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Microbiology 2 > Week 3 - GIT disorders continued > Flashcards

Week 3 - GIT disorders continued Flashcards

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1
Q

What is some of the epidemiology of Salmonella gastroenteritis?

A
  • Source usually animals
  • Vehicle usually food (temp abuse)
  • Humans excrete for a week or two after infection but are rarely long-term carriers.
  • Occasionally acquired from another person.
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2
Q

What is the infective dose required for Salmonella gastroenteritis?

A

Greater than 10^5 organisms (high infective dose)

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3
Q

If Salmonella spp. gets killed by stomach acid, how do numbers high enough to cause disease pass through?

A

Pass through in food masses.

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4
Q

Which areas of the GIT do Salmonella spp. attach to and then enter cells?

A

Small intestine and colon.

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5
Q

What are the clinical symptoms of Salmonella gastroenteritis?

A

Nausea and vomiting followed by diarrhoea and fever. Complete recovery

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6
Q

What is the incubation period of Salmonella gastroenteritis?

A

1-2 days

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7
Q

What is the duration period of Salmonella gastroenteritis?

A

3-7 days

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8
Q

What is the treatment for Salmonella gastroenteritis?

A

Fluids and electrolytes.

Antibiotics if septicaemia is present.

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9
Q

What are Virulence plasmids in Salmonella?

A

Many serovars of Salmonella possess plasmids which are essential for salmonellae to produce systemic disease.
Virulence plasmids range in size from 50 to 90kb.
They have a highly conserved region of approximately 8kb encompassing five genes which are related to virulence.
The genes are now designated spvRABCD (salmonella plasmid virulence)

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10
Q

What are some discoveries about antibiotic resistance in Salmonella?

A
  • Salmonella genomic isalnd 1 (SGI1) is the first genomic island reported to contain an antibiotic resistance gene cluster
  • It was identified in the multidrug-resistant Salmonella enterica serovar Typhimurium DT104.
    The antibiotic resistance genes are clustered in a 13-kb segment within a 43-kb genomic island.
    All resistance genes are contained within a complex integron structure.
  • One study found that 60% of meat is contaminated with Salmonella. Half of isolated had resistance to more than one class of drug. One isolated was multi-drug resistant.
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11
Q

What are some of the general characteristics of Campylobacter?

A
  • Small, curved motile
  • Gram negative rods
  • Microaerophillic (5% O2) - fastidious
  • Most pathogenic speicies are thermophillic as they are naturally found in the GIT of pultry @ 43 degrees.
  • Exhibit darting motility - move in corkscrew fashion which helps to get through the intestinal mucous.
  • Coccoid forms develop in older cultures which are viable but not about to be cultured.
  • Has a small genome.
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12
Q

What are some of the most common types of Campylobacter?

A

C. jejuni, C. coli, C. fetus. C. lari, C, upsaliensis.

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13
Q

What are some of the symptoms of Campylobacter?

A

May be subclinical or may cause disease of varying severity.

C. jejuni infection typicall yresults in abdominal pain, fever and diarrhoea which may be mucopurulent or bloddy

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14
Q

What are some unusual disease manifestations of Campylobacter?

A

Campylobacter has been associated with rare sequelae including reactive arthritis and Guillain-Barre syndrome.
Human infection with C. fetus may cause localised abscesses or generalised sepsis particularly in immunosuppressed persons.

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15
Q

How does transmission of Campylobacter occur?

A
  • Commensal of birds are of the most common causes of gastroenteritis
  • Up to 85% of chickens infected
  • ~95% of chicken products are contaminated
  • Sources of infection included unpasteurised milk, water, pets, young adults and children.
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16
Q

What is the basic pathogenesis of Campylobacter?

A
  • After ingestion is passes through the stomach protected by food masses
  • C. jejuni is killed by acid in stomach
  • Infective dose 100 bacteria
  • Main site of colonisation is the jejunum but the colon may also be involved.
  • Penetrates mucosa and invades lamina propria where it damages the epithelium and causes symptoms.
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17
Q

How do Campylobacter bacteria get into the host cell?

A
  • Attaches to the epithelial lining using its’ flagella.
  • Once attached to surface of cell it produces a protein called CadF. This binding triggers rearrangement of the host cytoskeleton.
  • At this point they also secrete HTRA enzyme which breaks down tight junctions. This might allow the bacteria to move between the tight junctions and then infect cells from underneath like Shigella.
  • Signalling pathways in the host cell are activated which cause actin to rearrange and take up the C.jejuni into a vacuole.
  • Inside the cell, the production of toxin blocks the transition to the G2 phase ultimately causing cell death.
  • Damage to the epithelial lining caused the sub-mucosa to be exposed leading to blood in the stool.
18
Q

What are some of the immunological complications of Campylobacter?

A 
Guillain Barre Syndrome (C. jejuni most common)
Generalised paralysis (acute/chronic)
Reactive Arthritis (C. jejuni, C. coli, C. concisus)
19
Q

How does Campylobacter infection cause generalised paralysis?

A

Because of antigenic mimicry between LPS and human gangliosides that are found on the surface of neurons, patients can develop antibodies which attack neurons causing neurological symptoms. this can lead to generalized acute or chronic paralysis and pain.

20
Q

What is the treatment for Campylobacter infection?

A

Management of symptoms
Fluid replacement only in mild cases
Severe cases may require treatment with erythromycin or clarithromycin.

21
Q

What biochemical tests might be performed to identify Campylobacter?

A 
Catalase
H2S prudction i n triple sugar agar
Growth at 25C, 42C to distinguish species
Sensitivity to nalidixic acid and cephalothin
Hippurate hydrolysis
Nitrate reduction
Growth in 1% glycerine
Indoxyl acetate hydrolysis
22
Q

What are some antibiotics that Campylobacter has shown resistance to?

A 
Tetracyline
Erythromycin
Ciprofloxacin
Kanamycin
Nalidixic acid
Chloramphenicol
23
Q

What are the four significant groups of virus types which cause viral gastroenteritis?

A

Rotaviruses
Caliciviruses i.e. Norovirus, Sapporo virus
Astroviruses
Enteric adenoviruses

24
Q

How common is viral gastroenteritis and who is most affected?

A

Extremely common. 95% of children are infected with Rotavirus by 5 years.
Children in developing countries = major cause of death
Adults = norovirus, usually a common source i.e. seafood

25
Q

What are the clinical signs and symptoms of viral gastroenteritis in children and what is the outcome?

A

Incubation 24-48 h
Diarrhoea, vomiting, +/- fever
Dehydration a concern in young children
Lasts for up to one week, resolves completely

26
Q

What are the clinical signs and symptoms of viral gastroenteritis in adults and what is the outcome?

A

Incubation period 24-48 h
Diarrhoea, nausea, vomiting, +/- fever
Complete resolution 12-60 hours

27
Q

What is the physiological mechanism that causes vomiting in viral gastroenteritis?

A

Inflammation in the GIT triggers the vagus nerve and causes vomiting.

28
Q

What is the Family, DNA/RNA structure, size and shape of Rotavirus?

A 
Family = Reoviridae
Structure = ds RNA
Size = 65nm
Shape = icosahedral
29
Q

What is the Family, DNA/RNA structure, size and shape of Adenovirus types 40 and 41?

A 
Family = Adenoviridae
Structure = ds DNA
Size = 80nm
Shape = icosahedral
30
Q

What is the Family, DNA/RNA structure, size and shape of Norovirus?

A 
Family = Caliciviridae
Structure = ss RNA
Size = 27nm
Shape = icosahedral
31
Q

What is the Family, DNA/RNA structure, size and shape of Astrovirus?

A 
Family = Astroviridae
Structure = ss RNA
Size = 28nm
Shape = icosahedral
32
Q

What is the epidemiology of Rotavirus?

A

Most common cause of gastroenteritis in under 5’s.
Occasionally occurs in adults (most have IgA)
Most common in autumn and winter
Virus shedding - 2.5 days after onset
Asymptomatic infections can still shed virus
Diarrhoeal stools have 10^10 - 10^11 viruses/g
Infection dose low = 10 virions
Stable in environment, resists drying, can live in toys
Can be spread from person to person

33
Q

What is the epidemiology of Adenovirus types 40 and 41?

A

Second to Rotavrius as a cause of gastroenteritis in children.

34
Q

What is the epidemiology of Norovirus?

A

Causes gastroenteritis in adults.

35
Q

What is the epidemiology of Astrovirus?

A

Gastroenteritis in babies and young children.

36
Q

What is the treatment/management for viral gastroenteritis?

A

No antiviral drugs avaialable
Maintain fluids
Intravenous fluids may be necessary

37
Q

What are some of the characteristics of Rotavirus?

A

It has icosahedral symmetry
Resembles a wheel
Double stranded RNA
Double layered capsid
Segmented genome (re-assortment can occur, creation of new viruses)
Two serotypes affect humans, other serotypes affect different animal species and can occasionally affect humans.

38
Q

What is the clinical presentation of Rotavirus?

A 
Incubation 1-2 days
Acute onset
Projectile vomiting, diarrhoea, fever
Dehydration
Often can show respiratory symptoms for unknown reasons
Lasts up to one week
Complete recovery
39
Q

What is the basic pathogenesis of Rotavirus?

A

Survives stomach acid

Infects the columnar epithelial cells at the tips of villi i nthe small intestine.

40
Q

What are the virulence factors of Rotavirus?

A

VP4 spike protein - Adhesin

NSP4 toxin

Microbiology 2 (4 decks)

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