Systems for detection of pathogens Flashcards
What are the three definitions of pathogens?
Commensal non-pathogen (in host)
Zoonotic non pathogen (in carrier)
Commensal opportunist( in host )
What is commensal non pathogen ?
Present but not capable of causing disease in the host e.g.
E.coli
Bacteroides thetaiotaomicron ‘good bacteria)
What are zoonotic non-pathogen ?
These are present but only capable of causing disease in another host
What is commensal opportunist ?
Present in capable of causing disease in the host but only in certain circumstances
e.g. Bacteroidise fragilis
Coagulase Negative Staphlyoccucus (CNS)
What is the definition of a pathogen ?
A microbe which is capable of causing a specific degree of host damage
What are some imaging techniques we can use to look at pathogens ?
Light microscope -Big samples
Electron microscope
Immunofluorescent staining with pathogen specific conjugated antibody
What are the advantages of microscopy?
Easy to perform
Rapid screening
Some parasites have specific morphology
Specific immunofluorescence staining possible
What are the disadvantages of Microscopy ?
Not sensitive
e.g. Mycobacterium tuberculosis screening sputum smears requires at least 10,000 organisms per ml to be visualised
General statins are not specific
Labour intensive (expensive)
What are some examples of media used in culture ?
Non-selective media
e.g. blood agar
Horse blood in agar
Semi Selective Media
MacConkey Agar ,DCA,CLED
Selective growth temperatures
Campylobacter species
Outline some selective media
Lactose fermenting /non-lactose fermenting
Aerobic cultures
There are strict obligate aerobes (must grow in aerobic conditions)
What is microaerophilic culture ?
Requiring little free oxygen or lower partial pressure than atmospheric oxygen
Chocolate blood agar
5% CO2
What are anaerobic cultures ?
No oxygen conditions
Grown in aerobic atmosphere
What is a-haemolysis ?
This is partial haemolysis associated with the reduction of red cell haemoglobin.
Appears green
What is beta-haemolysis?
This is complete lysis of red cells in the media around /under colonies
The area will appear lightened and transparent
How does virus culturing differ ?
Viruses are intracellular organisms and don’t grow out of the cell.
Require permissive cell line
Cytopathic effect
Identification
ELISA
