System for Detection of Pathogens 1 and 2 Flashcards
Recap the way that we classify all organisms - taxonomy
How many mycobacteria (a genus) are obligate human pathogens?
3
Name the mycobacteria that are obligate human pathogens
- M. tuberculosis
- M. leprae
- M. ulcerans
Explain what a commensal non pathogen is
Present but not capable of causing disease in the host
Explain what a Zoonotic non pathogen is
Present but only capable of causing disease in another host
Explain what a commensal opportunist is
Present and capable of causing disease in the host but only in certain circumstances
How can we define a pathogen?
A microbe capable of causing a specific degree of host damage
- does not HAVE to cause damage
Why might samples not come back as positive for a pathogen when they should be?
- sterile sites (like blood) need to be free from contamination
- non-sterile sites require decontamination of normal flora
- samples with high volume or low pathogen load require concentration by centrifugation or filtering
Do all pathogen samples need to be cultured?
No
Apart from gram staining, what might we look for in a bacterium?
- capsule
- spores formation (anthrax) - also where they are on the bacterium
- immunofluorescence and other tests
What is meant by non-selective vs semi-selective media on an agar plate?
These are mediums that only grow specific organisms
- Non Selective Media
- e.g. Blood agar
- Semi selective media
- e.g. MacConkey Agar, DCA, CLED
What is an aerobic culture?
A culture in oxygen - you can also do an anearobic culture which does not have any oxygen (or CO2?) at all
What type of bacteria tend to grow in anaerobic cultures?
Gut bacteria
e.g Clostridium tetani, Clostrium botulinum, Clostridium difficile, Bacteroides fragilis
What is a microaerophillic culture - what kind of bacteria can grow?
This is growing in CO2 - so respiratory pathogens will grow, including gonorrhoeah and meningitis
Give an example of a bacteria type that we can identify by growing it at the specific temperature of 42 degrees
Campylobacter
Aside from selectiveness of media on agar plate, name other ways that we can identify bacteria by culturing it from a swab (not genotyping)
- we can also use selective growth temperatures to do this
- we can also do this by the environment (so, like, oxygen content)
- specific haemolysis of blood for strep
- metabolic testing (how it uses sugars)
What is phage testing?
bacteriphages are very specific to certain bacteria and only lyse certain bacteria - so we can test if the bacterium lyses in the presence of a specific phage
- this will not identify it but will phage type
What is serotyping?
Serotyping is a subtyping test based on differences in microbial (e.g. viral or bacterial) surfaces Serology refers to the antibodies that form because of a viral or bacterial infection.
- is testing the outer surface!
What is meant by molecular gene targeting in this context of detection of pathogens?
Where we aim to detect a gene or gene product that is specific to the pathogen
Name a way that we can do molecular gene targeting in this context (detection of pathogens)
- PCR (polymerase chain reaction)
NAAT (nucleic acid amplification techniques) - PCR is a type of NAAT
What is strand displacement amplification?
This is another type of amplification that is slightly different to PCR - this is also a type of NAAT
What is MALDI-TOF?
- Matrix Assisted Laser Desorption Ionization-Time-of-Flight
How does MALDI-TOF work?
Breaks up the bacterium with lasers and other means and measures the ‘time of flight’ of the different components and produces a signature specific to the bacterium species
How can we use MALDI-TOF?
We can compare the signatures of an unknown bacterium to known profiles
Name some advantages and disadvantages of MALDI TOF profiling
Advantages
- Rapid
- Specific Identification
Disadvantages
- Requires pure culture
- Requires rigorous calibration and protocol standardisation
- Will only identify known profiles
What is metabolic profiling?
