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YEAR 5: MICRO > 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
Q

How is Salmonella transmitted?

A

Via infected meat products (but it can also be transmitted by pets (mainly reptiles))

26
Q

Describe the presentation of Salmonella enteritidis.

A
  • Enterocolitis - loose stools
  • Transmitted by poultry, eggs and meat
  • Self-limiting diarrhoea that is non-bloody
  • No fever
  • Bacteraemia is rare
27
Q

Describe the presentation of Salmonella typhi.

A
  • 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
Q

Which subset of patients are at increased risk of Salmonella bacteraemia?

A

Sickle cell patients

29
Q

How is Salmonella typhi treated?

A

Ceftriaxone

30
Q

What are some key microbiological features of Shigella?

A

Non-lactose fermenter

Does NOT produce hydrogen suphide

Non-motile

31
Q

Which antigens are seen on Shigella?

A

Cell wall O antigens

Polysaccharide (groups A-D)

32
Q

List some types of Shigella.

A
  • Shigella sonnei*
  • Shigella dysenteriae*
  • Shigella flexneri* (MSM)
33
Q

What is the most effective bacterial enteric pathogen and why?

A

Shigella - it has the lowest infective dose (50)

NOTE: Shigella has no animal reservoir and no carriers

34
Q

How does Shigella infection manifest?

A

Dysentry - severe diarrhoea with blood and mucus in the faeces

NOTE: Shigella produces shiga toxin

NOTE: avoid antibiotics when treating Shigella

35
Q

What are the microbiological features of Vibrio?

A

Comma-shaped

Late lactose-fermenters

Oxidase-positive

Gram-negative

36
Q

What are the different groups of Vibrio cholerae?

A
  • O1 - causes epidemics
  • Non-O1 - sporadic, non-pathogens
37
Q

What type of GI disturbance does Vibrio cholerae cause?

A

Produce water diarrhoea without inflammatory cells

Treat the losses (water and electrolytes)

38
Q

Name and describe the key features of other types of Vibrio.

A

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
Q

What are the main microbiological features of Campylobacter?

A
  • Comma-shaped
  • Microaerobphilic
  • Oxidase-positive
  • Gram-negative
  • Motile
40
Q

Descrie the presentation of Campylobacter jejuni infection.

A

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
Q

How is Campylobacter infection treated?

A

Only treated if immunocompromised

Erythromycin or ciprofloxacin

42
Q

What are some complications of Campylobacter infection?

A

Guillian-Barre syndrome

Reactive arthritis

43
Q

Which other bacterial organisms can cause GI disease?

A
  • Yersinia enterocolitica - non-lactose fermenter that causes enterocolitis of mesenteric adenitis (also associated with reactive arthritis)
  • Mycobacteria
44
Q

What are the key microbiological features of Entamoeba histolytica?

A
  • Motile trophozoite in diarrhoeal illness
  • Non-motile cyst in non-diarrhoeal illness
  • Killed by boiling
  • Contains four nuclei
  • No animal reservoir
45
Q

Describe the pathophysiology of diarrhoeal illness caused by Entamoeba histolytica.

A

Ingestion of cysts → trophozoites move into the ileum → colonise the colon → causes flask-shaped ulcers

46
Q

Describe the presentation of GI infection by Entamoeba histolytica.

A
  • Dysentry
  • Flatulence
  • Tenesmus
  • Liver abscess
47
Q

How is Entamoeba histolytica infection diagnosed and treated?

A
  • Diagnosis: stool microscopy, serology of invasive disease
  • Treatment: metronidazole + paromomycin
48
Q

What are the key microbiological features of Giardia lamblia?

A
  • Pear-shaped trophozoites
  • Two nuclei
  • Four flagellae and a suction disc
49
Q

Outline the pathophysiology of GI disease caused by Giardia.

A
  • 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
Q

how is Giardia infection diagnosed and treated?

A
  • Stool microscopy
  • ELISA
  • String test
  • Treatment: metronidazole
51
Q

What are the main features of Cryptosporidium parvum?

A
  • 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
Q

What is the predominant strain of norovirus?

A

GII4

53
Q

What is rotavirus and what does it cause?

A
  • 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
Q

List some other viruses that can cause diarrhoeal illnesses.

A
  • Adenovirus (types 40 and 41 can cause non-bloody diarrhoea in <2 year olds)
  • Poliovirus
  • Enterovirus (e.g. coxaskie, echovirus)
  • Hepatitis A
55
Q

Which causes of diarrhoeal illness have available vaccines?

A
  • Cholera (serogroup O1)
  • Campylobacter
  • ETEC
  • Salmonella typhi
  • Rotavirus (rotarix (live, monovalent), rotateq (pentavalent), rotashield (used if risk of intussusception))
56
Q

Who is responsible for collecting reports of diarrhoeal illness and identifying outbreaks?

A

Health Protection Unit (HPU)

YEAR 5: MICRO (24 decks)

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