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Phase 2a diseases > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is the process of gram staining a bacterial sample?

A

1) Crystal violet
2) Wash off
3) Iodine
4) Wash off
5) Decolourise the bacteria
6) Add a counter stain

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2
Q

What colour do gram +ve and gram -ve bacteria go?

A
  • PurPle = Positive

- piNk = Negative

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3
Q

What are some examples of gram +ve bacteria?

A
  • Staphylococci

- Streptococci

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4
Q

What are some examples of gram -ve bacteria?

A
  • Coliforms

- Neisseria

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5
Q

What are round bacteria called?

A

Cocci

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6
Q

What are rod-shaped bacteria called?

A

Bacilli

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7
Q

How can gram +ve cocci be further classified?

A
  • Clustered
  • Chained
  • Paired
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8
Q

What are chains of gram +ve cocci called?

A
  • Streptococci
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9
Q

What are chains of gram -ve cocci called?

A
  • Staphylococci
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10
Q

How can all of the streptococci be further classified?

A

Haemolysis on blood agar:

  • Beta haemolysis (complete clearance) suggests B-haemolytic strep.
  • Alpha haemolysis (green) suggests alpha-haemolytic strep.

For all the alpha haemolytic strep, an optochin test should be performed:

  • Sensitivity to optochin suggests streptococcus pneumoniae.
  • Resistance suggests Viridans streptococci.
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11
Q

How are the staphylococci further classified?

A

Coagulase DNAse test:

  • +ve indicates staphylococcus aureus.
  • -ve indicates another form of coagulase -ve staphylococcus (commonly staphylococcus epidermidis).
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12
Q

What is the pathway to reach a conclusion a sample contains staphylococcus aureus?

A

Gram stain: Gram +ve.
Shape: Round (cocci) and in clusters (staphylo)

Therefore, the sample is a staphylococcus.

Conduct a coagulase DNA test:
- +ve result means it is staphylococcus aureus.

SIDE NOTE: staphylococcus aureus will appear creamy/yellow when cultured on blood agar.

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13
Q

What is the pathway to reach a conclusion a sample contains streptococcus pneumoniae?

A

Gram stain: Gram +ve
Shape: Round (cocci) and in chains (strepto)

Therefore, the sample is streptococci.

Conduct a blood agar haemolysis test: Alpha haemolysis (green).

Conduct optochin test: If sample is sensitive to optochin, it is probably strep pneumoniae.

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14
Q

What important diseases can be caused by streptococcus pneumoniae?

A
  • Lobar pneumonia

- Meningitis

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15
Q

Why are samples of gram -ve bacteria more likely to be contaminated than gram +ve ones?

A
  • Gram -ve bacteria more commonly come from non-sterile sites (e.g. mouth, skin, vagina, urethra, large intestine).
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16
Q

How are gram -ve bacilli further classified?

A

Gram -ve bacilli = Pink, rod shaped organisms.

1) MacConkey agar:
- If pink, they are lactose fermenting.
- If yellow/colourless, they are not lactose fermenting.

2) If the bacteria are not lactose fermenting, conduct an oxidase test:
- +ve oxidase example is pseudomonas aeruginosa.
- -ve oxidase example is shigella.

3) If further differentiation is needed, more detailed biological tests will need conducting.

17
Q

What is the pathway to reach a conclusion a sample contains pseudomonas aeruginosa?

A

1) Gram -ve bacilli (pink, rod shaped).
2) MacConkey agar: non-lactose fermenting (clear/yellow).
3) Oxidase test: +ve result indicates it could be pseudomonas aeruginosa.

18
Q

What are the two main approaches to viral diagnosis?

A
  • Virus detection

- Serology

19
Q

What is the main method of virus detection now used?

What are the advantages and disadvantages?

A

PCR

+ Highly sensitive.
+ Quick.

  • Only works after viral probe has been developed.
  • Sensitive to laboratory contamination.
20
Q

What does serology investigate with regard to viral diagnosis?

A
  • IgM antibodies and IgG antibodies.
  • IgM appears within one week of viral infection, and remains positive up to 12 weeks beyond.
  • IgG appears later but will remain positive for many years (sometimes a lifetime!). It is IgG that is responsible for providing immunity upon reinfection.
  • Therefore, either IgG or IgM virus specific antibodies can be used to diagnose viral infections.
21
Q

What virus typically causes glandular fever?

A

Epstein Barr Virus (EBV)

22
Q

What will serology tests typically show for glandular fever?

A
  • Atypical lymphocytes on blood film.

- Significant IgM antibody titre.

23
Q

Why is a bacterial swap important if glandular fever is suspected?

A
  • Sometimes there is a bacterial differential diagnosis, so charcoal bacterial swab should be taken to rule these out.
24
Q

What are the symptoms associated with glandular fever?

A
  • Fatigue
  • Malaise
  • Loss of appetite
  • Cough
  • Sore throat
  • Tonsils red with white patches, and swollen.
25
Q

What is the treatment for glandular fever?

A
  • Supportive therapy.

- Avoid contact sports for 6 weeks (risks spleen rupture).

26
Q

What virus causes shingles?

A
  • Varicella Zoster Virus (VZV)

- Usually from a reactivation of VZV after chickenpox.

27
Q

What is the typical presentation of shingles

A
  • Rash with dermatomal distribution, usually seen in areas associated with tight clothing (ties, belts etc.)
28
Q

How does CMV colitis typically present?

A
  • ‘Owl’s eye’ inclusion bodies in the enterocytes.
29
Q

What are the three markers that can be tested for to diagnose HIV?

A
  • HIV antibodies
  • HIV antigens
  • HIV RNA
30
Q

What is the sensitivity/specificity of HIV testing like in the UK?

What does this mean when diagnosing a patient with HIV?

A
  • High sensitivity/low specificity.

- Means if a positive result is reported, a confirmatory re-test will need to be done.

31
Q

How does CSF differ in patients with viral meningitis compared to those with bacterial meningitis?

A

Viral meningitis:

  • Lymphocytic
  • Normal protein and glucose
  • Clear CSF

Bacterial meningitis:

  • Much higher WBC count
  • Raised protein
  • Low glucose
  • Turbid (cloudy/thick) CSF

Phase 2a diseases (18 decks)

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