Clinical and lab diagnosis of infectious diseases Flashcards
Explain Koch’s postulate to identify pathogens
1) The organism must be found in all animals suffering from the disease, but not in healthy animals
2) The organism must be isolated from a diseased animal and grown in pure culture
3) The cultured organism should cause disease when introduced into a healthy animal
4) The organism must be re-isolated from the experimentally infected animal
What is the primary use of Koch’s postulates
demonstrate that a disease is caused by a microorganism
Which of Koch’s postulates are not always achievable
2) The organism must be isolated from a diseased animal and grown in pure culture (some organisms can’t be grown on their own )
3) The cultured organism should cause disease when introduced into a healthy animal (may only cause a disease under specific conditions )
What are the limitations of Koch’s postulate
with regards to the culturability of organisms and the carrier state
What laboratory tests can be used to diagnose bacterial infections
- Stained smears
- Cultural & biochemical characterization
- Biochemical techniques
- Immunological techniques
- Phage typing
- Molecular techniques
- serology
What stains can be used on smears
- Gram stain
- Acid fats stain (Ziehl Neelson)
- Polychrome methylene blue
Which cultural and biochemical characteristics can differentiate between bacteria
- Colony morphology
- culture medium
- oxygen requirements
How does catalase work
Decomposition of hydrogen peroxide to water and oxygen = bubbles if positive
What is a phage
a virus that can infect bacteria
Each phage binds a different receptor
What does phage typing do
helps to identify species and strain of bacteria
What does serology do
Antibodies produced in response to bacteria
shows evidence of exposure not infection
What laboratory tests can be used to diagnose viral infections
- Isolation of live virus
- Nucleic acid detection using molecular techniques
- Electron microscopy
- Immunological techniques
- Haemagglutination
- Diagnostic serology
What are the disadvantages of isolating live virus to diagnose a virus infection
- viruses require the host cell to replicate
- Costly
- time consuming
What are the disadvantages of electron microscopy to diagnose a virus infection
- large number of virus particles need to be present
- very costly
Only very few experts can reliably produce good images
What laboratory tests can be used to diagnose fungal infections
- culture
- Dermatophyte test medium plate
- Direct microscopic examination
- Histopathological demonstration of fungal hyphae or yeast forms
