PMB: Diagnostic Microbiology 9 Flashcards
Why is it important to be able to identify the causative organism?
To allow for full and effective treatment to occur
To identify the pathogen it is essential to collect a suitable specimen
What are examples of possible samples?
It is important to take the correct sample. Some include:
- Blood
- CSF
- sputum
- Urine mid stream
- pus or skin
- hair
- nails
- swabs (vignal, prostate)
As well as collection of the samples, what are other important considerations?
If the sample is a blood sample what else is required?
- It is important to store the sample correctly e.g. fridge, away from heat?
- It is also important to transport the sample suitabily
- Detailed and accurate information must be recorded and MUST be accomapanied with the sample
If a blood sample, an anti-coagulant is required
What are examples of information required to be recorded and send with the sample?
- Patient info:
- DOB, Name, Add
- Date and time of collection of sample
- What test is required
- Storage instuctions
- Senders info
When should samples be analysed and what order?
Samples should aim to be analysed as soon as possible without delay after arrival of the sample. However, samples should be priotized. Most urgent should occur first (e.g. life threating)
What are examples of some techniques used to identify bacteria?
- Gram staining
- Attempting to grow the organism on specific growth medium - tho as some medium can be selective with what they grow some info is required on the organism
What are examples of different media growth factors effecting bacterial growth
- Optimum temperature
- Optimum pH
- Anaerobic vs aerobic
- Length of time to grow
- Some medium are highly specific for organisms they can grow and some are not so specific. Some organisms are highly specific for growth medium (Helicobatar Pylon) and some are less specific (pseudomonas aeruginosa)
What is the difference betwee defined and undefined medium?
Defined - purified chemicals (exactly known)
Undefined - some chemicals not purified
What are examples of material from undefined media?
- Yeast extracts
- Proteolysed protein
- Gelling agents for agar plates
- Sterilised faecal samples
Discuss selective and differential media
It is unlikely that the sample collected will be pure, there will probally be several different species in it.
The organism is studied better if it is purified or at least enriched. This can be done using various methods for example differnetial selective media or inclusion of an AB
Often related specieswill grow on the same medium, howveer differences in groth patterns can be used to pick the species of interest
- What is an example of a media which can grow several organisms?
- What is it made of? How does this effect the species of organisms which can grow?
- MSA (mannitol salt agar)
- Made from 7.5% w/v NaCl. The high concentration of Na+ prevents the growth of Gram negative bacteria
- What can be included in the MSA which helps identify species? How does this work?
- Give an example of a species it can be used to identify
- Phenol red can be added. This is a pH indicator which changes colour from red to yellow when the manntiol ferminates and hence pH drops
- Although other sta[hylococcol can grow on MSA, only S.Aurues causes the fermintation of Mannitol therefore a yellow colour to be produced
What approach is the previous process an example off?
Using chromogenic media as an approach to entich and then screen species of intersest
- What is phenotypic identification?
- What are examples of different characterisitics that can be looked at?
- What does this technique rely on?
- Screening bacteria based off phenyotypic characterisitics. A range of traits can be used
- Examples:
- Form of colonies
- Elevation of colonies
- Shape of colonies at margins
- Colony morphology
- Gram staining
- Microscopic morphology
- Cell association / aggregation
- Grow on selective / differential media
- Biochemical / metabolic profile
- Relies on uniformity of colonies
What is biochemical phenyotype?
Once pure cultures of the clinical isolate have been grown, biochemical phenotype can then be established. Simple tests are undertaken to examine for the presence of specific enzymes. An example is catalase, which breaks down H2O2, that distinguishes Staphylococcus sp. (+) from Streptococcus sp. (-).
