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A2. Respiratory system > Microbiological diagnosis of Chest Infection > Flashcards

Microbiological diagnosis of Chest Infection Flashcards

1
Q

What are the diagnostic techniques for chest infection?

A

Microscopy and culture of sputum and blood

Antigen detection methods

Nucleic acid amplification

Serology (measures antibodies)

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2
Q

What are the key aspects of microscopy and culture of sputum?

A

Gram stain

Culture for major respiratory pathogens

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3
Q

What are the significant major respiratory pathogens?

A

Strep pneumoniae
Haemophilus influenzae
Moraxella Catarhallis

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4
Q

How do you make sense of the sputum culture results?

A

Normal upper respiratory are not usually significant

Previous antibiotic therapy can be used to destroy E.Coli and Staph Aureus ruling them out from the cause of respiratory infection

Patient history can be used to distinguish between Community pneumonia vs aspiration pneumonia and ventilated patient

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5
Q

What stain is used for TB?

A

ZN or Auramine

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6
Q

TB is classed as an AAFB what does this mean?

A

Alcohol and acid fast bacilli - it cannot be decolourised by acids and alcohols

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7
Q

What length of time is required for TB culture?

A

Extended

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8
Q

When will M tuberculosis be able to be identified?

A

Only once it has grown

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9
Q

What is bronchiolar lavage?

A

A medical procedure in which a bronchoscope is passed through the mouth or nose into the lungs and fluid is squirted into a small part of the lung and then collected for examination.

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10
Q

In which part of the lung is airway sample collected?

A

Lower portions of the airway

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11
Q

What are the main advantages of a Bronchio-alveolar lavage?

A

Allows a quantitive culture in colony forming units per millilitre. (cfu/ml)

Less liable to contamination

Used for diagnosis of ventilator associated pneumonia

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12
Q

Who are blood cultures likely to be taken from?

A

Those with severe sepsis or bacteraemia.

Bacteraemia common in pneumonia patients

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13
Q

Is microscopy possible for blood samples?

A

No

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14
Q

When blood tubes are intubated how do they know if bacteria are present?

A

Build up of CO2 which will be picked up by a scanner - process usually takes less than 48 hours

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15
Q

What is done after bacteria in the blood is confirmed?

A

Overnight sub culture to assess identification and sensitivity

Day 2 confirms the bacteria and its sensitivity

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16
Q

Which organisms are not easily cultured (atypical causes)?

A

Legionella pneumophila
Mycoplasma pneumoniae
Chlamydia psittaci
Coxiella burnetti

17
Q

What is a non-cultural method of demonstrating presence of an organism?

A

Detect specific antigen immunologically

PCR

18
Q

Which antigens can be detected in urine and naso-pharyngeal secretions?

A

Legionella and pneumococcal antigen

19
Q

What is latex agglutination?

A

Monoclonal antibodies are added to latex particles

This is then mixed with the clinical specimen

Agglutination is then possible with the naked eye if the organism is present.

20
Q

What is a EIA?

A

Enzyme immunoassay

21
Q

What does ELISA stand for?

A

Enzyme linked immunosorbent assay

22
Q

How does an EIA work?

A

Specific antibody detects antigen

Linked enzyme on 2nd antibody generates colour change when the substrate is added

23
Q

How does PCR detect DNA?

A

Specific short primers are added

Multiple copies of the target sequence are produced and detected

24
Q

How can false positive results come about when using DNA detection?

A

Contamination

25
Q

What is real time PCR?

A

Quantitive PCR - allows the product of the reaction to be measured as the reaction progresses

26
Q

How is respiratory diagnosis achieved by PCR?

A

Throat swabs or other respiratory samples are used

27
Q

What are the common respiratory viruses?

A 
Influenza A and B
Adenovirus
RSV
Parainfluenza viruses
Metapneumovirus
Coronavirus
Rhinovirus
28
Q

What is meant by serological diagnosis?

A

Antibody detection - It is a measure of the hosts antibody response to an organism, usually used when the culture or detection of the organism is difficult.

Previously used for viral infections infections and atypical causes of pneumonia

29
Q

What does IgM represent in serology?

A

Current infection

30
Q

What does IgG represent in serology?

A

Previous infection

31
Q

How should the level of antibody change during the course of an infection?

A

Increase, although it takes some time for the antibody levels to rise (rising titre)

32
Q

What other practical use does antibody measurement have?

A

Can be used to determine immunity (vaccine response)

33
Q

What bacteria are difficult to diagnose?

A 
Legionella pneumophila (urinary antigen and sputum culture)
Chlamydia psittaci and C. pneumoniae
Coxiella burnetii (Q fever

A2. Respiratory system (77 decks)

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