Systems for detection of pathogens 1 Flashcards
What is taxonomy?
Taxonomy is the naming and classifying of organism
What do names of pathogens imply and not include?
• Names only imply capacity for pathogenicity and don’t include an assessment of virulence
What can pathogens be defined as?
Pathogen can be defined as a biological agent that causes disease or illness to its host.
Why is the standard definition of pathogens not the best definition?
○ Not the best definition as some pathogens may be latent or not at a high enough concentration to cause disease
What is a commensal non-pathogen?
• COMMENSAL NON-PATHOGEN is a pathogen which is present but not capable of causing disease in the host
What is a zoonotic non-pathogen?
• ZOONOTIC NON-PATHOGEN is a pathogen which isn’t present but only capable of causing disease in another host
What is a commensal opportunist?
• COMMENSAL OPPORTUNIST is a pathogen which is present and capable of causing disease in the host but only in certain circumstance
What must we make sure when obtaining a sample of the pathogen?
○ 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)
What is light microscopy used to identify?
Light microscopy can be used to quickly and easily identify large samples
What do we use to see viruses instead of a light microscope and why?
• Difficult to see viruses under a light microscope so could instead use fluorescently labelled antibodies which are complementary to viral proteins infecting our cells
What can electron microscopy be used to identify?
Electron microscopy can be used to identify the shape of smaller microorganisms
What is the advantage of using microscopy?
○ Easy to perform
○ Rapid screening
○ Some parasites have specific morphology to look out for
○ Specific immunofluorescence staining possible
What is the disadvantage of using microscopy?
○ 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
What do cultures rely on?
• This relies on the ability of the test system to be able to grow the pathogen
What os the classical methods of cultures?
Classical method: uses agar plates with different electrolytes to grow bacteria which grow quickly and form colonies
Why can viruses not be grown?
• 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
What do we use to grow viruses?
Use cell lines to grow them
What cells is used to grow herpes simplex?
Vero cells used to be used to grow Herpes simplex
What effect does herpes simplex have in cell?
• Herpes simplex has cytopathic effect in cell which induces changes in the way cell grows
What do antibodies produce if it finds a specific antigen?
• Antibody produces colour if it finds its specific antigen on a virus
What are the advantages of using classical systems?
- Cheap and simple
- Sensitive
- Validated specificity as they have gold standards
- Direct in vivo measurements of therapy effectiveness
- Easily archived
What are the disadvantages of using classical system?
- 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
