week 1- clinical samples Flashcards
why are microbiology samples collected and processed
to correctly identify the pathogen, provide a diagnosis and advise on appropriate therapy in time.
what is a contaminant
an microorganism that wasn’t present in the original samples, but has got into the sample during collection, transport or during processing
what can the isolation of a contaminant lead to
wrong diagnosis and inappropriate treatment
how can contamination during collection be avoided
- Cleaning of the collection site, e.g. use of alcohol-based disinfectant on the skin before blood collection.
- Only trained staff collecting samples, e.g. phlebotomist taking blood.
- An appropriate sample being collected, e.g. mid-stream urine (MSU).
- Using only sterile, approved specimen containers
why should samples be taken at an appropriate time
to maximise the chance of organism recovery
why should samples be taken before anti microbial are taken
what can ensure a reliable diagnosis
multiple orthopaedic tissue samples should be taken
how can reliable samples be taken
the appropriate type of sample and multiple samples are required. Taking a sufficient quantity of the sample must be collected
what should be performed on CSF samples
cell count, gram stain and culture
what are the most commonly used specimens containers
sterile universal/pot
faecal or stool specimen pot
general transport swap
what is sterile universal/pot used for
collect samples of:
Mid-stream urine
Pus
Sputum
Tissue biopsies
CSF
what is purpose of transport medium
contains amines
agar to help maintain organism viability
charcoal to absorb toxins
What is the difference between a general transport swab and pernasal swab?
General transport swab:
Has a transport medium
Plastic or wood shaft
Cotton or rayon tip
Used for wounds, throat swabs, high vaginal swab
Pernasal swab:
Also has a transport medium
Has a wire shaft which can bend
Has a fine tip
Swabs the nasopharynx area
What is the requirement for specimens?
They must be fully labelled
Maintained at correct temperature
Delivered on time to the lab
Correctly packaged to avoid leakage etc
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How are specimens transported to the lab?
By porters and couriers - samples are placed in leak proof containers, then in bags, then in boxes
By an air tube system - safe transportation in pneumatic tube systems
What are the 2 categories of infectious substances?
A and B
What is a category A infectious substance?
An infectious substance that when one is exposed to it, it can cause permanent disability, is a life threatening/fatal disease
Example such as ebola, west nile virus
What is a category B infectious substance?
An infectious substance that does not meet the criteria for inclusion in category A.
Examples such as e coli, staph aureus,
Why do we culture samples?
To check for organism presence
To check for more than one organism
To identify the pathogen
Why do we inoculate media?
To isolate single colonies
To detect mixed cultures,
Why do we have more than one agar type?
Because organism have different growth requirements
What are the different types of agar?
Selective agars: Contains antibiotics to prevent the growth of some organisms so only specific organisms can grow.
Differential agars: allows the distinction of different organisms based on the biochemical reactions
what does enrichment media do
‘impair’ the growth of some organisms, but boost the
growth of target organisms
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What is hazard group 1?
A biological agent that is unlikely to cause disease eg soil organism
Handled in an open lab aka containment level 1
What is hazard group 2?
A biological agent that can cause human disease, there is a risk of spreading to the community but there is effective treatment available eg e coli, s aureus
Handled in a containment level 2 lab.
What is hazard group 3?
A biological agent that can cause severe human disease, is a serious hazard, can spread to the community but there is usually effective treatment. eg TB, monkeypox, salmonella
Handled in containment level 3 lab
What is hazard group 4?
A biological agent causing severe harm/disease, a severe hazard to employees, is likely to spread to the community but there is no effective treatment available. eg ebola, Lassa fever, Marburg virus
Handled in containment level 4 labs only containing viruses.
What safety features do containment level 3 labs require/
HEPA (high efficiency particulate air) filtration of exhaust air
lab is sealable
microbiological safety cabinet - MSC
authorised personnel only
What is a class 1 MSC?
open fronted cabinet where air is drawn at a rate to minimise aerosol escape.
Air is filtered by hepa filter
worker is protected but not the work
used for hazard 2 and most hazard 3 pathogens
What is a class 2 MSC?
Open fronted cabinet where working space is flushed down with sterile air = which is hepa filtered
Both worker and work are protected
used for hazard 2 and and for hazard 3 pathogens in some circumstances
What is a class 3 MSC?
totally enclosed cabinet where worker is separated from work via gloves attached to the ports
Air is hepa filtered
high degree of protection to work and worker
suitable for hazard group 3 and 4 pathogens
