Microbiological Diagnosis of Chest Infection Flashcards
What is 4 examples of diagnostic techniques
Microscopy and culture of sputum and blood
Antigen detection methods
Nucleic acid amplification (PCR)
Serology (antibody measurement)
What do you gram stain sputum for
organelles and pus cells
What is of better value than gram staining in microscopic diagnostic of chest infection
culturing for major respiratory pathogens overnight
What are the major respiratory pathogens
Strep pneumoniae
Haemophilus influenzae
Moraxella catarrhalis
What does previous antibiotic therapy select out
organisms like e.coli and staph aureas that are not respiratory infections but part of the normal flora
Is TB detected by gram stain?
No, ZN or Auramine phenol stain
or Acid and Alcohol Fast Bacilli (AAFB) - resist decolorisation by acid or alcohol
needs special culture conditions
When is identification of TB finally possible
once it has fully grown
What gives an accurate diagnosis of lower respiratory tract infection by minimising contamination
bronchial alveolar lavage
Explain a bronchial alveolar lavage procedure
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
What is bronchial alveolar lavage useful in helping to diagnose
ventilator associated pneumonia
When should blood cultures be taken
Any patient with severe sepsis
Patients with bacteraemia due to pneumonia
SEVERE DISEASES
what is the steps in blood culture
Blood inoculated into two bottles containing culture media and incubated
taken to microbiology unit
machine beeps when you have a positive result
post 48 hours nothing found, results = negative
Following positive result of blood culture what steps occur next
day 1: Overnight subculture of sensitivity and identification tests
day 2: full ID, check sensitivity and clinical significance
Why is the clinician contacted by the microbiology unit
to inform the result ensuring proper treatment is given by recommending most efficient antibiotic
What are some example of organisms that aren’t easily cultures
Legionella pneumophila Mycoplasma pneumoniae Chlamydia psittaci (birds) Coxiella burnetti (Q fever) (legit ella my cock burns, chlamydia)
What is a non culturing method for demonstrating the presence of another organism
Specific antigen detection
Where can Legionella and pneumococcal antigens be detected
Urine
viruses in naso-pharyngeal secretions (snot)
Define agglutination
reaction in which particles suspended in a liquid collect into clumps and which occurs especially as a serological response to a specific antibody
What is different ways antigen detection can occur
agglutination
EIAS
Immunofluorescence
How does Immunofluorescence work in antigen detection
location of an antigen in tissues by reaction with an antibody labelled with a fluorescent dye.
What occurs in latex agglutination
latex particles coated in monolocal antibodies and are mixed with clinical specimen in answer, if organism present an agglutination will form
What does EIA stand for
Enzyme Immuno-Assay
What does ELISA stand for
Enzyme Linked Immunosorbent Assay
What are EIA and ELISA both
specific antibody detection test, detects antigen and produced a colour change by enzyme linked on second antibody
The more antigen present in an ELISA results in what
the more colour change
What is the steps in the DNA detection of PCR
DNA opens up by denaturing
Primers attach to complimentary base - anneal
multiple copies then produced as it extends
The primers have what kind of sequence in PCR
short oligonucleotide
When do you know detection is positive in PCR
If primer bind to target = amplified copies of DNA easily detected
What is the disadvantaged of PCR
very sensitive
many false positives due to contamination
How do respiratory diagnoses occur through PCR
respiratory samples collected e.g. through throat/flocked swabs then screened for wide range of respiratory viruses
What is the different respiratory viruses you could be screened against in PCR
Influenza A and B Adenovirus RSV Parainfluenza viruses Metapneumovirus Coronavirus Rhinovirus (in paramount met a rhino, RSVP add corona)
What do serology tests measure
The antibodies in your bloods
What does it mean if IgM is present in a Serological Diagnosis
IgM is a marker of current infection
What does it mean if IgG is present in a Serological Diagnosis
IgG marks previous infection
Why would the total number of antibodies be measured in a Serological Diagnosis
to show the rising titre
Does it take a short or a long time for antibody numbers to rise
long time
What is antibody measurement mostly used for these days
to determine immunity - vaccination response
What is the rising titre
increase in the levels of antibodies over the course of an illness
