Lab Work Flashcards
what microbiological tests can be done on a sample
culture serology molecular tests -PCR -Whole genome sequencing -MALTI-TOF
how is a culture done
samples inoculated directly onto agar plates and incubated
organisms growing on the plate are then identified and tested for antibiotic susceptibility
what samples can you do a culture with
blood swabs fluids (flexural, ascitic, CSF) tissue urine
why do you only ask for cultures when the patient has symptoms of an infection
bc if there are organisms present that aren’t causing symptoms they dont need to be treated as they are just commensals
what is serology
a measure of antigens or antibody in the blood
antibodies confirm that exposure to a pathogen has haoppened
antigen tests are less common but confirm infection
what does the presence of IgM antibodies in the blood mean
the patient has had recent exposure to the pathogen
what does IgG antibodies in the blood mean
the patient has been exposed to the pathogen at some point (could have been years ago_
what is serology used for
useful in infections which aren’t bacterial eg.
viral
protazoae
spirochaetes
what is PCR used for
detects the presence of VIRUSES
how does PCR work
makes direct copies of a section of DNA which can then be visualised and interpreted
tap polymerase denatures and copies DNA through a continuous cycle of heating and cooling
what samples can PCR be used on
blood - for blood born infections
swab/fluid - detects organisms from site of sample
what 2 things can PCR tell
if the organisms is there
how much of it is there
the presence of an organism on a clinically relevant sample will provide a diagnosis
why is PCR useful with a clinical history suggesting TB
Because mycobacterium tuberculosis takes weeks to grow in lab so PCR is much quicker
why is PCR used for monitoring
because it can tell how much of an organism is present so can give:
- indication of how well a treatment is working
- if infection has cleared spontaneously or been cleared by treatment
what conditions is PCR monitoring used for
mainly blood born viruses eg.
HIV - persistent negative blood PCR indicates control
Hep B- persistent negative blood PCR indicated control
Hep C - persistent negative blood PCR indicates cure
what is MALDI-TOF
molecular test to identify organisms which heats samples with layers and passes the ionised particles across a mass spectrometer to give a ‘finger print’ which is compared with data bases
what are the pros/cons of MALDI-TOF
pro: v sensitive at detecting organisms
con: can’t test for antibiotic susceptibility and gets confused if the sample is a picture of different organisms
what is whole genome sequencing
PCR on steroids lol
determines ENTIRE DNA sequence for an organism
provides much more info eg. what mutations is has for antibiotic resistance
useful for studying epidemiology/out breaks
