe out competing organisms or stimulates toxin production
Diarrhoea - E.coli features?
Gram-negative motile rod
Major cause of diarrhoeal disease and gastroenteritis worldwide
Complications include HUS
Many genetically distinct disease causing strains
Some strains reside in normal commensal flora
Others infect urinary tract and cause meningitis
Diarrhoea: Ingested in food or via fecal-oral transmission route.
Genetic diversity dependent on plasmid, lysogenic phage and transposon encoded ‘pathogenicity islands’
How to detect E.coli?
Lactose fermentation - MacConkey agar
PCR/antigen tests for serotypes
EPEC features?
Bundle-forming pili important in attachment
Type III secretion system injects proteins into host to manipulate cytoskeleton:
Tir- translocated intimin receptor
Intimin- mediates intimate attachment to epithelial cells
Attaching and effacing lesion
Leads to watery diarrhoea
How does ETEC work?
Attach via adhesive pili
Produce Heat Stable (ST) and Labile (LT) enterotoxins (cholera like) that cause diarrhoea
What does ETEC commonly cause?
Travellers diarrhoea OR Delhi Belly! (No blood) (cholera like in some cases)
What does EIEC do? What does it cause?
Invade and destroy epithelial cells
Causes bloody diarrhoea
EHEC features?
Attachment similar to EPEC- pedestals
Produce Vero-toxin (Also called Shigella-like toxin)- STx
STx (verotoxin) is a potent diarrhoeal toxin (and has receptor on kidney cells) acts via damaging cells directly
EHEC infections also cause hemorrhagic colitis- Bloody diarrhoea- destruction of mucosa>bleeding> spread to kidneys
HUS- Haemolytic Urinary Syndrome
-This may lead to kidney failure (15% cases)
- O157:H7 strain most well known
Shigella features?
Shiga toxin producing (similar to EHEC)
Shigella dysenteriae
– bacillary dysentry, Bloody stools
Shigella sonnei and flexneri
milder forms
Low infectious dose 10-100 cells – sometimes ID50
Non-lactose fermenters (Maconkey agar, Hektoen enteric- green no H2S)
Common in poorer countries
Spread fecal-orally, often via water contamination
Salmonella features?
Historically most common food-associated pathogen in UK- FORMER NO.1 CAUSE IN UK
Spread from food- mainly chicken and dairy products, but also person to person
Invade M-cells then spread to surrounding epithelium
Usually a severe but self-limiting diarrhoea and enterocolitis
Salmonella enterica subsp. Cause uncomplicated diarrhoea
- typhimurium
- enteritidis
Lab detection of salmonella?
MacConkey agar
Non-lactose fermenter
S.typhi features?
Cause of typhoid fever
Infection initiates in the intestine
Spreads systemically- transported in macrophages around body
seed many organs before further spread
causes increasing fever over 14 days»_space; GI symptoms
Pre-antibiotics 12-16% died
Complications:
GI lesions and haemorrhage
toxaemia- endocarditis
Meningitis
Vi antigen vaccine recommended for travel
1 – 3 % become carriers »_space; gall-bladder
What is the number 1 cause of food poisoning in the UK?
Campylobacter spp.
Campylobacter spp. features? (also known as helicobacter pylori)
Gram-negative micro-aerophiles
Campylobacter jejuni most common
Acquired by ingestion of contaminated food
Major reservoir in Chickens> 75% of all we buy have colonisation
Symptoms like Shigellosis and Salmonellosis:
- ulceration (jejunum), diarrhoea up to 10 movements per day…
- longer lasting illness- up to 3 weeks!
- complications: Guillame Barre and reactive arthiritis
What is the number 1 cause of food poisoning worldwide?
Cholera
What causes cholera?
Caused by motile Gram-negative comma-shaped bacterium
Cholera prevalence?
Estimated 1.3-4 million cholera cases and 21000–140 000 deaths due to cholera every year- mainly developing countries
How does the cholera toxin work regarding water flow?
ADP-ribosylation of G-protein signalling pathways causes increased secretion of Chloride ions
This prevents influx of Sodium ions into cells
Results in rapid loss of water from tissue- massive diarrhoea
= rapid fluid loss of 1-3 litres per hour
How to treat cholera?
Rapid fluid and electolyte replacement required or dehydration and death result
Symptoms of cholera when severely dehydrated?
Unconscious, floppy Sunken and dry eyes Absent tears V dry mouth and tongue Drinks poorly or cannot drink Skin pinch - goes back very slowly
How to prevent cholera?
Unsuccessful vaccine
Improve water system and sanitation
Where are viral causes of GI infections most likely? How are they spread?
Developing countries
Mainly oral-fecal spread
Rotavirus features?
Wheel-like viral particle Diarrhoea caused by tissue damage in small intestine Dehydration main risk Very low-infectious dose Very contagious V resistant to celaining products
Winter virus features?
Norovirus (Norwalk viruses) - not cultivated
Chills, headache, fever, nausea, vomiting, v-low infectious doses (10).
recovery in 24 – 48 hours
Common in hospital settings …. Hard to clean away
How is the cholera toxin produced?
Vibrio cholerae ingested
Large doses needed to cause disease unless on antibiotics and acholorhydric
Sensitive to stomach acid
Small intestine colonisation depends on: motility, production of mucinase attachment to specific receptors
Toxin production
Massive loss of fluid and electrolytes
