Laboratory Detection

Question 1

Contemporary micro for CF, what plates

Answer 1

Blood
Chocolate
MacConkey
Burkholderia Cepacia selective agar
Chromagar plates like SAID or pseudomonas ID
- SAID for small colony variants
Fungi plate like Sabouraud agar

For BCC, any gram negs such as stenos or any strange pseudos molecular ID used to confirm as Phenotypic methods are just nnot reliable for these

Question 2

Conventional micro for CF,
what methods are there

Answer 2

Standard ID on MALDI TOF
Susceptibility testing on VITEK
BD MAX Multiplex PCR
Line probe assays for NTB
Gel electrophoresis for atypical PAs (not done anymore)

Question 3

AST for CF

Answer 3

Susceptibiltiy testing on P. aeruginosa isolates associated with early an intermittent colonisation only (no chronic) -> EUCAST

Manual susceptibility testing on P. aeruginosa especially mucoid

Manual susceptibility for all organisms on Burkholderia Cepacia Selective agar -> no breakpoints available for BC

AST is often poorly predictive of clinical outcome especialy in the management of P. aeruginosa

Omissions dont really adversely affect short term clinical outcome

There is a lack of correlation between conventional susceptibility test results and the actual therapeutic success especially in chronic infections

Question 4

Contemporary vs conventional for CF

Answer 4

Based of a crumlin hospital study:
- culture was 82% sensitive while PCR was 93%
- 80 specimens were PCR positive but culture negative, 26 of which were P. aueriginosa => PC has the potential to detect P. aeruginosa earlier than culture

According to a Belfast study it can detect up to 4-17 months earlier

Question 5

PA targets on BD MAX for CF

Answer 5

16s rRNA
gyrB
ecfX
oprL

Question 5

Principle of Line probe assays for NTB mycobacterium in CF

Answer 5

Strip of nitrocellulose with probes all along it
Take organism, extract DNA, amplify up
Add DNA to strip
Targets match to specific nucleotides of the organism
Look for colour change along card

Question 5

BCC targets on the BD Max for CF

Answer 5

hisA
rpsU
recA
16s rRNA

Question 6

Pros and Cons of Molecular for CF

Answer 6

MALDI Doesnt work for a lot of the NLF GNBs though
MALDI cannot speciate BCC

Molecular methods allow us to detect pseudomonas before traaditional culture can
This can be important in preventing chronic infection
- patient will be molecular positive before they will have a positive culture, this allows us to treat the infection early on to prevent it from ever becoming chronic
- better for the long term treatment of the patient

Question 6

BD MAX multiplex PCR for CF

Answer 6

PCR detection of:
- Pseudomonas aeruginosa
- Burkholderia cepacia
- Achromobacter xylosoxidans
- Stenotrophomonas maltophilia

Multi-target approach for BCC
species specific targets for PA

Question 7

Advantages and disadvantages of line probe assays for NTB Myco in CF

Answer 7

It is not a closed system -> risk of infection -> a lot of steps -> not straight forward

Good performance, successfully identifies 92% of MAC and 100% of M. abscessus

Question 8

Clinical tests for TB

Answer 8

Mantoux tuberculin skin test
Chest X ray
Interferon gamma release assay (IFGRA)

Question 10

Lab diagnosis of TB

Answer 10

Isolation of MTC (excluding M. bovis BCG) from a clinical specimen e.g. liquid culture positive

OR

Detection of MTC nucleic acid in a clinical specimen

AND

positive microscopy for AFB

i.e. positive liquid culture or NAAT as well as AFB on smear