Microbiological Diagnosis of Chest Infection

Question 1

What are the four main methods used by microbiologists to diagnose chest infections

Answer 1

• microscopy and culture of sputum/blood
• antigen detection
• nucleic acid amplification (PCR)
• serology/antibody measurement

Question 2

Name the main respiratory pathogens that can be identified by overnight culturing

Answer 2

• strep pneumoniae
• haemophilus influenzae
• moraxella catarrhalis

Question 3

What staining techniques are used to identify TB infection

Answer 3

ZN/Auramine staining

Question 4

What type of pathogen in mycobacterium tuberculosis

Answer 4

acid and alcohol fast bacilli (AAFB - resist discolouration by acid and alcohol)

Question 5

What is a bronchoalveolar lavage and what does it indicate

Answer 5

• lower airway sample collected by bronchoscopy
• liquid squirted and sucked back up
• amount of organism detectable

Question 6

What are the advantages of BAL

Answer 6

• less liable to contamination (more accurate diagnosis)

- used for diagnosis of ventilator associated pneumonia

Question 7

How can bacteraemia be diagnosed/detected

Answer 7

• blood must be cultured as there are too few organisms to be seen my microscopy
• day one allows interim antibiotic recommendation
• day two allows exact ID and sensitivity testing

Question 8

Name the four atypical causes of pneumonia, those that are not easily cultured

Answer 8

• legionella pneumophilia
• mycoplasma pneumoniae
• chlamidia psittaci/pneumoniae
• coxiella burnetti

Question 9

Describe the principle of latex agglutination

Answer 9

• latex particles covered with antibodies for a particular condition
• mixed with specimen (urine/nasopharangeal secretions)
• clumping visible with naked eye

Question 10

What is EIA/ELISA

Answer 10

• enzyme immuno-assay

- enzyme linked immunosorbent assay

Question 11

Describe the principle of EIA/ELISA

Answer 11

• antibody for condition placed on plate
• specimen added and antigen binds if present
• enzyme-linked antibodies added that bind to antigen if present
• the enzyme’s substrate is added and a colour change is observed if the antigen is present
• washing between stages is essential

Question 12

Name a disadvantage to PCR

Answer 12

false positives often recorded due to contamination

Question 13

Name some of the main respiratory viruses

Answer 13

• influenza A/B
• adenovirus
• rhinovirus
• parainfluenza virus 1/2/3/4

Question 14

What is IgM a marker of in serology

Answer 14

current infection

Question 15

What is IgG a marker of in serology

Answer 15

previous infection