L2 - Laboratory Diagnosis of Infection

Question 1

What are the principles of detection?

Answer 1

• detection of whole organism

- detection of component of organism

Question 2

How can you detect a whole organism?

Answer 2

Microscopy

e.g. CFS, meningitis

Question 3

How can you detect a component of an organism?

Answer 3

Antigen
e.g. lateral flow, 96-well

nucleic acid
e.g. probes - unknown & known

Question 4

What are the uses of direct detection?

Answer 4

establishes presence at particular site

epidemiological info

appropriate therapy

fast

Question 5

What are the limitations of direct detection?

Answer 5

no information on:

• antimicrobial susceptibility
• typing

Question 6

What does isolation of the pathogen via culturing enable?

Answer 6

identification
typing (organism relatedness)
susceptibility testing

Question 7

what are requirements for culturing?

Answer 7

culture medium

incubation

Question 8

What are the types of culture media

Answer 8

non-selective media

selective media

indicator media

Question 9

Examples of non-selective media?

Answer 9

blood agar
chocolate agar
nutrient agar

Question 10

What is selective media?

Answer 10

antibiotics
chemicals (NaCl, Bile salts)
special conditions

Question 11

What is indicator media?

Answer 11

Chromogenic agar - more than 1 species

MacConkey - lactose fermenters

Question 12

What are further tests you can carry out on bacteria after growing on media?

Answer 12

Gram stain

Biochemical tests

detection of specific components

Question 13

Which haemolysis is stronger, alpha or beta?

Answer 13

Beta

Question 14

What is a positive result for an oxidase (TMPPD) test?

Answer 14

purple

Question 15

What actually is the oxidase test?

Answer 15

ability to transpire using the ETC

if last cytoplasms is cytoplasms oxidase = purple chemical colour

Question 16

What is the biochemical test which assesses multiple wells of samples?

Answer 16

API E strip

Question 17

What is Maldi-tof?

Answer 17

compares to database of known spectra

produces spectrum of bacterial proteins

fast & cheap

Question 18

What are uses of culturing bacteria?

Answer 18

establishes presence

Allows use of targeted therapy

epidemiolgical information

typing information

Question 19

What are limitations of culturing bacteria?

Answer 19

slower than direct detection

Question 20

What is susceptibility testing?

Answer 20

viable microorganisms

culture in presence of antimicrobial agent

see if conc. is high enough to kill microorganism

Question 21

How is susceptibility testing carried out?

Answer 21

antibiotic discs

zone of clearing/inhibition

Question 22

What are methods of susceptibility testing?

Answer 22

measure zones of inhibition

commercial e-tests ( gives MIC )

breakpoint plates

Question 23

What are uses of susceptibility testing?

Answer 23

inform decisions on targeted antimicrobial therapy

Question 24

What are limitations of susceptibility testing?

Answer 24

correlation between antimicrobial susceptibility in-vitro and clinical response - not absolute

Question 25

What are immunological tests?

Answer 25

detection of immune response to infection:

antibody detection

fourfold rise in titre

Question 26

What are the uses of antibody detection?

Answer 26

confirms exposure

epidemiological info

Question 27

What is the MAIN limitation of antibody detections?

Answer 27

It’s retrospective