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Week 7 - microbiology > Bacterial GI infections > Flashcards

Bacterial GI infections Flashcards

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1
Q

What is the definition of gastroenteritis?

A

A syndrome characterised by GI symptoms including nausea, vomiting, diarrhoea, abdominal discomfort

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2
Q

What is the definition of diarrhoea?

A

Frequent and/or fluid stool, at least 3 episodes a day

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3
Q

What is the definition of dysentery?

A

Blood and pus in the stools, usually with abdominal pain and fever

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4
Q

What is the definition of enterocolitis?

A

Inflammation involving mucosa of both the small and large intestine

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5
Q

What are the manifestations of GI infection within the GI tract?

A
  • Toxin effects e.g. cholera

* Inflammation due to microbial invasion e.g. shigellosis

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6
Q

What are the manifestations of GI infection outwith the GI tract?

A
  • Systemic effect of toxins e.g. STEC

* Invasive infection of GI tract with wider dissemination e.g. metastatic salmonella

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7
Q

What are the barriers to GI infection in the mouth?

A

Lysozyme

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8
Q

What are the barriers to GI infection in the stomach?

A

Acidic pH

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9
Q

What are the barriers to GI infection in the small intestine?

A
  • Mucous
  • Bile
  • Secretory IgA
  • Lymphoid patches (Peyer’s patches)
  • Epithelial turnover
  • Normal flora
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10
Q

What are the barriers to GI infection in the large intestine?

A
  • Epithelial turnover

* Normal flora

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11
Q

What are 99% of the normal GIT flora?

A

Anaerobes

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12
Q

What is the function of the normal gut flora?

A

It has a metabolic and protective function

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13
Q

What are the sources of GI infection?

A
  • Zoonotic from symptomatic animals or asymptomatic shedders
  • Human carriers e.g. typhoid
  • Envrionmental sources e.g. contamination of soil
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14
Q

What is faecal oral transmission?

A

Any means by which infectious organisms from human/animal faeces can gain access to the GIT of another susceptible host

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15
Q

What are the 3 Fs of transmission of GI infection?

A 
•Food 
 - contamination 'farm to fork'
 - cross contamination from distribution chain or domestic 
•Fluids 
 - water 
 - contaminated juices etc. 
•fingers 
 - importance of washing hands
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16
Q

In someone presenting with GI infection, what should be asked about in a history?

A
  • nature of the diarrhoea
  • Timing - acute vs chronic
  • Food history (has there been a recent outbreak?)
  • Recent antibiotic use
  • Foreign travel
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17
Q

In someone presenting with a GI infection, what investigations should be carried out?

A 
•Blood tests:
 - FBC 
 - U+Es 
 - blood film 
•sigmoidoscopy 
•Abdo x-ray/CT
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18
Q

Describe the laboratory diagnosis of GI infection

A
  • Enrichment broth (nutrients promoting growth of pathogen)
  • Selective media (suppresses growth of background flora)
  • Differential media (distinguishes mixed micro-organisms on the same plate)
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19
Q

Explain what MacConkey’s agar is

A
  • Differential media
  • Lactose fermenting colonies are pink
  • non-lactose fermenting colonies are colourless
  • Can be made more selective by adding bile salts
  • Can be used to differentiate between E.Coli (pink) and shigella (colourless)
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20
Q

Describe control of GI infections in the public

A
  • Adequate public health measures
  • Safe clean drinking water and proper sewage disposal
  • Education in hygienic food preparation, hand hygiene, preventing cross contamination and properly cooking food
  • Pasteurisation of milk and dairy products
  • Sensible travel food practices (wash it, peel it, cook it or forget it)
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21
Q

What are the 3 main bacteria causing GI infection?

A
  • Salmonella
  • Campylobacter
  • E coli
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22
Q

Describe the appearance of salmonella

A

Gram negative bacilli

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23
Q

How are serotypes of salmonella distinguished from each other?

A
  • Lipopolysaccharide ‘o’ antigens on the cell wall

* Flagellar protein ‘H’ antigens

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24
Q

Describe the transmission of salmonella

A
  • Contaminated food, especially pork, poultry and other meat/dairy products
  • waterborne less common
  • Secondary spread person-person may occur
25
Q

When are the seasonal peaks of salmonella?

A

Summer and autumn

26
Q

Describe the appearance of salmonella on an XL D plate

A

Black colonies

27
Q

What is the pathogenesis of salmonella?

A
  • Diarrhoea due to the invasion of epithelial cells in the distal small intestine and subsequent inflammation
  • Bacteraemia can occur (extremes of age, immunocompromised)
  • Distant organisms may become seeded to establish metatatic foci of infection e.g. osteomyelitis, septic arthritis, meningitis etc.
28
Q

What is the incubation period of salmonella?

A

12-72 hours

29
Q

What are the symptoms of salmonella?

A
  • Watery diarrhoea
  • Vomiting is common
  • Fever can occur but is usually associated with more invasive disease
30
Q

What is the duration of salmonella infection

A

2-7 days

31
Q

What is the treatment of salmonella?

A
  • Fluid replacement is sufficient in most cases
  • Antibiotics are reserved for severe infections or bacteraemia (beta lactams, quinolones or ahminoglycosides may be used) but both antibiotics and anti motility agents will prolong the excretion of salmonella in the faeces
32
Q

What is the appearance of campylobacter?

A

Curved gram negative bacilli

33
Q

How is campylobacter grown?

A

Campylobacter selective agar

34
Q

What is the most important campylobacter species?

A

C. jejuni

35
Q

Describe the transmission of campylobacter

A
  • Large animal reservoir
  • Transmission occurs via contaminated food, milk or water
  • Person to person spread is rare
36
Q

What is the pathogenesis of campylobacter?

A
  • Inflammation, ulceration and bleeding in small and large bowel due to bacterial invasion
  • Bacteraemia can occur (extremes of age, immunocompromised)
  • Rarely causes post infectious demyelination syndrome (Guillain Barre) characterised by ascending paralysis
37
Q

What is the incubation period of campylobacter?

A

2-5 days

38
Q

What are the symptoms of campylobater infection?

A
  • Bloody diarrhoea
  • Cramping abdominal pain
  • Vomiting is not usually a feature
  • Fever
39
Q

What is the normal duration of campylobacter?

A

2-10 days

40
Q

What is the treatment of campylobacter?

A
  • Fluid replacement is sufficient in most cases
  • Clarithromycin/erythromycin for severe/persistent disease
  • Quinolone (e.g. ciprofloxacin) or amino glycoside (e.g. gentamicin) for invasive disease
41
Q

What are the specific control points for campylobacter infection?

A
  • Reduction of contamination in raw, retail poultry meat

* Adequate cooking

42
Q

What is the appearance of Escherichia coli?

A

Gram negative bacilli

43
Q

What are the different groups of Escherichia coli?

A
  • Enteropathogenic
  • Enterotoxigenic
  • Enterohaemorrhagic
  • Enteroinvasive
  • Entero-aggregative
  • Diffuse aggregative
44
Q

What is the pathogenesis of Enteropathogenic E coli (EPEC)

A
  • Initial adherence via pili
  • Attaching and effacing lesion mediated by intimin protein and Tir (translocated intimin receptor) with disruption of intestinal microvilli
45
Q

What is the incubation period of EPEC?

A

1-2 days

46
Q

What is the duration of EPEC infection?

A

1-several weeks

47
Q

What are the symptoms of EPEC?

A
  • Watery diarrhoea
  • Abdominal pain
  • Vomiting
  • Often accompanied by fever
48
Q

What is the major cause of travellers diarrhoea?

A

ETEC

49
Q

What is the pathogenesis of ETEC?

A

Diarrhoea due to the action of 1 or 2 plasmid encoded toxins:

  • heat labile
  • heat stable
50
Q

What is the incubation period of ETEC?

A

1-7 days

51
Q

What is the duration of ETEC infection?

A

2-6 days

52
Q

What are the symptoms of ETEC?

A
  • Watery diarrhoea
  • Abdominal pain
  • Vomiting
  • No associated fever
53
Q

Which type of E coli is known as E coli 0157?

A

Enterohaemorrhagic E coli (EHEC)

54
Q

What is the transmission of EHEC?

A
  • Large animal reservoir in cattle and sheep
  • Consumption of contaminated food, water and dairy products and direct environmental contact with animals
  • secondary person to person spread is important
55
Q

What is the pathogenesis of EHEC?

A
  • Attaching and effacing lesion
  • Production of Shiga like toxins
  • Structural and functional analogue of shigella dusenteriae toxin or VTEC
56
Q

What is the incubation period of EHEC?

A

1-7 days

57
Q

What is the duration of EHEC infection?

A

5-10 days

58
Q

What are the symptoms of EHEC infection?

A
  • bloody diarrhoea
  • Abdominal pain
  • Vomiting
  • no associated fever
59
Q

What are the clinical signs of haemolytic uraemic syndrome and what causes it?

A
  • Microangiopathic haemolytic anaemia
  • Thrombocytopenia
  • Acute renal failure
  • EHEC

Week 7 - microbiology (12 decks)

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