Microbiological Diagnosis of Chest Infection

Question 1

What diagnostic techniques are used for chest infections?

Answer 1

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

Question 2

How valuable is gram staining for organisms and pus cells?

Answer 2

Limited value

Question 3

What are the 3 major respiratory pathogens?

Answer 3

• Strep pneumoniae
• Hameophilius influenzae
• Moraxella Catarrhalis

Question 4

What may you expect to find in sputum cultures?

Answer 4

Normal upper respiratory flora such as viridans streps

Question 5

What does previous antibiotic therapy select out?

Answer 5

Organisms that are not respiratory pathogens such as:

• E. coli
• Staph aureus

Question 6

How must sputum cultures be interpreted?

Answer 6

Using the clinical presentation:

• Community pneumonia
• Aspiration pneumonia
• Ventilated patient pneumonia

Question 7

How is TB diagnosed?

Answer 7

Using ZN or auramine phenol stain

Question 8

How is TB described?

Answer 8

Acid and Alcohol Fast Bacilli (AAFB)

Question 9

How is a broncho-alveolar lavage done?

Answer 9

• Lower airway sample collected at bronchoscopy

- Catheter aspirate in ventilated patient

Question 10

What is BAL used in the diagnosis of?

Answer 10

Ventilator associated pneumonia

Question 11

What is an advantaged of BAL?

Answer 11

Less liable to contamination- more accurate diagnosis of LRTI

Question 12

What does BAL produce?

Answer 12

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

Question 13

Who are blood cultures taken from?

Answer 13

Any patient with severe sepsis

Question 14

What do many patients with pneumonia have in their blood?

Answer 14

Bacteraemia (viable bacteria in the blood)

Question 15

Why is blood culture carried out?

Answer 15

There are too few organisms in blood to see on microscopy

Question 16

How is blood culture carried out?

Answer 16

Blood inoculated into 2 bottle containing culture media and incubated

Question 17

What happens on day 1 of blood culture?

Answer 17

• 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

Question 18

What happens on day 2 of blood culture?

Answer 18

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

Question 19

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

Answer 19

• Legionella pneumophila
• Mycoplasma pneumoniae
• Chlamydia psittaci
• Coxiella burnetti

Question 20

What is antigen detection?

Answer 20

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

Question 21

What antigens can be detected in urine?

Answer 21

Legionella and pneumococcal

Question 22

What antigens can be detected in naso-pharyngeal secretions?

Answer 22

Viruses

Question 23

What techniques are used in antigen detection?

Answer 23

• Agglutination
• EIA
• Immunofluorescence

Question 24

How is latex agglutination done?

Answer 24

• 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

Question 25

What does EIA stand for?

Answer 25

Enzyme Immuno-Assay

Question 26

What does ELISA stand for?

Answer 26

Enzyme Linked Immunosorbent Assay

Question 27

How is a positive EIA/ELISA result generated?

Answer 27

Linked enzyme on 2nd antibody generates colour change

Question 28

What is monoclonal antibody the product of?

Answer 28

A single clone of plasma cells

Question 29

Give an example of how ELISA/EIA works.

Answer 29

- 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

Question 30

What technique is used for DNA detection?

Answer 30

Polymerase chain reaction (PCR)

Question 31

What specific primers are used in PCR?

Answer 31

Short oglionucleotide sequences

Question 32

How does PCR work?

Answer 32

- Short oglionucleotide sequences bind to target DNA sequences - Multiple copies of target sequence are produced - Amplified copies of DNA easily detected

Question 33

What is an advantage of PCR?

Answer 33

Very sensitive

Question 34

What is a disadvantage of PCR?

Answer 34

False positives due to contamination

Question 35

What does real time PCR allow?

Answer 35

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

Question 36

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

Answer 36

Nucleic acid amplification test (NAAT)

Question 37

What samples must be collected for diagnosis by PCR?

Answer 37

Throat swabs or other respiratory sample

Question 38

What kind of swab is used for PCR?

Answer 38

Flocked swab

Question 39

What is routinely screened for using PCR?

Answer 39

Mycoplasma pneumoniae | and a wide range od respiratory viruses (multiples assays)

Question 40

What respiratory viruses are screened for using multiplex assays?

Answer 40

- Influenza A and B - Adenovirus - RSV - Parainfluenza - Metapneumovirus - Coronavirus - Rhinovirus

Question 41

What does antibody detected by serology measure?

Answer 41

Host antibody response to organism

Question 42

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

Answer 42

Culture or detect the organism directly

Question 43

What was antibody detection by serology previously used for?

Answer 43

Viral infections and so called atypical causes of pneumonia

Question 44

What is IgM a marker of?

Answer 44

Current infection

Question 45

What is IgG a marker of?

Answer 45

Previous infection

Question 46

What must be demonstrated if total antibody is measured?

Answer 46

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

Question 47

What is antibody measurement now mostly used to determine?

Answer 47

Vaccine response

Question 48

What organisms cause difficult to diagnose bacterial infections?

Answer 48

- Legionella penumophilia - Chamydia psittaci - C penumoniae - Coxiella burnetti