Systems For Detecting Pathogens

Question 1

What is the taxogenic ladder after species?

Answer 1

Strain
Type
Isolate

Question 2

What are the types of pathogens?

Answer 2

Commensal non-pathogen
Zoonotic non-pathogen
Commensal opportunist

Question 3

What is a commensal non-pathogen?

Answer 3

Present but not capable of causing disease in the host

Question 4

What is a zoonotic non-pathogen?

Answer 4

Present but only capable of causing disease in another host

Question 5

What is a commensal opportunist?

Answer 5

Present and capable of causing disease in the host in certain circumstances

Question 6

What is a pathogen?

Answer 6

Microbe capable of causing a specific degree of host damage

Question 7

What is good sample practice?

Answer 7

Sterile sites should be free from contamination
Non-sterile sites require decontamination of normal flora
Samples with high volume or low infected pathogen load require concentration

Question 8

What is direct light microscopy used to detect?

Answer 8

Threadworms, entamoeba histolytica, trichomonas vaginalis, schistosoma mansonii

Question 9

What is direct electron microscopy used for?

Answer 9

Viruses

Question 10

What colour do gram positive bacteria stain?

Answer 10

Blue

Question 11

What colour do gram negative bacteria stain?

Answer 11

Pink

Question 12

Are there bacteria that don’t stain?

Answer 12

Yes (TB for example)

Question 13

What are the types of media?

Answer 13

Non-selective
Semi-selective
Selective growth temperatures

Question 14

What are examples of non-selective media?

Answer 14

Blood, agar

Question 15

What are examples of semi-selective media?

Answer 15

DCA, CLED

Question 16

What are some selective atmospheres?

Answer 16

Aerobic
Microaerophilic
Anaerobic

Question 17

What are the different types of test system in bacteriology?

Answer 17

Media
Selective atmospheres
Selective temperatures
Specific haemolysis of blood

Question 18

What is a phage?

Answer 18

Virus that infect bacteria

Question 19

What is strand displacement amplification?

Answer 19

Essentially PCR

Question 20

What does molecular gene targeting aim to do?

Answer 20

Detect a gene or gene products that are pathogen specific

Question 21

What genes are suitable targets for PCR?

Answer 21

Constitutive 
Virulence
Antibiotic resistance
Pathogenic phenotype 
Repetitive

Question 22

How can you tell if the molecular test for one gene is good enough?

Answer 22

Specificity
Reliability 
Sensitivity
Accuracy
Rapidity

Question 23

How do you do bio-signature profiling?

Answer 23

Mass spectrometry
Isolate organism
Lyse with crystallising matrix
Ionise and detect time of flight for each particle
Calculate daltons for each protein produced
Compare against an archival database

Question 24

What are the advantages of MALDI-TOF profiling?

Answer 24

Rapid and specific identification

Question 25

What are the disadvantages of MALDI-TOF profiling?

Answer 25

Requires pure culture
Requires rigorous calibration and protocol standardisation
Will only identify known profiles

Question 26

What are biomarkers of virulence?

Answer 26

Looking for selected genes or gene products that drive the disease process

Question 27

What are the advantages of serotyping?

Answer 27

Good specificity and sensitivity

Easily automated

Question 28

What are the disadvantages of serotyping?

Answer 28

Slow
Can be in response to previous exposure
Some antibodies are cross-reactive
Virulence is only inferred by biomarker presence
Infected into an animal model can prove virulence

Question 29

What are the advantages of molecular detection methods?

Answer 29

Rapid
Allows fast, accurate treatment
High sensitivity
Can be automated/ used at point of care

Question 30

What are the disadvantages of molecular detection methods?

Answer 30

Expensive
Doesn’t screen for unknown
Needs expertise 
Labour intensive
Possibility of contamination
Complex methods needed