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Flashcards in Intestinal Infections Deck (61)
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What types of damage can be caused by gastrointestinal pathogens?

  • Local inflammation
  • Ulceration / perforation of mucosal epithelium
  • Disruption of normal microbiota
  • Pharmacological action of bacterial toxins
  • Invasion to blood or lymphatics


Describe the consequences of GI epithelial perforation.

  • Ruptured ulcer / perforated ulcer.
  • Lining of the mucosa wall is perforated due to untreated ulcers.
  • May result in leaking of food and gastric juices to the peritoneal or abdominal cavities.
  • Treatment requires surgery.


What are the incubation periods for the pathogens which cause diarrhoea, specifically campylobacter and shigella?

  • Campylobacter - 2-11 days
  • Shigella - 1-4 days


What are the durations of diarrhoea caused by campylobacter and shigella?

  • Campylobacter - up to 3 weeks
  • Shigella - 2-3 days


Describe the variable symptoms caused by the pathogens which cause diarrhoea, specifically campylobacter, shigella, EPEC and cholera.

  • Campylobacter and shigella - bloody stools. 
  • EPEC and cholera - watery stools. 


Describe the characteristics of vibrio cholerae.

  • Gram negative
  • Comma-shaped rod
  • Flagellated
  • Characterised by epidemics and pandemics
  • Human-only pathogen
  • Flourishes in communities with no clean drinking water / sewage disposal


What are the available vaccines for V. Cholerae?

  • Parenteral vaccine: low protective efficiency. 
  • Oral vaccine: effective and suitable for travellers. 


Describe the pathogenesis of V. cholerae.

  • Only infective in large doses.
  • Many organisms killed in the stomach. 
  • Colonisation of small intestine involving flagellar motion, mucinase, attachment to specific receptors.
  • Production of multicomponent toxin. 
  • Loss of fluid and electrolytes without damage to enterocytes. 


Describe the characteristics of the cholera toxin (CTx). 

  • Oligomeric complex of 6 protein subunits:
    • 1 copy of A subunit (enzymatic)
    • 5 copies of B subunit (receptor binding)
  • Responsible for the characteristic, watery cholera diarrhoea. 


Describe the consequences of being infected by cholera.

  • Fluid loss of up to 1L per hour. 
  • Electrolyte imbalance leading to dehydration, metabolic acidosis and hypokalaemia. 
  • Hypovolaemic shock.
  • 40-60% mortality. 
  • <1% mortality if given fluid / electrolytes (ORT).


Describe the characteristics of Escherichia coli. 

  • Gram negative.
  • Bacillus.
  • Member of normal GI microbiota.
  • Some strains possess virulence factors enabling them to cause disease. 


What are the types of E. coli which cause GI infections?

  • EPEC - enteropathogenic
  • ETEC - enterotoxigenic
  • VTEC / STEC - verocytotoxin-producing
  • EHEC - enterohaemorrhagic
  • EIEC - enteroinvasive
  • EAEC - enteroaggregative


Describe the different GI infections caused by the different types of E. coli. 

  • EPEC: sporadic cases and outbreaks of infection in under 5s. 
  • ETEC: 'travellers' diarrhoea' (occurs in 20-50% of travellers). 
  • VTEC / EHEC: sporadic cases and outbreaks of gastroenteritis. 
  • EIEC: food-borne infection in areas of poor hygiene (often persistent diarrhoea). 
  • EAEC: resource-poor countries. 


Describe the factors which aid the adherence of E. coli.

  • Pili / fimbriae are used to attach the bacteria onto enterocytes. 
  • Pedestal formation - this happens normally even in the absence of infection. 


Describe the mode of action of E. coli enterotoxins. 

  • LT = heat-labile toxin
  • STa = heat-stable toxin


Describe the characteristics of campylobacter jejuni.

  • Gram negative. 
  • Helical bacillus. 
  • Large animal reservoir. 
  • Causes food-associated diarrhoea. 
  • Commonest cause of diarrhoea in the developed world. 
  • Transmission through comsumption of raw / undercooked meat, contaminated milk. 
  • Mucosal inflammation and fluid secretion. 


Describe the histological appearance of C. jejuni infection.

  • Inflammation involves entire mucosa.
  • Villous atrophy.
  • Necrotic debris in crypts.
  • Thickening of basement membrane. 


Describe the characteristics of Salmonella spp.

  • Gram negative. 
  • Bacilli.
  • >2000 serotypes of Salmonella spp.
  • Causes food-associated diarrhoea.
  • Transmission through consumption of raw / undercooked meat, contaminated eggs and milk. 
  • Secondary spread can be human - human. 
  • Important species:
    • S. typhi
    • S. paratyphi
    • S. enteritidis


Describe the pathogenesis of Salmonella infection.

  • Ingestion of large numbers of bacteria. 
  • Absorption to epithelial cells in terminal section of the small intestine. 
  • Penetration of cells and migration to lamina propria. 
  • Multiplication in lymphoid follicles. 
  • Inflammatory response mediates release of prostaglandins. 
  • Stimulation of cyclic AMP. 
  • Release of fluid and electrolytes causing diarrhoa. 


Describe the consequences of S. typi and S. paratyphi infections. 

  • Cause enteric fevers: typhoid and paratyphoid. 
  • Systemic infections initiated in gastrointestinal tract.
  • Species restricted to humans. 
  • Multiply within, and are transported around the body in, macrophages. 
  • Patients can excrete S. typhi in faeces for several weeks after recovery.
  • 1-3% become chronic carriers, most common in women and the elderly. 
  • Public health concern:  it is a notifiable disease. 


What are the available vaccines for typhoid?

  • Oral; live attenuated
    • Booster after 5 years
  • Parenteral; capsular polysaccharide 
    • Booster after 2 years
  • 50-80% effective.
  • Recommended for travellers to endemic areas. 


Describe the characteristics of shigella spp. and name the 4 species. 

  • Bacillus.
  • Causes shigellosis (bacillary dysentery).
  • Human-only pathogen. 
  • 4 species:
    • S. dysenteriae: most serious
    • S. flexneri: severe disease
    • S. boydii: severe disease
    • S. sonnei: mild infections 


Describe the pathogenesis of shigella infection.

  • Attaches to mucosal epithelium of distal ileum and colon. 
  • Causes inflammation and ulceration. 
  • Rarely invasive.
  • Produces Shiga toxin (STx). 
  • Diarrhoea watery initially, later can contain blood and mucous. 
  • Disease is usually self-limiting. 


Describe the characteristics of listeria monocytogenes. 

  • Coccobaccillus. 
  • Causes listeriosis. 
  • Food-borne pathogen associated with paté, soft cheese, unpasturised milk, hummus. 
  • <1000 organisms may cause disease. 
  • Population at risk:
    • Pregnant women (with possibility of infection of the baby in utero or at birth). 
    • Immunosuppressed individuals (e.g. those with AIDS or on cancer / immunosuppressive drugs). 
    • The elderly.
  • Usually presents as meningitis. 


Describe the characteristics of antibiotic-associated diarrhoea.

  • Does NOT involve ingestion of pathogen or toxin. 
  • Can arise from disruption of gut microbiota following antibiotic therapy. 
  • Tetracycline - allows colonisation by Staphyloccocus aureus & Candida sp.
  • Clindamycin suppresses gut microbiota and allows Clostridium difficile to multiply - overgrowth. 
  • C. difficile infection is now associated with resistance to vancomycin. 


Describe C. difficile infections.

  • Produces spores for survival.
  • Produces an enterotoxin and a cytotoxin.
  • Nosocomial infections largely responsible for increase in cases. 


Describe Clostridium perfringens infection.

  • Usually caused by type A strains from animal guts and soil. 
  • Contamination of raw meat products. 
  • Spores survive cooking and germination takes place. 
  • Multiplication in large intestine, production of spores and enterotoxin. 
  • Damage to intestinal epithelium. 
  • Diarrhoea. 


Describe Rotavirus.

  • 'Rota' = wheel. 
  • 11 separate segments of double-stranded RNA. 
  • Infects many mammals. 
  • Infection commonest in children <2 years old.
  • As few as 10 ingested particles can cause disease. 
  • Seasonal ocurrence (commonest in cooler months).
  • Transmission is faeco-oral, but may also be faeco-respiratory. 


Describe the pathogenesis of rotovirus infection. 

  • Incubation period of 1-2 days.
  • Replication of virus in small intestinal epithelial cells at tips of villi. 
  • Results in villous atrophy. 
  • Damage caused to infected cells leaving immature cells with reduced absorptive capacity for sugar, water and electrolytes. 
  • Onset of vomiting, diarrhoea lasting 4-7 days.
  • Up to 1010 - 1011 virus particles / gram faeces released. 


What are the available vaccines for rotavirus?

  • RotaRix; RotaTeq
    • Oral administration (2-3 doses)
    • First dose at 6-10 weeks of age
    • Live, attenuated virus
  • Introduced in UK from 2013.