Infectious Disease Module 1 Flashcards
What is MIC?
Minimal inhibitor concentration - lowest concentration of antimicrobial that inhibits macroscopic bacterial growth in the lab
- bacterial cultures are grown to a specific
density then inoculated with anti-microbial at
increasing concentration until the
concentration is reached that prevent further
growth - this level is equated to expected
serum levels of dry to predict success
What is the most reliable method for isolating viruses?
PCR
What is gram staining used for?
Differentiating gram postive and negative bacteria
What is the Ziehl-Neelson used for?
Used for acid fast bacteria such as mycobacteria
What is immunohistochemistry/immunocytochemistry used for?
uses labelled monoclonal antibodies to detect microorganism antigen
What is an antigen?
Molecule or molecular structure on virus/bacteria that can interact with Ab or T-cell receptor
What are tests used to detect antigen?
- ELISA - Enzyme linked immunosorbent assay
- IFA - Direct immunofluorescent assay
- Indirect immunofluorescent assay
- Microscopic aggregate assay
- Nucleic-acid detection: development of assays
that can detect DNA and RNA of all classes of
micro-organisms (FISH assays) - PCR - small amounts of DNA can be detected
by amplification- Real time or quantitative PCR
- Takes into account the number of times the
DNA has been copied to get a set amount of
DNA - this helps with antigen load (FIV
infection) - Can be used for RNA detection as well
What are antibody tests used for?
They use serology: evidence of infection, assessment of immune response to infectious organism
Allows detection of antibodies or immunoglobulins that are formed against all classes of infections
When are IgM and IgG antibodies produced?
IgM - produced during early stages of diseases - within 7 days
IgG - follows IgM and takes weeks to increase - there can be a lag before antibodies are found in the blood (seroconversion)
Paired titers may be used to discriminate vaccination against infection
How can antigen based immunoassays be interpreted?
Positive:
- Pathogen present
- Antigen present but no viable organism in sample
- Vaccine antigen present
- Cross reacting antigen present
- Technical error
- Poor specificity test - false positive
Negative
- Pathogen absent
- Antigen present but below level of detection
- Antigen present but in immune complexes
- Technical error
How can antibody based immunoassays be interpreted?
Positive:
- Response to the pathogen (active infection)
- Previous exposure to pathogen
- Previous vaccination
- Technical error
- Poor specificity - false positives
Negative:
- Exposure to the pathogen has no occured
- Too early in disease course - before seroconversion
- Marked immunosuppression
- Techinical error
- Poor sensitivity - false negatives
What is sensitivity?
Proportion or number of animals with the disease that test positive = yields true positive
- Negative results rules out disease
- false negatives: animals that are positive that test negative
What is specificity?
Proportion or number without the disease that test negative
- Positive result rules in
- High specificity - fewer false positives (animals that don’t have disease that test positive)
What is positive predictive value?
probability that given a positive result the patient has the disease
- Don’t by dividing TP by all the animals tested
What is the negative predictive value?
Probability that given a negative result the patient does not have the disease
