Using the Laboratory Well

Question 1

what are the 3 main molecular tests?

Answer 1

PCR
MALTI-TOF
whole genome sequencing

Question 2

culture is mainly used for what 2 types of organism and what types of sample can this be used on?

Answer 2

bacteria and fungi
can be used on:
- blood
- swabs from areas
- fluids (pleural, ascetic, CSF etc)
- tissue

Question 3

how are culture samples stored?

Answer 3

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

Question 4

when are samples for blood culture appropriate?

Answer 4

blood cultures for all cases of suspected sepsis

Question 5

when are urine cultures appropriate?

Answer 5

only when clinical symptoms and signs suggest UTI as many people can have asymptomatic bacteruria

Question 6

are routine swabs useful?

Answer 6

no

often just grow colonizing flora rather than causative organism

Question 7

does bacteria in urine always mean a UTI is present?

Answer 7

no

only when symptoms are present

Question 8

serology is the measurement of either what 2 things?

Answer 8

antibody (IgM or IgG)

Antigen

Question 9

what is serology used for?

Answer 9

infection not due to bacteria (mainly viruses)

Question 10

IgM vs IgG on serology?

Answer 10

IgM = recent exposure (first Ig released)
IgG = patient has been exposed at some point, can't tell when

Question 11

give an example of antigens which can be tested for in serology

Answer 11

HBsAg in Hep B

Question 12

give an example of an antibody tested for in serology

Answer 12

EBV IgM

= acute mononucleosis

Question 13

what is PCR?

Answer 13

polymerase chain reaction

technique for making direct copied of DNA using heat stable enzyme (Taq polymerase)

Question 14

how does PCR copy DNA?

Answer 14

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

Question 15

PCR is the main test for detection of what?

Answer 15

viruses (occasionally bacteria)

Question 16

PCR can be used on what samples?

Answer 16

blood (bloodborne infections)

swab or fluid (e.g CSF)

Question 17

what can PCR tell you?

Answer 17

whether organism is present or not

how much is there

Question 18

which is quicker, PCR or culture?

Answer 18

PCR (3-4 hrs)

culture (24-48 hrs)

Question 19

give 4 examples of PCR diagnoses

Answer 19

throat swab = viral resp infections
stool sample = norovirus
CSF = HSV, enterovirus, meningitis
sputum = TB

Question 20

why is PCR an improvement on culture for TB diagnosis?

Answer 20

mycobacterium tuberculosis can take weeks to grow in lab so PCR is far quicker

Question 21

how can PCR be used for monitoring?

Answer 21

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

Question 22

PCR is mainly used for monitoring of what type of infection?

Answer 22

bloodborne viruses

• HIV (persistent -ve = control)
• Hep B (persistent -ve = control)
• Hep C (persistent -ve = cure)

Question 23

what is maldi tof used for?

Answer 23

diagnosing and identifying organism with high sensitivity and specificity

Question 24

2 drawbacks of Maldi tof?

Answer 24

only sensitive if material on plate is all the same organism

wont provide antibiotic susceptibility

Question 25

benefits of whole genome sequencing?

Answer 25

determines entire DNA sequence for organism independent of one or select number of genes
can provide much more information (gene mutations, antibiotic resistance etc)