Using the Laboratory Well Flashcards
what are the 3 main molecular tests?
PCR
MALTI-TOF
whole genome sequencing
culture is mainly used for what 2 types of organism and what types of sample can this be used on?
bacteria and fungi can be used on: - blood - swabs from areas - fluids (pleural, ascetic, CSF etc) - tissue
how are culture samples stored?
blood = stored in tubes and incubated and then automated machine flags positive bottles
other samples = inoculated directly onto agar plate and incubates and organisms growing on plate then examined/tested
when are samples for blood culture appropriate?
blood cultures for all cases of suspected sepsis
when are urine cultures appropriate?
only when clinical symptoms and signs suggest UTI as many people can have asymptomatic bacteruria
are routine swabs useful?
no
often just grow colonizing flora rather than causative organism
does bacteria in urine always mean a UTI is present?
no
only when symptoms are present
serology is the measurement of either what 2 things?
antibody (IgM or IgG)
Antigen
what is serology used for?
infection not due to bacteria (mainly viruses)
IgM vs IgG on serology?
IgM = recent exposure (first Ig released) IgG = patient has been exposed at some point, can't tell when
give an example of antigens which can be tested for in serology
HBsAg in Hep B
give an example of an antibody tested for in serology
EBV IgM
= acute mononucleosis
what is PCR?
polymerase chain reaction
technique for making direct copied of DNA using heat stable enzyme (Taq polymerase)
how does PCR copy DNA?
primers provide starting point
primers target specific genes of the organism (normally common genes)
repeated cycles of heating and cooling which denatures DNA, binds primers to denatured DNA and begins DNA synthesis
large numbers of copies can then be visualized and interpreted
PCR is the main test for detection of what?
viruses (occasionally bacteria)
PCR can be used on what samples?
blood (bloodborne infections)
swab or fluid (e.g CSF)
what can PCR tell you?
whether organism is present or not
how much is there
which is quicker, PCR or culture?
PCR (3-4 hrs)
culture (24-48 hrs)
give 4 examples of PCR diagnoses
throat swab = viral resp infections
stool sample = norovirus
CSF = HSV, enterovirus, meningitis
sputum = TB
why is PCR an improvement on culture for TB diagnosis?
mycobacterium tuberculosis can take weeks to grow in lab so PCR is far quicker
how can PCR be used for monitoring?
can tell you how much of organism is present, so monitoring PCR level provides how well treatment is working and if infection has cleared spontaneously or been cured with treatment
PCR is mainly used for monitoring of what type of infection?
bloodborne viruses
- HIV (persistent -ve = control)
- Hep B (persistent -ve = control)
- Hep C (persistent -ve = cure)
what is maldi tof used for?
diagnosing and identifying organism with high sensitivity and specificity
2 drawbacks of Maldi tof?
only sensitive if material on plate is all the same organism
wont provide antibiotic susceptibility
benefits of whole genome sequencing?
determines entire DNA sequence for organism independent of one or select number of genes
can provide much more information (gene mutations, antibiotic resistance etc)
