Systems for detection of pathogens 1

Question 1

What is taxonomy?

Answer 1

Taxonomy is the naming and classifying of organism

Question 2

What do names of pathogens imply and not include?

Answer 2

• Names only imply capacity for pathogenicity and don’t include an assessment of virulence

Question 3

What can pathogens be defined as?

Answer 3

Pathogen can be defined as a biological agent that causes disease or illness to its host.

Question 4

Why is the standard definition of pathogens not the best definition?

Answer 4

○ Not the best definition as some pathogens may be latent or not at a high enough concentration to cause disease

Question 5

What is a commensal non-pathogen?

Answer 5

• COMMENSAL NON-PATHOGEN is a pathogen which is present but not capable of causing disease in the host

Question 6

What is a zoonotic non-pathogen?

Answer 6

• ZOONOTIC NON-PATHOGEN is a pathogen which isn’t present but only capable of causing disease in another host

Question 7

What is a commensal opportunist?

Answer 7

• COMMENSAL OPPORTUNIST is a pathogen which is present and capable of causing disease in the host but only in certain circumstance

Question 8

What must we make sure when obtaining a sample of the pathogen?

Answer 8

○ Sterile sites are free from contamination
○ Non sterile sites require decontamination of normal flora
○ Samples with high volume/relatively low infected pathogen load require concentration (centrifugation, filtering)

Question 9

What is light microscopy used to identify?

Answer 9

Light microscopy can be used to quickly and easily identify large samples

Question 10

What do we use to see viruses instead of a light microscope and why?

Answer 10

• Difficult to see viruses under a light microscope so could instead use fluorescently labelled antibodies which are complementary to viral proteins infecting our cells

Question 11

What can electron microscopy be used to identify?

Answer 11

Electron microscopy can be used to identify the shape of smaller microorganisms

Question 12

What is the advantage of using microscopy?

Answer 12

○ Easy to perform
○ Rapid screening
○ Some parasites have specific morphology to look out for
○ Specific immunofluorescence staining possible

Question 13

What is the disadvantage of using microscopy?

Answer 13

○ Not very sensitive as screening sputum smears needs at least 10 000 organisms per ml to be visualised
○ General stains are not specific
○ Labour intensive hence expensive
○ Needs specialist interpretive expertise therefore becomes even more expensive

Question 14

What do cultures rely on?

Answer 14

• This relies on the ability of the test system to be able to grow the pathogen

Question 15

What os the classical methods of cultures?

Answer 15

Classical method: uses agar plates with different electrolytes to grow bacteria which grow quickly and form colonies

Question 16

Why can viruses not be grown?

Answer 16

• Viruses can’t be grown as they are intracellular organisms and so require host cell mechanisms to divide as they can’t do it alone

Question 17

What do we use to grow viruses?

Answer 17

Use cell lines to grow them

Question 18

What cells is used to grow herpes simplex?

Answer 18

Vero cells used to be used to grow Herpes simplex

Question 19

What effect does herpes simplex have in cell?

Answer 19

• Herpes simplex has cytopathic effect in cell which induces changes in the way cell grows

Question 20

What do antibodies produce if it finds a specific antigen?

Answer 20

• Antibody produces colour if it finds its specific antigen on a virus

Question 21

What are the advantages of using classical systems?

Answer 21

• Cheap and simple
• Sensitive
• Validated specificity as they have gold standards
• Direct in vivo measurements of therapy effectiveness
• Easily archived

Question 22

What are the disadvantages of using classical system?

Answer 22

• Some pathogens cannot be grown
• Some pathogens cannot be differentiated by biochemistry alone
• It is slow as it needs overnight incubation and some pathogens grow too slowly
• Labour intensive hence expensive
• Requires specialist interpretive expertise therefore becomes even more expensive