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PATH FINAL > Micro: GI Infections > Flashcards

Micro: GI Infections Flashcards

1
Q

Epidemiology of GI infections

A
  • Vulnerable groups: infants and elderly
  • Most are self-limiting (hence do not seek medical care)
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2
Q

Reportable GI infections

A

Most gastroenteritis cases are reportable. However these are the most important to report:
* Camplybacter
* Salmonella
* Shigella
* Escherichia coli O157
* Listeria

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3
Q

3 types of clinical syndromes associated with GI infections

A

Secretory diarrhoea
Inflammatory diarrhoea
Enteric fever

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4
Q

How can you differentiate between the different GI infections clinical syndromes

A

If main symptoms are gastroenteritis (diarrhoea, GI cramps) then check if they have a a fever:
- no fever = secretory diarrhoea
- fever = inflammatory diarrhoea

If main symptom is fever and systemically unwell with fewer GI side effects = enteric fever

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5
Q

Secretory diarrhoea:
- Pathophysiology
- Main symptoms
- Common causative pathogens

A

Pathophysiology
- Toxin production can either 1) induce cAMP in enterocytes which opens Cl- channels at apical membrane of enterocytes causing a Cl- efflux into lumen which results in watery diarrhoea and dehydration OR 2) toxin superantigen binds to T cell receptors causing massice cytokine release which causes Cl- secreted into lumen.

Symptoms
- Watery diarrhoea with NO fever
- no inflammatory cells in stool

Common causative pathogens
- Cholera
- Enterobacteriacae (ETEC, EPEC)
- Viruses (Norovirus, Adenovirus, Rotavirus)

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6
Q

Inflammatory diarrhoea:
- Pathophysiology
- Main symptoms
- Common causative pathogens

A

Pathophysiology
- inflammation AND bacteraemia which in immunocompromised patients may result in shock

Symptoms
- Bloody diarrhoea (=dysentery) with inflammatory cells in stool
- Fever

Common causative pathogens
(CHESS)
- Campylobacter
- EHEC
- Entamoeba
- Salmonella (non-typhoidal)
- Shigella

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7
Q

Enteric diarrhoea:
- Main symptoms
- Common causative pathogens

A

Main Symptoms
- Systemically unwell
- Fever
- Fewer GI symptoms

Common Causative Pathogens
- Typhoidal salmonella
- Yersinia
- Brucella

these are more severe GI infections

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8
Q

What type of organism is Staph. Aureus (4)

A

Gram positive cocci appearing in clusters
Catalase and coagulase positive
Aerobic
Yellow in agar plate

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9
Q

GI infection: Staph. Aureus
How does Staph. Aureus cause a GI infection

A

Produces enterotoxin which acts as a superantigen causing IL1/2 release

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10
Q

GI infection: Staph. Aureus
Incubation & Duration
How is it spread

A
  • VERY SHORT incubation of 2-4 hours
  • Duration of <1 day
  • Spread by skin lesions (commonly through infected food handlers)
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11
Q

GI infection: Staph. Aureus
Symptoms and Treatment

A

Symptoms
Prominent vomiting
Watery non-bloody diarrhoea
type of secretory diarrhoea

Treatment
Self-limiting

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12
Q

What type of organism is Bacilus Cereus (3)

A

Gram positive rods
Aerobe
Spore forming

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13
Q

GI infection: B. Cereus
Source of infection
Incubation & Duration period

A

Source of infection
- Reheated rice (reheating causes to germinate)

Incubation & Duration
Incubation = 1-6 hours
Duration = <1 day

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14
Q

GI infection: B. Cereus
Pathophysiology
Symptoms (and complications)
Treatment

A

Pathophysiology
- Produces toxins. Heat-stable emetic toxin (not destroyed upon reheating) and heat-labile diarrhoeal toxin(destroyed in reheating, but present in improper heating of food)

Symptoms
Vomiting and non-bloody watery diarrhoea
May cause bacteraemia and cerebral abscesses in vulnerable populations

Treatment
Self-limiting

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15
Q

What type of organism is Clostridium
What are the different types of Clostridium

A

Gram positive rod + anaerobe

Types
- Clostridium Botulinum
- Clostridium Perfringens
- Clostridium Difficile

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16
Q

GI infections: Clostridium
Differentiate between the different types of Clostridium infections

A

Clostridium botulinum - causes botulism

  • From canned food and packed food (honey, beans)
  • Causes disease due to preformed toxin which cleaves SNARE proteins preventing acetylcholine release at peripheral nerve synapses resulting in descending paralysis (differentiate from GBS - ascending)
  • Treated with antitoxin

Clostridium perfringens - food poisoning

  • From reheated food (8-16hr incubation)
  • Generates a superantigen that mainly affects the colon
  • Causes watery diarrhoea and cramps that last 24 hours
  • Complication: gas gangrene

Clostridium difficile - pseudomembranous colitis

  • Hospital-acquired infection related to antibiotic use (4C’s: cephalosproins, Ciprofloxacin, Clindamycin, Co-Amoxiclav)
  • Has 2 exotoxins (A, B)
  • Treatment: 1) stop offending abx 1) Vancomycin (second line=fidaxomicin)
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17
Q

What type of organism is Listeria (3)

A

Gram positive rod
Beta-haemolytic, aesculin-positive
Motile

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18
Q

GI infection: Listeria Monocytogenes
Source of infection

A

Refrigerated food (sandwich, veggies)
Unpasteurised dairy (monocyto-cheese!)
Often causing an outbreak of febrile gastroenteritis

19
Q

GI infection: Listeria Monocytogenes
Symptoms
Treatment

A

Symptoms
- Fever + watery diarrhoea
- Headache
- Little vomiting
- most vulnerable groups = perinatal infection (may result in stillbirth) and immunocompromised pts

Treatment
- Ampicillin

20
Q

What are the gram positive bacteria which may cause a GI infection

A

Staph A (cocci + clusters)
Bacillus Cereus (rods + aerobic + spore forming)
Clostridium (rods + anaerobic)
Listeria (rods + beta haemolytic + motile)

21
Q

What type of organisms are Enterobacteriaceae (4)

A
  • Gram negative
  • Faculative anaerobe (makes ATP if O2 present but can undergo fermentation in anaerobic environments)
  • Lactose fermenters
  • Oxidase-negatieve
22
Q

GI infection: E.Coli
Differentiate between the different types of infection

A

ETEC
- Toxigenic
- Main cause of travellers’ diarrhoea

EPEC
- Pathogenic
- Infantile diarrhoea

EIEC
- Invasive
- Dysentry

EHEC
- Haemorrhagic
- Caused by E. coli 0157:H7
- May result in haemolytic uraemic syndrome (due to shiga-like vierocytotoxin)
- Dysentery + MAHA + Renal failure
- Incubation of 1-5 days and duration 1-4 days

NOTE: ALL are spread through faecal-oral route

23
Q

GI infection: E.Coli
Treatment

A

Self-limiting
Avoid abx - thought to exacerbate condition

24
Q

What type of organisms are Salmonella (4)

A
  • Gram negatives
  • Non-lactose fermenting
  • Produce hydrogen sulphide (forming black colonies)
  • Motile
25
Q

How can you differentiate the different types of Salmonellae?

A

Difference in antigens found on bacterium

  • Cell wall O (groups A-I)
  • Flagellar H
  • Capular Vi (virulence, antiphagocytic)
26
Q

List two species of Salmonella.

A
  • Salmonella typhi (and paratyphi)
  • Salmonella enteritidis
27
Q

GI infection: Salmonella Enteritidis and Typhi
Differentiate between the two types of Salmonella infection

A

Salmonella Enteritidis
- invasion of epi and sub epithelial tissue of small and large bowel causing entercolitis
- non-bloody diarrhoea (stool +ve cultures)
- 12-48hr incubation period
- No fever and bacteriaemia is rare
- Transmitted by poultry, eggs, meat, reptile pets

Salmonella Typhi
- Transmitted only by humans
- Multiples in Peyer’s patches and spreads via endoretircular system (resulting in bacteraemia - +ve blood cultures)
- Sx = Slow onset fever and constipation + splenomegaly + rose spots + anaemia + leucopaenia (fever in returning traveller!)

28
Q

GI infection: Salmonella Enteritidis and Typhi
Treatment

A

Salmonella Enteritidis = self-limiting
Salmonella typhi = IV ceftriaxone then PO azithromycin

29
Q

What type of organism is Shigella (4)

A
  • Gram negative
  • Non-lactose fermenter
  • Does NOT produce hydrogen suphide
  • Non-motile
30
Q

GI infection: Shigella
Pathophysiology

A
  • Produces shiga toxin affecting teh distal ileum and colon resulting in mucosal inflammation
  • Highly infectious (very small infective dose - lowest of GI infections!!!) hence behind many outbreaks

Incubation of 12-96 hours with Duration of 5-7 days

31
Q

GI infection: Shigella
Symptoms
Treatment

A

Symptoms
- Dysentery (severe diarrhoea with blood and mucus)
- Fever
- Abdominal pain

Treatment
- Self-limiting
- Try to avoid abx but Ciprofloxacin can be given if needed

32
Q

What type of organism is Vibrio

A

Gram negative
Comma-shaped
Late lactose-fermenters
Oxidase-positive

33
Q

GI infection: Vibrio Cholera
Pathophysiology

A

Colonisation of small bowel, where enterotoxin stimulates cAMP resulting in opening of Cl- channels and Cl- efflux out of cells. This results in Na+ moving out and water following by osmosis ==> severe dehydration!

Transmitted by human faeces in contaminated water (especially in water borne food - rice, shellfish)

34
Q

GI infection: Vibrio Cholera
Symptoms and treatment

A

Symptoms
Rice water stool - watery diarrhoea without inflammatory cells

Treatment
Self-limiting

35
Q

GI infection: Vibrio
Outliune the key features of other types of vibirio (excluding cholera)

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

Both self-limiting

36
Q

What type of organism is Campylobacter

A
  • Gram negative s-shaped rod
  • Oxidase-positive
  • Grows at 42 degrees C
  • Motile
37
Q

GI infections: Campylobacter
Spread
Symptoms

A

Spread
Undercooked Poultry
BBQ!!!!

Symptoms
* Prodrome of fever and headahce
* Followed by abdominal cramps
* Bloody diarrhoea
* Lasts for 2-20 days

38
Q

GI infections: Campylobacter
Treatment
Complications

A

Treatment
- Erithromycin or Cirpo if in first 5 days
- Otherwise after self-limiting - only treat if immunocompromised

Complications
- GBS
- Reactive arthritis

39
Q

GI infections: Yersinia Enterocolitica
Key features

A

Sources: undercooked pork

Symptoms
- Fever, abdo pain, diarrhoea
- (presentation may be like appendicitis)
- Associated with reactive arthritis

40
Q

What gram negative bacteria can cause GI infections

A
  • Enterobacteriaceae (lactose fermenters, oxidase negative)
  • Salmonella (non-lactose, H2S producers, motile)
  • Shigella (non-lactose, non-H2S, non-motile)
  • Vibrio (comma-shaped, late lactose, oxidase positive)
  • Campylobacter (s-shaped/comma, lactose, oxidase, 42C, motile)
  • Yersinia E.
41
Q

Protozoa which may cause GI infections & Key features

A

Entamoeba Histolytica
- Flask-shaped ulcer in colon (seen on histology)
- Sx: dystentery + flatulence + tenesmus
- common in MSM
- Dx: stool micro and serology
- Complications: chronic infection may lead to liver abscess (RUQ pain, weightloss, fevers)
- Rx: Metronidazole + Dantomyocin

Giardia Lamblia
- commonest protozoa GI infection
- Pear-shaped trophozoite with 2 nuclei and 4 flagellae
- Risk factors: travellers from South-East Asia
- Spread from contaminated water + food
- Sx: foul-smelling non-blood diarrhoea (as causes malabsorption of fat and protein) + lots of cramps + NO fevers
- Dx: stool micro + ELISA
- Rx: Metronidazole

42
Q

Differentiate between viruses which may cause GI infections & Key features

A

Norovirus
- GII.4 is the commonest strain
- Adult outbreak of secretory diarrhoea (has low infectious dose)

Adenovirus
- Secretory diarrhoea in <2yo or Immunosuppressed

Rotavirus
- dsDNA affecting mucosa of small intestine
- Nursery outbreaks (<6yo)
- most children by age of 6 will have abs to at least 2 type - recurrent infection eventually leads to life long immunity

43
Q

Prevention measures against GI infections

A
  • Handwashing!!!!!!
  • Food washing
  • Vaccination
44
Q

Which causes of GI infections have available vaccines

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

PATH FINAL (36 decks)

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