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YEAR 5: Microbiology and Infection AS > MI: GI infections > Flashcards

MI: GI infections Flashcards

1
Q

List some reportable GI infections

A
  • Camplybacter
  • Salmonella
  • Shigella
  • Escherichia coli O157
  • Listeria
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2
Q

What are the main characteristics of secretory diarrhoea?

A

Watery diarrhoea (no inflammatory cells in stool)

No fever

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3
Q

What are the main characteristics of inflammatory diarrhoea?

A

Fever

Diarrhoea (inflammatory cells present, may be bloody)

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4
Q

List some examples of severe GI infections that produce a fever with little stool changes.

A
  • Salmonella typhi
  • Enteropathogenic Yersinia
  • Brucella
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5
Q

Describe the mechanism by which Vibrio cholerae causes secretory diarrhoea.

A
  • The cholera toxin has subunits A and B which stimulate adenylate cyclase.
  • This leads to the production of cAMP which opens chloride channels on the membranes of enterocytes.
  • Chloride efflux into the lumen is accompanied by water and electrolyte loss.
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6
Q

What are superantigens?

A

Toxins that bind to TCR outside the peptide binding region.
They cause large scale activation of T cells leading to massive cytokine production by CD4 cells.

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7
Q

What type of organism is Staphylococcus aureus?

A

Catalase and coagulase positive, Gram-positive coccus that appears in clusters

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8
Q

What type of toxin is produced by Staphylococcus aureus?

A

Enterotoxin - this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2

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9
Q

How is Staphylococcus aureus spread and what kind of GI symptoms can it cause?

A

Spread by skin lesions on food handlers

Causes prominent vomiting and watery, non-bloody diarrhoea

NOTE: it is self-limiting so does not require treatment

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10
Q

What type of organisms is Bacillus cereus?

A

Gram-positive rods that are spore-forming

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11
Q

What type of toxins does B. cereus produce?

A
  • Heat stable emetic toxin
  • Heat labile diarrhoeal toxin
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12
Q

What type of GI symptoms does B. cereus cause?

A

Watery, non-bloody diarrhoea

NOTE: it can cause bacteraemia and cerebral abscesses in vulnerable populations

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13
Q

Name three types of Clostridium infection and describe the diseases that they cause.

A

Clostridium botulinum - causes botulism

  • From canned food
  • Causes disease due to preformed toxin which blocks acetylcholine release at peripheral nerve synapses resulting in paralysis
  • Treated with antitoxin

Clostridium perfringens - food poisoning

  • From reheated food
  • Generates a superantigen that mainly affects the colon
  • Causes watery diarrhoea and cramps that last 24 hours

Clostridium difficile - pseudomembranous colitis

  • Hospital-acquired infection related to antibiotic use
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14
Q

Which antibiotics are most commonly implicated in C. difficile colitis?

A
  • Cephalosporins
  • Clindamycin
  • Ciprofloxacin
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15
Q

How is C. difficile colitis treated?

A
  1. Metronidazole
  2. Vancomycin
  3. Stop the offending antibiotic
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16
Q

What type of organism is Listeria monocytogenes?

A

Gram positive, rod-shaped, facultative anaerobe

Beta-haemolytic, aesculin-positive with tumbling motility

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17
Q

What GI symptoms does Listeria tend to cause?

A

Watery diarrhoea, cramps, headache, fever and a little vomiting

NOTE: it comes from refrigerated food (e.g. unpasteurised dairy)

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18
Q

How is Listeria infection treated?

A

Ampicillin

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19
Q

What type of organisms are Enterobacteriaceae?

A
  • Facultative anaerobes
  • Lactose fermenters
  • Oxidase-negative
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20
Q

Name and describe the different types of E. coli infection.

A
  • ETEC - toxigenic, main cause of travellers’ diarrhoea
  • EPEC - pathogenic, infantile diarrhoea
  • EIEC - invasive, dysentry
  • EHEC - haemorrhagic, caused by E. coli 0157:H7
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21
Q

What causes haemolytic uraemic syndrome?

A

EHEC shiga-like verocytotoxin

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22
Q

What type of bacteria are Salmonellae?

A

Non-lactose fermenting, Gram-negatives

Produce hydrogen suphide (form black colonies)

Grows on TSI agar, XLD agar and selenite F broth

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23
Q

Which antigens are found on Salmonellae?

A
  • Cell wall O (groups A-I)
  • Flagellar H
  • Capular Vi (virulence, antiphagocytic)

NOTE: differences in these antigens help identify types of Salmonellae

24
Q

List three species of Salmonella.

A
  • Salmonella typhi (and paratyphi)
  • Salmonella enteritidis
  • Salmonella choleraesuis
25
How is *Salmonella* transmitted?
Via infected meat products (but it can also be transmitted by pets (mainly reptiles))
26
Describe the presentation of *Salmonella enteritidis.*
* Enterocolitis - loose stools * Transmitted by poultry, eggs and meat * Self-limiting diarrhoea that is non-bloody * No fever * Bacteraemia is rare
27
Describe the presentation of *Salmonella typhi.*
* Transmitted only by humans * Multiplies in Peyer's patches and spreads via the endoreticular system * Slow onset fever and _constipation_ * May cause splenomegaly, rose spots, anaemia and leucopaenia * Blood cultures may be positive
28
Which subset of patients are at increased risk of *Salmonella bacteraemia?*
Sickle cell patients
29
How is *Salmonella typhi* treated?
Ceftriaxone
30
What are some key microbiological features of *Shigella?*
Non-lactose fermenter Does NOT produce hydrogen suphide Non-motile
31
Which antigens are seen on *Shigella?*
Cell wall O antigens Polysaccharide (groups A-D)
32
List some types of *Shigella.*
* Shigella sonnei* * Shigella dysenteriae* * Shigella flexneri* (MSM)
33
What is the most effective bacterial enteric pathogen and why?
*Shigella* - it has the lowest infective dose (50) NOTE: Shigella has no animal reservoir and no carriers
34
How does *Shigella* infection manifest?
Dysentry - severe diarrhoea with blood and mucus in the faeces NOTE: *Shigella* produces shiga toxin NOTE: avoid antibiotics when treating *Shigella*
35
What are the microbiological features of *Vibrio?*
Comma-shaped Late lactose-fermenters Oxidase-positive Gram-negative
36
What are the different groups of *Vibrio cholerae?*
* O1 - causes epidemics * Non-O1 - sporadic, non-pathogens
37
What type of GI disturbance does *Vibrio cholerae* cause?
Produce water diarrhoea without inflammatory cells Treat the losses (water and electrolytes)
38
Name and describe the key features of other types of *Vibrio.*
***Vibrio parahaemolyticus:*** * Caused by ingestion of raw/undercooked seafood * Causes self-limiting diarrhoea * Grows on salty agar ***Vibrio vulnificus:*** * Causes cellulitis in shellfish handlers * Can cause fatal septicaemia with D&V in HIV patients, treated with doxycycline
39
What are the main microbiological features of *Campylobacter?*
* Comma-shaped * Microaerobphilic * Oxidase-positive * Gram-negative * Motile
40
Descrie the presentation of *Campylobacter jejuni* infection.
Watery, foul-smelling diarrhoea, blood stools, fever and severe abdominal pain NOTE: transmitted by food and water that has been contaminated by animal faeces
41
How is *Campylobacter* infection treated?
Only treated if immunocompromised Erythromycin or ciprofloxacin
42
What are some complications of *Campylobacter* infection?
Guillian-Barre syndrome Reactive arthritis
43
Which other bacterial organisms can cause GI disease?
* *Yersinia enterocolitica* - non-lactose fermenter that causes enterocolitis of mesenteric adenitis (also associated with reactive arthritis) * *Mycobacteria*
44
What are the key microbiological features of *Entamoeba histolytica?*
* Motile trophozoite in diarrhoeal illness * Non-motile cyst in non-diarrhoeal illness * Killed by boiling * Contains four nuclei * No animal reservoir
45
Describe the pathophysiology of diarrhoeal illness caused by *Entamoeba histolytica.*
Ingestion of cysts → trophozoites move into the ileum → colonise the colon → causes flask-shaped ulcers
46
Describe the presentation of GI infection by *Entamoeba histolytica.*
* Dysentry * Flatulence * Tenesmus * Liver abscess
47
How is *Entamoeba histolytica* infection diagnosed and treated?
* Diagnosis: stool microscopy, serology of invasive disease * Treatment: metronidazole + paromomycin
48
What are the key microbiological features of *Giardia lamblia?*
* Pear-shaped trophozoites * Two nuclei * Four flagellae and a suction disc
49
Outline the pathophysiology of GI disease caused by *Giardia.*
* Transmitted by ingestion of cyst from faecally contaminated water * Excystation in the duodenum leads to trophozoite attachment * Results in malabsorption of protein and fat * Presentation: foul-smelling non-bloody diarrhoea, cramps, flatulence, NO fever
50
how is *Giardia* infection diagnosed and treated?
* Stool microscopy * ELISA * String test * Treatment: metronidazole
51
What are the main features of *Cryptosporidium parvum?*
* Causes severe diarrhoea in the immunocompromised * Oocysts can be seen in the stool using modified Kinyoung acid fast stain * Treated by boosting the immune system
52
What is the predominant strain of norovirus?
GII4
53
What is rotavirus and what does it cause?
* dsDNA * Replicates in the mucosa of the small intestine and causes secretory diarrhoea with no inflammation NOTE: exposure to natural infection twice will confer lifelong immunity
54
List some other viruses that can cause diarrhoeal illnesses.
* Adenovirus (types 40 and 41 can cause non-bloody diarrhoea in \<2 year olds) * Poliovirus * Enterovirus (e.g. coxaskie, echovirus) * Hepatitis A
55
Which causes of diarrhoeal illness have available vaccines?
* *Cholera* (serogroup O1) * *Campylobacter* * ETEC * *Salmonella typhi* * Rotavirus (rotarix (live, monovalent), rotateq (pentavalent), rotashield (used if risk of intussusception))
56
Who is responsible for collecting reports of diarrhoeal illness and identifying outbreaks?
Health Protection Unit (HPU)

YEAR 5: Microbiology and Infection AS (25 decks)

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