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Week 7 - Clinical Microbiology & Infections 2 > GI Infections > Flashcards

GI Infections Flashcards

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1
Q

Define gastroenteritis [1]

A

inflammation of the stomach and intestinal epithelium

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2
Q

What are the symptoms of gastroenteritis? [4]

A
  1. nausea
  2. vomiting
  3. diarrhoea
  4. abdominal discomfort
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3
Q

Define diarrhoea [1]

A

disease of the small intestine involving increased fluid and electrolyte loss

  • frequent and/or fluid stool, at least 3 episodes/day
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4
Q

Define dysentery [1]

A

inflammatory disorder of the large intestine

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5
Q

What are the symptoms of dysentery? [3]

A
  1. blood and pus in the stool
  2. abdominal pain
  3. fever
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6
Q

Define enterocolitis [1]

A

inflammation involving the mucosa of both small and large intestine

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7
Q

There are 7 types of diarrhoea according to the Bristol Stool Chart. Describe Type 1 diarrhoea [2]

A
  1. separate hard lumps, like nuts
  2. hard to pass
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8
Q

There are 7 types of diarrhoea according to the Bristol Stool Chart. Describe Type 2 diarrhoea [2]

A
  1. sausage-shaped
  2. lumpy
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9
Q

There are 7 types of diarrhoea according to the Bristol Stool Chart. Describe Type 3 diarrhoea [2]

A
  1. sausage-shaped
  2. with cracks on the surface
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10
Q

There are 7 types of diarrhoea according to the Bristol Stool Chart. Describe Type 4 diarrhoea [2]

A
  1. like sausage or snake
  2. smooth and soft
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11
Q

There are 7 types of diarrhoea according to the Bristol Stool Chart. Describe Type 5​ diarrhoea [3]

A
  1. soft blobs
  2. with clear cut edges
  3. easy to pass
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12
Q

There are 7 types of diarrhoea according to the Bristol Stool Chart. Describe Type 6​ diarrhoea [3]

A
  1. fluffy pieces
  2. with ragged edges
  3. a mushy stool
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13
Q

There are 7 types of diarrhoea according to the Bristol Stool Chart. Describe Type 7 diarrhoea [3]

A
  1. watery
  2. no solid pieces
  3. entirely liquid
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14
Q

How can GI infection manifest within the GI tract? [4]

A
  1. Toxin effects
    • e.g. cholera
  2. Inflammation due to microbial invasion
    • e.g. shigellosis
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15
Q

How can GI infection manifest outwith the GI tract? [4]

A
  1. Systemic effect of toxins
    • e.g. STEC
  2. Invasive infection of GIT with wider dissemination
    • e.g. metastatic salmonella infection
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16
Q

What are the normal barriers to GI infection in the mouth? [1]

A

lysozyme

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17
Q

What are the normal barriers to GI infection in the stomach? [1]

A

acidic pH

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18
Q

What are the normal barriers to GI infection in the small intestine? [6]

A
  1. Mucous
  2. Bile
  3. Secretory lgA
  4. Lymphoid tissue (Peyer’s patches)
  5. Epithelial turnover
  6. Normal flora
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19
Q

What are the normal barriers to GI infection in the large intestine? [2]

A
  1. epithelial turnover
  2. normal flora
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20
Q

What are the functions of normal gut flora? [2]

A
  1. protective function
  2. metabolic function
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21
Q

Many GI infections are zoonotic. What does this mean? [1]

A

zoonotic infections are infectious diseases caused by bacteria, viruses and parasites that spread between animals (usually vertebrates) and humans

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22
Q

What is the typical reservoir for E. coli? [1]

A

animal reservoir

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23
Q

What is the typical reservoir for EHEC (Enterohemorrhagic E. coli)? [1]

A

food-borne

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24
Q

What is the typical reservoir for ETEC (enterotoxigenic E.coli)? [1]

A

water-borne

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25
Q

What is the typical reservoir for salmonella? [3]

A
  1. mostly food-borne
  2. small prevalence in animal reservoirs/water-borne
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26
Q

What is the typical reservoir for campylobacter? [3]

A
  1. mostly food-borne
  2. small prevalence in animal reservoirs/water-borne
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27
Q

What is the typical reservoir for vibrio cholerae? [2]

A
  1. mostly water-borne
  2. small prevalence in food
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28
Q

What is the typical reservoir for shigella? [1]

A

food-borne

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29
Q

What is the typical reservoir for clostridium perfringens? [2]

A
  1. mostly food-borne
  2. small prevalence in water
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30
Q

What is the typical reservoir for bacillus cereus? [1]

A

food-borne

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31
Q

What is the typical reservoir for vibrio parahaemolyticus? [1]

A

food-borne

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32
Q

What are the typical reservoirs for listeria monocytogenes? [2]

A
  1. food-borne
  2. animal reservoir
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33
Q

What is the typical reservoir for yersinia enterocolitica? [2]

A
  1. food-borne
  2. animal reservoir
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34
Q

What are the 3 methods of transmission of GI infections? (the 3 F’s)? [3]

A
  1. Food
    • Contamination — Farm to fork
    • Cross-contamination — Distribution chain or domestic kitchen
  2. Fluids
    • Water
    • Contaminated juices etc.
  3. Fingers
    • ​​Importance of washing hands
      • After toileting
      • Before and/after preparing or consuming food and drinks
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35
Q

What things should you gather in a history of a patient with a suspected GI infection? [5]

A
  1. nature of diarrhoea
  2. timing (acute vs chronic)
  3. food history (?outbreak),
  4. recent antibiotic usage
  5. foreign travel
36
Q

What are the typical features you see on examination of a patient with a suspected GI infection? [5]

A
  1. febrile (feverish)
  2. shock
  3. systemically unwell
  4. wasting
  5. neurological signs
37
Q

What investigations should you order to diagnose a patient with a suspected GI infection? [3]

A
  1. blood tests (FBC, U&E, blood film)
  2. sigmoidoscopy
  3. abdominal x-ray/CT
38
Q

Describe the approaches used in the lab in order to diagnose a particular GI infection [3]

A
  1. Enrichment broth
    • Contains nutrients that promote preferential growth of the pathogen
  2. Selective media
    • Suppress growth of background flora while allowing growth of the pathogen
  3. Differential media
    • Distinguishes mixed microorganisms on the same plate by biochemical characteristics of microorganisms growing in presence of specific nutrients combined with an indicator that changes colour (e.g. E.coli turns pink vs. Shigella is colourless)
39
Q

How should GI infections be treated? [3]

A
  1. Most mild bacterial GI infections resolve spontaneously
  2. Maintenance hydration is crucial & can be life-saving
  3. Antibiotics are not usually used
    • antibiotic treatment is mostly reserved for severe/prolonged symptoms - due to risks associated with its use
40
Q

What are the 3 major microbiological causes of GI infection? (The Big 3) [3]

A
  1. salmonella
  2. campylobacter
  3. E. coli
41
Q

What is the incubation period? [1]

A

the interval between exposure to an infection and the appearance of the first symptoms

42
Q

Describe the microbiological features of salmonella [2]

A
  1. gram-negative bacilli
  2. non-lactose fermenter
43
Q

Describe the pathogenesis of salmonella infection [3]

A
  1. Diarrhoea occurs due to invasion of epithelial cells in the distal small intestine, and subsequent inflammation
  2. Bacteraemia can occur in very young or elderly patients and immunocompromised patients
  3. Distant organs may become seeded to establish metastatic foci of infection, leading to:
    • osteomyelitis
    • septic arthritis
    • meningitis etc.
44
Q

How long is the incubation period for salmonella infection? [1]

A

12-72 hours

45
Q

What are the typical symptoms of salmonella infection? [3]

A
  1. Watery diarrhoea
  2. Vomiting
  3. Fever (usually associated with more invasive disease)
46
Q

How long does a salmonella infection typically last? [1]

A

2-7 days

47
Q

How do you treat a salmonella infection? [2]

A
  1. Fluid replacement is sufficient in most cases
  2. Antibiotics reserved for severe infections and bacteraemia
    • Beta-lactams, quinolones or aminoglycosides may be used
  3. However, antibiotics and antimotility agents prolong excretion of salmonellae in the faeces
48
Q

Describe the microbiological features of campylobacter [2]

A
  1. Curved Gram-negative bacilli
  2. Microaerophilic and thermophilic (42°C)
49
Q

Describe the pathogenesis of campylobacter infection [3]

A
  1. Inflammation, ulceration & bleeding in small and large bowel occurs due to bacterial invasion
  2. Bacteraemia can occur in very young or elderly patients and the immunocompromised
  3. Rarely causes post-infectious demyelination syndrome (Guillain-Barre)
    • characterised by ascending paralysis
50
Q

How long is the incubation period of campylobacter infection? [1]

A

2-5 days

51
Q

What are the typical symptoms of campylobacter infection? [2]

A
  1. bloody diarrhoea
  2. crampy abdominal pain
52
Q

How long does a campylobacter infection last? [1]

A

2-10 days

53
Q

How do you treat a campylobacter infection? [5]

  • hints:
    1. in most cases? [1]
    2. in severe/persistent disease? [2]
    3. in invasive disease? [2]
A
  1. Fluid replacement is sufficient in most cases
  2. Clarithromycin/Erythromycin for severe/persistent disease
  3. Quinolone (e.g. ciprofloxacin) or aminoglycoside (e.g. gentamicin) for invasive disease
54
Q

What type of bacteria is Escherichia coli (E. coli)? [1]

A

gram-negative bacilli

55
Q

Name the 6 diarrhoeagenic groups of E. coli [6]

A
  1. Enteropathogenic E. coli (EPEC)
  2. Enterotoxigenic E. coli (ETEC)
  3. Enterohaemorrhagic E. coli (EHEC)
  4. Enteroinvasive E.coli (EIEC)
  5. Entero-aggregative E.coli (EAEC)
  6. Diffuse aggregative E.coli (DAEC)
56
Q

What is the epidemiology of EPEC (enteropathogenic E. coli)? i.e. who typically gets it? [3]

A
  1. Sporadic cases
  2. Outbreaks of diarrhoea in infants & children
  3. Cause of some cases of traveller’s diarrhoea
57
Q

Describe the pathogenesis of EPEC infection [5]

A
  1. EPEC adhere to the epithelial via pili
  2. This causes the formation of the characteristic “attaching & effacing” lesion mediated by the intimin protein and Tir (translocated intimin receptor)
  3. This leads to a disruption of intestinal microvilli → reduced absorption capacity → watery/mucous diarrhoea
58
Q

How long is the incubation period of EPEC infection? [1]

A

1-2 days

59
Q

What are the symptoms of EPEC infection? [4]

A
  1. watery diarrhoea
  2. abdominal pain
  3. vomiting
  4. often accompanied by fever
60
Q

Who typically gets affected by ETEC (enterotoxigenic E. coli) infection? [2]

A
  1. The major bacterial cause of diarrhoea in infants & children in developing world
  2. The major cause of traveller’s diarrhoea
61
Q

Describe the pathogenesis of ETEC infection [3]

A
  • Diarrhoea due to action of 1 or 2 plasmid-encoded toxins
    1. Heat-labile (LT) toxin → structural and functional analogue of cholera toxin
    2. Heat-stable (ST) toxin → produced in addition to or instead of LT and has a similar mode of action
62
Q

How long is the incubation period of ETEC infection? [1]

A

1-7 days

63
Q

What are the symptoms of ETEC infection? [3]

A
  1. watery diarrhoea
  2. abdominal pain
  3. vomiting
64
Q

What are the symptoms of EHEC (enterohaemorrhagic E. coli) infection? [4]

A
  1. bloody diarrhoea
  2. abdominal pain
  3. vomiting
  4. haemolytic uraemic syndrome (5-10% of cases)
65
Q

What are the 3 features of haemolytic uraemic syndrome? [3]

A
  1. Microangiopathic haemolytic anaemia
  2. Thrombocytopenia
  3. Acute renal failure
66
Q

Describe the microbiological features of shigella [2]

A
  1. gram negative bacilli
  2. non-lactose fermenter
67
Q

What are the 4 species of shigella and how severe of an infection do each cause? [4]

A
  1. Shigella sonnei → associated with milder infections
  2. Shigella boydii & S.fiexneri → associated with more severe disease
  3. Shigella dysenteriae → associated with most severe disease
68
Q

Describe the pathogenesis of shigella infection [3]

A
  1. Organisms attach to and colonise mucosal epithelium of terminal ileum & colon
  2. S. dysenteriae produces a potent protein exotoxin (Shiga toxin):
    • damages intestinal epithelium
    • in some patients, it also targets glomerular endothelium causing renal failure as part of haemolytic-uraemic syndrome (HUS)
69
Q

What are the symptoms of a shigella infection? [4]

A
  1. Initially watery diarrhoea followed by bloody diarrhoea
  2. Marked, cramping abdominal pain
  3. Fever is usually present
70
Q

What are the treatment options for shigella infection? [3]

A
  1. Usually self-limiting
  2. Fluid replacement is usually sufficient
  3. Some cases of S. dysenteriae infection will require treatment of renal failure
71
Q

Describe the pathogenesis of vibrio cholerae [3]

A
  1. Flagellae and mucinase facilitate penetration of intestinal mucosa
  2. Attachment to mucosa by specific receptors
  3. Diarrhoea due to production of a potent protein exotoxin
72
Q

What are the typical presenting features of vibrio cholerae infection? [6]

A
  1. Severe profuse, non-bloody, watery diarrhoea
    • (rice water stool)
  2. Profound fluid loss & dehydration precipitates:
    • hypokalemia,
    • metabolic acidosis,
    • hypovolemic shock
    • cardiac failure
73
Q

How do you treat vibrio cholerae infection? [2]

A
  1. prompt oral or intravenous rehydration is lifesaving
  2. tetracycline antibiotics may shorten duration of shedding
74
Q

What are the 2 typical pathogens that cause food poisoning? [2]

A
  1. Bacillus cereus
  2. Staphylococcus aureus
75
Q

What are the typical features of food poisoning by staphylococcus aureus? [5]

A
  1. Profuse vomiting and abdominal cramps
  2. No fever and no diarrhoea
  3. Duration 12 - 24 hours
76
Q

Describe the features of the 2 types of diseases that results from food poisoning by bacillus cereus [8]

A
  1. Emetic disease
    • typically associated with fried rice
    • spores survive initial boiling
    • protein enterotoxin produced during sporulation
      • heat stable toxin survives further frying
  2. Diarrhoeal disease
    • spores in food survive cooking, germinate and organisms multiply in food
    • ingested organisms produce a heat-labile toxin in the gut with similar mode of action to cholera toxin
77
Q

What are the presenting features of emetic disease vs. diarrhoeal disease by bacillus cereus (and how do you differentiate between the two)? [8]

A
  1. Emetic Disease
    • profuse vomiting
    • abdominal cramps
    • watery diarrhoea
    • no fever
  2. Diarrhoeal disease
    • watery diarrhoea
    • abdominal cramps
    • no vomiting
    • no fever
78
Q

What are the typical presenting symptoms of clostridium perfringens infection? [4]

A
  1. watery diarrhoea
  2. abdominal cramps
  3. no fever
  4. no vomiting
79
Q

Describe the pathogenesis and presenting features of clostridium botulinum [5]

A
  1. Absorbed toxins spread via bloodstream and enter peripheral nerves where they cause neuromuscular blockade at the synapses
    • neuromuscular blockade results in:
      • flaccid paralysis
      • progressive muscle weakness
  2. involvement of muscles of chest/diaphragm causes
    • respiratory failure
80
Q

What are the treatment options for clostridium botulinum infection? [2]

A
  1. Urgent intensive supportive care due to difficulties breathing and swallowing
  2. Antitoxin
81
Q

What are the clinical presentation of clostridium difficile infection? [5]

A
  1. Mild to severe with abdominal pain
  2. Severe cases may develop pseudomembranous colitis
  3. Fulminant cases may progress to colonic dilatation and perforation
  4. Severe cases may be fatal
  5. Relapses are common and may be multiple
82
Q

What are the treatment options for clostridium difficile infection? [4]

A
  1. Stop precipitating antibiotics
  2. Oral metronidazole (mild [0 severity markers]).
  3. Oral vancomycin (severe [>1 severity markers or no improvement after 5 days metronidazole])
  4. Refractory recurrent disease may require faecal transplant
83
Q

How does listeria monocytogenes infection typically present? [4]

A
  1. Initial flu-like illness, with or without diarrhoea
  2. Majority of cases present with severe systemic infection
    • Septicemia
    • Meningitis
84
Q

How is listeria monocytogenes infection treated? [2]

A

Intravenous antibiotics (usually Ampicillin and synergistic gentamicin) is required

85
Q

What are the potential complications of H. pylori? [3]

A
  1. peptic ulcers
  2. duodenal ulcers
  3. increased risk of gastric cancer
86
Q

How do you treat H. pylori infection? [2]

A

Combined treatment with a proton pump inhibitor and combinations of antibiotics such as clarithromycin and metronidazole eradicates carriage and facilitates ulcer healing

87
Q

What factors increase potential for new pathogens to emerge? [10]

A
  1. Pathogenicity determinants often on mobile genetic elements
    • Bacteriophages
    • Plasmids
    • Transposons
  2. Pathogenicity traits often grouped together in large integrons or pathogenicity islands
  3. Frequently also contain antibiotic resistance genes
    • Refractory to treatment
    • Selective advantage
  4. Many of the pathogens have evolved from gut flora
  5. Existing pathogens can acquire new pathogenicity traits

Week 7 - Clinical Microbiology & Infections 2 (16 decks)

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