13 MALDI-TOF

Question 1

what are the four main categories

Answer 1

1. microscopy
2. culture
3. serology
4. molecular

Question 2

what happens in the diagnostic microbiology lab

Answer 2

• detect pathogen presence
• identification
• antibiotic sensitivity testing
• epidemiology

Question 3

what are diagnostic labs used for

Answer 3

used to advice treatment

Question 4

what are the disadvantages of traditional diagnostics

Answer 4

• time consuming
• expensive
• labour-insensitive
• tests aren’t universal, specific to species
• poor discrimination

Question 5

why is MALDI-TOFT time consuming

Answer 5

patient can’t wait for results to come back, need an educated guess: start with broad spectrum antibiotic at high dose

Question 6

what is MALDI-TOFT replacing

Answer 6

traditional microbiology

Question 7

what happens in MALDI-TOFT analysation

Answer 7

1. take colony from plate
2. smear on stainless steel slide
3. gram +ve need a pre-treatment, -ve do not
4. add matrix and allow to dry
5. load into machine
6. sample exposed to laser
7. molecules are exposed to charge and enter flight tube
8. smallest molecules detected first, largest later as they are heavier
9. generate mass to charge ratio (mass:charge)
10. identify bug, you compare your trace to database library
11. score value determines probability identified right organisms

Question 8

what happens when the sample are exposed to the laser in MALDI-TOFT

Answer 8

vaporises sample, molecules are proteins that are normally abundant in cell e.g. rRNA

Question 9

how many nm is the MALDI-TOFT laser

Answer 9

337nm

Question 10

what is the issue with using urine and serine samples in MALDI-TOFT

Answer 10

contains things other than pathogen

Question 11

how can you overcome the problem with urine and serine in MALDI-TOFT

Answer 11

centrifuge

Question 12

what have case studies found about MALDI-TOFT

Answer 12

quick
cheap
better patient outcomes
time to adjust therapy from strong non-specific to specific AB reduced by 31 hrs
shorter hospital stay

Question 13

what is MALDI-TOFT quicker than

Answer 13

1 day quicker in identifying bacteria compared to traditional methods

Question 14

what is MALDI-TOFT cheaper than

Answer 14

over course of a year cost is halved compared to tadeonal methods

Question 15

what are the advantages of MALDI-TOFT

Answer 15

• Speed
• Simple and cheap
• Broad applicability – yeasts, fungi, bacteria, don’t need to send as many to specialist labs
• Consolidation of identification testing into
• Non-expert identification possible – reduce number of specialist staff

Question 16

what is the overall advantage

Answer 16

reduces costs and turn-around time and improves patient outcomes

Question 17

what are the disadvantages of MALDI-TOFT

Answer 17

• Cheap to run BUT expensive to buy
• Limited database – identification limited, each company who makes the machine save their own database
• Some closely-related organisms cannot be reliably distinguished – shigella and E. coli
• Can’t be used for antimicrobial susceptibility testing