Microbiology Diagnosis of Chest Infections

Question 1

name some diagnostic techniques

Answer 1

> microscopy and culture of sputum
antigen detection methods
nucleic acid amplification
serology

Question 2

what are the major respiratory pathogens that are cultured for?

Answer 2

> strep. pneumonia
haemophilus influenza
Moraxella catarrhalis

Question 3

what ways can a bronchio-alveolar lavage sample be taken?

Answer 3

> a lower airways sample collected via bronchoscopy

> a catheter aspirate in ventilated patient (more representative of the patients lung)

Question 4

what sort of culture is created from a BAL?

Answer 4

a quantative culture in units/ml to show the colony count

Question 5

what sort of pneumonia is BAL used to diagnose?

Answer 5

ventilator associated pneumonia

Question 6

when are blood cultures taken from a patient?

Answer 6

when they have severe sepsis, presenting with an increased heart and respiratory rate

Question 7

after a blood culture why is a gramm stain carried out?

Answer 7

to rationalise what antibiotic the patient should be on

Question 8

what organisms can not easily be blood cultured?

Answer 8

> legionella pneumophila
mycoplasma pneumonia
chlamydia psittaci
coxiella burnetti

Question 9

what is antigen detection?

Answer 9

this is a non-cultural demonstration of the presence of an organism by detecting the specific antigen in immunology.

Question 10

in latex agglutination what are the latex particle coated with?

Answer 10

monoclonal antibodies specific for organism in question.

Question 11

in latex angulation how can you tell if the organism is present?

Answer 11

there is clumping that is visible to the naked eye

Question 12

what does EIA stand for?

Answer 12

enzyme linked immuno-assay

Question 13

describe the process of EIA/ELISA

Answer 13

the monoclonal anti-legionella is coated on a well of micro titre plate. this is then incubated with the patients urine and if the antigen is present it will bind. this is incubated with enzyme linked monoclonal anti-legionella and then anything that is not attached is washed away. the enzyme substrate is added and a colour change will occur if the enzyme is present. the more antigen present the denser the colour will occur.

Question 14

why may a false positive occur in a polymerase chain reaction?

Answer 14

if there is contamination as it is very sinsitive

Question 15

describe how the DNA molecule in PCR is amplified for visualisation

Answer 15

it is denatured at 95 degrees. at 60 degrees the primers anneal to complementary bases flanking the region of interest. at 75 degrees tag polymerase extends the single stranded DNA molecule creating a double stranded DNA molecule. this process is repeated 25-35 times.

Question 16

name the respiratory viruses

Answer 16

> influenza A and B
> Adenovirus
> RSV
> Parainfluenza virus
> metapneumovirus
> coronavirus
> rhinovirus

Question 17

what does serology measure?

Answer 17

the hosts antibody response to an organism when it is difficult to culture or detect the organism directly

Question 18

what does IgM indicate?

Answer 18

that there is a current infection

Question 19

what does IgG indicate?

Answer 19

a previous infection

Question 20

what do you have to demonstrate if you are looking at the total antibody count in serology?

Answer 20

that there is a significant increase in levels during the course of the illness, a rising titre

Question 21

what is a AAFB bacteria?

Answer 21

a bacteria that is de-colourised by an acid or an alcohol such as tuberculosis