Lecture 2 Flashcards
(30 cards)
Why utilize a dx lab? (3)
- To determine if an infectious agent is present at clinically significant levels
- To obtain an etiological dx
- To guide antimicrobial therapy
What are the other functions of a dx lab? (3)
- Disease surveillance - trend/outbreak identification & antimicrobial resistance
- Regulatory - test for reportable diseases
- Research
Colony forming unit
The single organism which gave rise to a clonal pop colony
Why is a colony forming unit of interest?
Provides info on the number of bacteria present
Why is it important to determine the number of bacteria present?
- Establish clinical significance
- To help identify contaminants
- Standardize lab tests
What is an isolate?
A pure culture derived from a single colony
Genetically homogenous
Suitable for additional characterization
How do you determine your culture media?
Based on the target organism
What is selective media?
Used to preferentially isolate particular taxa or organisms possessing a particular phenotype
Contains chemicals to inhibit the growth of non-target organisms
List the selective media from least to most selective (3)
CNA
MacConkey
Campy-BAP
What is differential media?
Exploits unique physiology of particular taxa to produce unique colony morphologies
Differential means that the organism has the ability to breakdown the different ingredient & produce a characteristic change of hemolysis, colour change, black dots etc.
What are 3 differential media?
MacConkey
XLD
CHROMagar
What does CHROMagar ESBL select for? & what does it look like?
3rd generation cephalosporin resistance
Pink colonies = Escherichia coli
Blue colonies = non- Escherichia coli Enterobacteriaceae
White colonies = pseudomonas
What does CHROMagar MRSA select for? & what does it look like?
Selects for methicillin resistance
Pink colonies = MRSA
What does Mannitol Salt Agar select for? & what does it look like?
Selects for NaCl tolerant organisms
Yellow = Staphylococcus aureus
What does Eosin Methylene Blue select for? & what does it look like? - OT
Selects for gram negatives
Metallic green = Escherichia coli
What does Mannitol Salt Agar media differentiate?
Mannitol fermentation
Breaks down mannitol becoming more acidic & causes a pH change
What does Eosin Methylene Blue differentiate? - OT
lactose fermentors
When is liquid media used?
When testing large samples which aren’t playable on media & occasionally used for pure culture
How do we identify bacteria?
biochemical tests
Matrix-assisted laser depolarization/ionization (MALDI-TOF)
What are the biochemical tests used to identify bacteria? (3)
Colour change
Agglutination
Change in consistency of media
What are biocontainment levels for?
Considers the lab procedures which are required to handle the organism safely
What is biocontainment level 1?
Could be safely handed in basic, well functioning lab (organism won’t cause issues)
What is biocontainment level 2?
Requires personal protective equipment
Pathogens with ingestion & inoculation with primary route of exposure
What is biocontainment level 3?
Organisms which may be transmitted by airborne route
Requires additional primary & secondary barriers
