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Semester 2 > Microbiological Diagnosis of Chest Infection COPY > Flashcards

Microbiological Diagnosis of Chest Infection COPY Flashcards

1
Q

What diagnostic techniques are used for chest infections?

A
  • Microscopy and culture of blood and sputum
  • Antigen detection methods
  • Nucleic acid amplification (PCR)
  • Serology (antibody measurement)
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2
Q

How valuable is gram staining for organisms and pus cells?

A

Limited value

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3
Q

What are the 3 major respiratory pathogens?

A
  • Strep pneumoniae
  • Hameophilius influenzae
  • Moraxella Catarrhalis
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4
Q

What may you expect to find in sputum cultures?

A

Normal upper respiratory flora such as viridans streps

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5
Q

What does previous antibiotic therapy select out?

A

Organisms that are not respiratory pathogens such as:

  • E. coli
  • Staph aureus
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6
Q

How must sputum cultures be interpreted?

A

Using the clinical presentation:

  • Community pneumonia
  • Aspiration pneumonia
  • Ventilated patient pneumonia
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7
Q

How is TB diagnosed?

A

Using ZN or auramine phenol stain

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8
Q

How is TB described?

A

Acid and Alcohol Fast Bacilli (AAFB)

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9
Q

How is a broncho-alveolar lavage done?

A
  • Lower airway sample collected at bronchoscopy

- Catheter aspirate in ventilated patient

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10
Q

What is BAL used in the diagnosis of?

A

Ventilator associated pneumonia

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11
Q

What is an advantaged of BAL?

A

Less liable to contamination- more accurate diagnosis of LRTI

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12
Q

What does BAL produce?

A

Quantitative culture of BAL- colony forming units/ml (cfu/ml)

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13
Q

Who are blood cultures taken from?

A

Any patient with severe sepsis

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14
Q

What do many patients with pneumonia have in their blood?

A

Bacteraemia (viable bacteria in the blood)

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15
Q

Why is blood culture carried out?

A

There are too few organisms in blood to see on microscopy

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16
Q

How is blood culture carried out?

A

Blood inoculated into 2 bottle containing culture media and incubated

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17
Q

What happens on day 1 of blood culture?

A
  • Microscopy positive in 6-48 hours (Gram stain)
  • Result is phoed to the clinician and interim recommendations on antibiotics
  • Overnight subculture of sensitivity and identification tests
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18
Q

What happens on day 2 of blood culture?

A

-Full ID and sens- clinical significance is re-assessed

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19
Q

What organisms are not easily cultured and are known as atypical causes?

A
  • Legionella pneumophila
  • Mycoplasma pneumoniae
  • Chlamydia psittaci
  • Coxiella burnetti
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20
Q

What is antigen detection?

A
  • Non-cultural methods of demonstrating the presence of an organism
  • Detect specific antigen immunologically
21
Q

What antigens can be detected in urine?

A

Legionella and pneumococcal

22
Q

What antigens can be detected in naso-pharyngeal secretions?

A

Viruses

23
Q

What techniques are used in antigen detection?

A
  • Agglutination
  • EIA
  • Immunofluorescence
24
Q

How is latex agglutination done?

A
  • Latex particles coated with monoclonal antibodies that are specific for the organism in question are mixed with the clinical specimen
  • Agglutination (clumping) visible by naked eye
25
Q

What does EIA stand for?

A

Enzyme Immuno-Assay

26
Q

What does ELISA stand for?

A

Enzyme Linked Immunosorbent Assay

27
Q

How is a positive EIA/ELISA result generated?

A

Linked enzyme on 2nd antibody generates colour change

28
Q

What is monoclonal antibody the product of?

A

A single clone of plasma cells

29
Q

Give an example of how ELISA/EIA works.

A
  • Monoclonal anti-Legionella coated on well of microtitre plate
  • Incubated with patients’s urine- antigen binds if present
  • Incubated with enzyme linked monoclonal anti-Legionella
  • Enzyme substrate added- colour change if enzyme present
30
Q

What technique is used for DNA detection?

A

Polymerase chain reaction (PCR)

31
Q

What specific primers are used in PCR?

A

Short oglionucleotide sequences

32
Q

How does PCR work?

A
  • Short oglionucleotide sequences bind to target DNA sequences
  • Multiple copies of target sequence are produced
  • Amplified copies of DNA easily detected
33
Q

What is an advantage of PCR?

A

Very sensitive

34
Q

What is a disadvantage of PCR?

A

False positives due to contamination

35
Q

What does real time PCR allow?

A

Enables product of the reaction to be measured as the reaction progresses

36
Q

What is the generic term for the technical variations of PCR?

A

Nucleic acid amplification test (NAAT)

37
Q

What samples must be collected for diagnosis by PCR?

A

Throat swabs or other respiratory sample

38
Q

What kind of swab is used for PCR?

A

Flocked swab

39
Q

What is routinely screened for using PCR?

A

Mycoplasma pneumoniae

and a wide range od respiratory viruses (multiples assays)

40
Q

What respiratory viruses are screened for using multiplex assays?

A
  • Influenza A and B
  • Adenovirus
  • RSV
  • Parainfluenza
  • Metapneumovirus
  • Coronavirus
  • Rhinovirus
41
Q

What does antibody detected by serology measure?

A

Host antibody response to organism

42
Q

What is it usually difficult to do with antibody detection by serology?

A

Culture or detect the organism directly

43
Q

What was antibody detection by serology previously used for?

A

Viral infections and so called atypical causes of pneumonia

44
Q

What is IgM a marker of?

A

Current infection

45
Q

What is IgG a marker of?

A

Previous infection

46
Q

What must be demonstrated if total antibody is measured?

A
  • A significant increase in levels during the coarse of the illness
  • Takes some time for antibody levels to rise
47
Q

What is antibody measurement now mostly used to determine?

A

Vaccine response

48
Q

What organisms cause difficult to diagnose bacterial infections?

A
  • Legionella penumophilia
  • Chamydia psittaci
  • C penumoniae
  • Coxiella burnetti

Semester 2 (150 decks)

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