Enterobacteriaceae and Gut Diseases

Enterobacteriaceae
1. Small, Gram -ve rods (2-5 by 0.5 um)
  1. Inner membrane - phospholipid bilayer
    1. Solid membrane - murein layer, muopeptide, peptidoglycan
      1. Outer membrane - lipopolysaccharide, lipoprotein (and O antigen repeat side chains)
        LPS is involved in shock, fever, hypoglycaemia, DIC, thrombosis, vascular permeability, hypotension and decreased iron levels
2. Mostly motile with peritrichious flagella (except Shigella and Klebsiella)
3. Oxidase negative facultative anaerobes
4. Reduce nitrate and ferment glucose (and other carbohydrates)
5. Some strains are opportunistic pathogens, some are true pathogens (Salmonella, Yersinia, some E. coli, Shigella)
6. Many genera: Escherichia, Salmonella, Shigella, Yersinia, Klebsiella, Proteus, Enterobacter etc.
7. Sites of infection
  1. CNS - Escherichia
  2. Bloodstream - Escherichia, Enterobacter, Klebsiella
  3. Lower respiratory tract - Klebsiella, Enterobacter, Eshcerichia
  4. Gastrointestinal - Salmonella, Escherichia, Shigella, Yersinia
  5. Urinary tract - Proteus, Escherichia, Klebsiella, Providencia
8. Different genera have different antigens on their capsule
  1. E. coli - K antigen, S. typhi - Vi antigen, K. pneumonia - serotype antigen
Exotoxins vs Endotoxins
1. Exotoxins
  1. Released from the cell before or after lysis
  2. Are proteins
  3. Heat-labile
  4. Antigenic and immunogenic
  5. Toxoids can be produced
  6. Specific effect on host
  7. Profuced by Gram -ve and +ve bacteria
2. Endotoxins
  1. Integral part of cell wall
  2. Are LPS - lipid A is the toxic component (hydrophobic fatty acids)
  3. Heat-stable
  4. Antigenic
  5. Toxoids cannot be produced
  6. Many effects on host
  7. Produced by Gram -ve organisms only
Bacillary Dysentry (Shigellosis)
1. Acute infectious disease of the intestines caused by dysentery bacilli
2. Symptoms
  1. Fever
  2. Abdominal pain
  3. Diarrhoea
  4. Tensmus (constant feeling of needing to defacate)
  5. Stool mixed with mucus, blood and pus
  6. Shock and toxic encepalopothy
3. Etiology
  1. Gram -ve, short rod, non-motile
  2. Shigella
  3. 4 groups, 47 serotypes
    1. S. dysenteriae is the most severe
    2. S. flexneri causes epidemics and can become chronic
    3. S. boydii found in tropical areas
    4. S. sonnei is the most mild
4. Pathogenicity
  1. Endotoxins and interotoxins (exotoxins)
  2. Invasiveness
    1. Attach-penetrate-multiply
  3. Resistance - strong
    1. Can survive 1-2 weeks on fruit/vegetables/soil
      1. Destroyed by heating for 30 mins at 60 'C
5. Transmitted via faecal-oral route
6. Immunity is short and unsteady - no cross-immunity
7. Treated with Quinolones
8. Features
  1. Diffuse fibrous exudative inflammation and lesions in sigmoid and rectum with superficial ulceration
  2. Hyperemia, oedema, leukocyte infiltration and necrosis
Shigella Infection
1. Bacteria enters intestine
  1. Normal bacterial flora and sIgA prevent attachment
  2. Bacteria penetrate mucus and multiply in epithelial cells and propria lamina
    1. Inflammation and vessel contraction
      1. Superficial mucosal necrosis and ulcer
        Diarrhoea mixed with blood, pus and mucus with abdominal pain
    2. Endotoxin
      1. Endogenous pyrogen
        Fever
      2. Allergy to endotoxin
        Increased dimethyl-adrenaline
        Micro-circulatory failure
        Shock, Disseminated Intravascular Coagulation (DIC)
        Cerebral oedema/hernia
    3. Invade neighbouring cells to form abcess and evade immune system - rarely enter blood stream
Typhoid Fever vs Salmonellosis
1. Salmonella
  1. Caused by Salmonella enterica
  2. Treatment involves oral rehydration
  3. Causes nausea and diarrhoea
  4. Infection
    1. Bacteria enters intestinal epithelial cell
      1. Multiplies within vesicle of cell
        Multiplication in mucosal cells results in inflammatory response
        Diarrhoea
        Bacteria can cross epithelial membrane to enter lymphatics and blood stream
2. Typhoid fever
  1. Caused by Salmonella typhi
  2. Bacteria spread throughout body in phagocytes
  3. 1-3% of patients become chronic carriers
  4. Treated with Quinolones and Cephalosporins
  5. Causes high fever and high mortality
3. Both involve infection and endotoxins
4. Both diagnosed by isolation and serotyping
Vibrios
1. Cholera
  1. Vibrio cholera serotypes that produce cholera toxin (O:1 and O:139)
    1. Toxins cause cells to release Cl-, HCO- and water
    2. Exotoxins
  2. Causes diarrhoea and severe water loss
  3. Treated with doxycycline and rehydration
2. Non-cholera Vibrios
  1. Usually come from contaminated crustaceans or mollusks
  2. Include V. cholera subtypes (not including O:1 or O:139), V. parahaemolyticus and V. vulnificus
  3. Causes cholera-like diarrhoea but milder (V. parahaemolyticus) and rapidly spreading tissue destruction (V. vulnificus)
  4. Caused by infection, enterotoxin (V. parahaemolyticus)/siderophores (V. vulnificus)
  5. Treated with antibiotics (and rehydration for V. parahaemolyticus)
Campylobacter
1. Campylobacter jejuni
2. Causes fever, abdominal pain and diarrhoea
  1. Caused by infection
3. Found in chicken and cows' milk
Helicobacter
1. Helicobacter pylori
2. Ammonia from bacterial activity neutralises stomach HCl
  1. Causes more HCl production
    1. Leads to peptic ulcers
3. Diagnosis by urea test and and bacterial culture
4. Caused by infection
5. Treatment with antibacterials
Yersinia
1. Y. enterolytica/ Y. pseudotuberculosis
2. Symptoms
  1. Diarrhoea
  2. Abdominal pain (usually mild)
    1. May be confused with appendicitis
3. Caused by infection and endotoxins
4. Found in meat and milk
5. Diagnosed with bacterial culture and serotyping
Clostridium vs Bascillus
1. B. cereus
  1. Causes nausea, vomiting and diarrhoea
  2. Caused by intoxication
  3. Diagnosed by bacterial isolation
  4. Found in reheated rice
2. C. difficile/C. perfringens
  1. Caused by infection and exotoxin
  2. Cause diarrhoea (to colitis for C. difficile)
  3. Diagnosed by bacterial isolation/cytotoxin assay (for C. difficile)
  4. C. perfringens found in meat
  5. C. difficile caused by elimination of normal flora
  6. C. difficile treated with metronidazole
Escherichia coli
1. Bacteria attach to intestinal cells via fimbrae
2. Produces toxins
3. Cells may aggregate
4. Entertoxigenic, Enteroinvasive, Enteraggregative
  1. Cause Traveller's Diarrhoea
5. Shiga-toxin producing (STEC)
  1. Causes Shigella'like dysentery, hemorrhagic colitis and haemolyitic uremic syndrom
6. Detected by bacterial isolation
7. STEC treated with Quinolones and Cephalosporins (other treated with rehydration)

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Enterobacteriaceae and Gut Diseases

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	Created by maisie_oj about 11 years ago