Diagnostic Flashcards
What are the principles for sample collection
- Specimens obtained aseptically representative of disease
- A sufficient quantity of material
- Specimens collected prior to antimicrobial therapy
- If cultures not immediately initiated must be refrigerated
What needs to be on a sample submission form
- Case history - clinical signs previous treatment ect.
- Required tests - what does clinician want to know
- Sample type - which is most appropriate urine blood ect.
What does microscope observation tell us and why is it good
Cost effective, rapid, shows presence of bacteria/fungi, number of organisms, can check morphological characteristics and stain - gram positive, provides info on host cellular response.
What stain can we use for fungal identification
KOH 10% with Parker blue acts as a clearing agent, when Parker ink is added the fungal spores take up the ink and appear blue-violet
How to use microscopic observation in virus
Pox inclusion is characteristic of a virus. Only other way is electron microscope
What does bacterial culture aim to achieve
- Isolation of organism in pure culture inoculating the specimen onto appropriate artificial culture media
- Identification by microscopic examination, biochemical reactions, state of the art techniques
- Antimicrobial susceptibility testing after growing in pure culture
What are the different types of media
- Enrichment media - supplemented by blood or other nutrients to encourage growth
- Differential media - distinguish between different bacteria on basis of their biological characteristics
- Selective media - favour growth of particular microorganisms and inhibit growth of others
When using 5% sheep blood agar what will u see
Non-haemolytic the agar stays red.
Beta-haemolytic the agar turns yellow.
As some bacteria secrete enzymes that lyse the erythrocytes in agar producing zones of haemolysis
What happens with gram staining
Stages = fixation, crystal violet, iodine treatment, decolorisation, counter stain with Safranin.
Gram positive stop at crystal violet stage and stay purple
Gram negative go all the way to the end and go pink
What does the oxidase test for and show
To determine the presence or absence of specific metabolic enzymes in an isolate. Here is to test for the presence of cytochrome C oxidase, this enzyme reduces TMOD a redox die
Oxidase positive = dark blue/purple
Oxidase negative = colourless
What does the catalase test check for and show
Detects for the presence of the catalase enzyme. If present the external hydrogen peroxide is Brocken down to oxygen and water. Seen as bubbles
Summary of what can we use to identify bacteria
Oxygen requirements
Culture characteristics
Staining properties
Microscopic morphology
Biochemical reactions
MALDI-TOF skips steps can do many at once
Once identified what do we test for
Antimicrobial resistance
Qualitative methods - disc diffusion. Disc impregnated with antimicrobial resistance agents are placed onto the agar leave over night to measure zones of inhibition.
Bacteria can be susceptible and inhibited so can be treated with normal, dose of antibiotic . Or resistant which means the infection could not be treated with normal dose. Or it can be an intermediate which is a buffer zone to avoid misinterpretation
How do viruses differ to bacteria
Obligate intracellular organisms (tissue cell cultures, embryonate eggs, experimental animals)
Need specialist lab to grow
Must inhibit bacterial growth
Not all virus grow in culture
Takes a long time very labour intensive
What effects might we see if a virus is present in culture
Rounding of cells
Syncytia
Inclusion bodies
What is viral haemagglutination
When virus clump red blood cells preventing them from settling at the bottom of a well
Viral glycoproteins cause this - hemagglutinins
How can we obtain a sample off a fungal infection
Plucking hairs from lesions
Toothbrush
Skin scrapings
Exudates
Biopsies
How is fungi cultured
Sabouraud Dextrose Agar (SDA) low pH (5.5) which inhibits the growth of most bacteria. Incubated at 25 degrees and 35 degrees for 1-3 weeks.
Fungal identification is based off macroscopic and microscopic morphology
What is an indirect method of diagnosing ring worm (Microsporum canis)
UV fluorescence. Some fungi produce metabolites that fluoresce a green colour
How can we use an Antibody Antigen test
- Known antigen added to detect specific antibodies in animal e.g. elisa
- Known antibodies to detect bacterial or viral antigens e.g. immunofluorescent antigen test
What is a serological test and what can it detect
- The test detects for the presence of antibodies
So see if the animal has ongoing infection, past exposure to a pathogen, maternally derived antibodies or been vaccinated
Examples = Brucella canis or FIV
What is a delayed hypersensitivity reaction
Skin tuberculin test for bovine TB.
The intradermal injection of bovine TB or purified protein derivative. Then follows subsequent swelling at the site of injection 72 hours later
Positive test = an increase in 4mm in skin fold thickness in 72 hours
What are the advantages and disadvantages of PCR
Advantages = very sensitive, detects microorganisms that are unculturable or slow growing, faster result
Disadvantages = susceptibility of contamination, failure to differentiate live and dead organisms
What is PCR used for
Mycoplasmas
Mycobacteria
Spirochetes
Viruses
Rapid detection of MRSA
