Please enable JavaScript.
Coggle requires JavaScript to display documents.
Bacterial Classification & Diagnostics I - Coggle Diagram
Bacterial Classification &
Diagnostics I
Why is identification important?
Understanding patient's diseases
Optimal therapy
Epidemiology
Prevention
Criteria used for classification
Genotype
Phenotype
Phyla are generally based on staining and cell morphology
Taxonomy
Phylum, then Genus and Species are important for organizing cells
There are also subspecies with specific traits, as well as different strains
How is it done?
Microscopy
Growth/culture
Antigenic properties
Antibiotic resistance
Association with host cells (intracellular, etc.)
DNA Sequencing
Clinical Diagnostics
Levels of diagnosis
Differential diagnosis - list of options
Presumptive diagnosis - most likely, first guess
Definitive/confirmatory diagnosis - you know what it is
Treatment generally begins at presumptive diagnosis level (which closely follows differential)
Lab techniques
Sensitivity
Ability to correctly detect pathogen
Specificity
Ability to correctly determine the absence of a pathogen (differentiate from other organisms)
Sometimes screening tests are followed by a confirmatory test
Types of tests
Rapid, definitive tests - strep throat
Complicated series of tests
No specific test needed - UTI
Approach to Diagnosis
Microscopy
Stains
- tell us about cell wall structure
Gram-positive
hold the blue stain in their peptidoglycan wall
Gram-negative
has the blue stain washed out, but are counterstained red
Acid Fast Stain
Acid fast bacteria are wazy and lipid rich with a wall that holds the red acid fast stain. The rest sample is then counterstained to be blue
Staining can sometimes yeild a presumptive diagnosis
Culture
Media
Blood agar
- default because lots of nutrients
Chocolate agar
- cooked blood agar lol
Some fastidious bacteria need cuz can't get inside RBCs
There are special media for special bugs
Anaerobes require extra special media
Some are unculturable - Chlamydia, Rickettsia, etc.
Differential Media
- show a property of the organism so they can be further classified
Blood agar - some organisms cause hemolysis which can be seen on the agar
Selective Media
- kill or inhibit unwanted organisms (useful for contaminated samples)
MacConkey agar is selective for most gram-
Biochemical tests
- used following culture
Catalase
- differentiates staphylococci (+) from streptococci (-); production of oxygenfrom peroxide
Coagulase
- differentiates S. aureus (+) from S. epidermidis (-); coagulation of rabbit plasma
Optochin
- differentiates S. pneumoniae from veridans streptococci; optochin inhibits S. pn.
There are lots of other tests, too, that are more complicated
Immunoassays
- looking for immune response from patient (antibodies)
Looking for antigens in a sample using antibodies as reagents
Polyclonal antisera
is more sensitive, but less specific
Monoclonal antibodies
are less sensitive, but extremely specific
Monoclonal antiserum
- can be useful depending on crossreactivity
ELISA
- most common technique
Western blot
Rapid tests
-
Lateral Flow Immunoassay
COVID tests - low sensitivity
Molecular Methods
PCR
Specific and sensitive cuz PCR be da dopest
MIcroarrays
uses PCR to amplify, but then hybridized to test multiple pathogens at once