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1.20.2.11 - Laboratory Diagnosis for Infectious Disease - Coggle Diagram
1.20.2.11 - Laboratory Diagnosis for Infectious Disease
Koch's Postulates (1884)
the organism must be isolated from a diseased animal and grown in pure culture
the cultured organism should cause disease when introduced into a healthy animal
the organism must be found in all animals suffering from the disease, but not in healthy animals
the organism must be re-isolated from the experimentally infected animal
carriers
typhoid mary
salmonella enteriditis in chickens
e. cloli in cattle, carriers
campylobacter fetus
causes abortion but colonises the parents, abortion is timing specific
agents of infectious disease
ectoparasites
endoparasites
protozoa
prions
virus
fungi
bacteria
Koch's postulates, summary
A range of different diagnostic techniques indetify organisms
culture
metabolism
staining
microscopic examination
antbody-based
ELISA
immunohistochemistry
fluorescent labelling
phage typing
molecular techniques
determination of antibody against pathogens by serology is evidence of exposure to the organism but not of infection
Koch's postulates allow us to distinguish between commensal bacteria and pathogens
stained smears
blood
abscess
culture
gram stain
polychrome methylene blue
Bacillus anthrax
Ziehl Neelson/Acid fast stain
cultural and biochemical characteristics
colony morphology
culture mediums
haemolyisi on blood agar
a-haemolysis
hemoglobin oxidation to methemoglobin in RBCs – green halo
b-haemolysis
complete hamolysis of RBCs – clear halo around colony
oxygen requirements
immunological techniques
serotyping
LPS (O-antigen))
flagellum
staining with specific fluorescent antibodies
biochemical techniques
oxidase test
oxidation-fermentation test
catalase test
decomposition of hydrogen peroxide to water and oxygen, bubbles if positive
catalse is present in many aerobes and facultative anaerobes cause breakdown of hydrogen peroxide
catalase protects bacteria against free radicals produced in the presence of oxygen
phage typing
phage specific for strain (e.g.
Campylobacter
)
phage = virus that can infect bacteria
each phage binds to a different receptor
epidemiology - link to source and spread
strain specific binding and killing plaques with specific phage
molecular techniques
generally PCR based
organisms dont need to be alive
identification of species and strain
link to spreak and source - epidemiology
different bacterial strains will give different band patterns
serology
distinguish from vaccination?
ELISA to detect antibody levels
not indicative of time point of exposure
ELISA - colourimetric change
antibodies produced in response to bacteria - evidence of exposure not infection
summary of bacterial diagnostic tests
A range of different diagnostic techniques identify bacteria
staining
antibody based
fluorescent labelling
immunohistochemistry
ELISA
metabolism
culture
microscopic examination
phage typing
molecular techniques
determination of antibody against pathogens by serology is evidence of exposure to the organism but not of infection
isolation of live virus
viruses require host cells to replicate
costly
time consuming
ethical issues
requires optimal culturing conditions
legal requirements
nucleic acid detection using molecular techniques
epidemiolgoy - spread/source
PCR used to identify viral DNA/RNA in urine/faeces or cells/tissues
accurate and sensitive - results in a few hours
electron microscopy
only a few experts can reliably produce good quality images
good starting point if unknown disease - morphology tells us about viral class
large number of viral partciles need to be present
costly
immunological techniques
antiviral antibodies to detect viral particles
haemagglutination
works as the viruses bind to the receptors on individual cells, linking them together
large number of viral particles required
used to determine the virus concentration from the tissue culture isolate
diagnostic serology
antibodies produced are in response to virus are indicative of exposure not infection
not indicative of time point of exposure
distinguish from vaccination?
summary of viral diagnostic tests
A range of different diagnostic techniques identify viral organisms
antibody based
immunohistochemistry
ELISA
fluorescent labelling
molecular techniques
culture
serology
microscopic examination
determination of antibody against pathogens by serology is evidence of exposure to the organism but not of infection
culture (f)
yeast
mould
DTM plate
difficult to interpret
should have red halo early in growth
fungus will ultimately turn the whole plate red
direct microscopic examination (p/f)
ringworm
malassezia
eggs, and different life cycle stages
faecal samples, blood smears, skin biopsies
sample collection - complex life cycles
histopathological demonstration of fungal hyphae or yeast forms - deep tissue infections (f)
ringowrm hyphen
microsporum canis
serology (p)
toxoplasma
blood tests
summary for diagnostic tests for fungal and protozoan infections
a range of different diagnostic techniques identify fungal and protozoan organisms
antibody based
immunhoistochemistry
ELISA
fluorescent labelling
culture
microscopic examinations
serology
determination of antibody against pathogens by serology is evidence of exposure to the organism but not of infection