Diagnosis of Infectious Diseases Flashcards
What is a pathogen?
Infectious agents which cause disease (bacteria, viruses, protozoa, prions)
Name Koch’s postulates
- reg. found in disease lesions
- may be isolated in pure culture on artificial medium (agar not animal)
- inoculation of culture into experimental animals produces similar disease
- may be recovered from lesions in above animals
What is the exception to Koch’s postulates?
Mycobacterium leprae (takes 20yrs to manifest)
What sort of specimens can we collect?
swabs, urine, faeces, sputum, CSF, blood (culture), blood (serum)
When is the best time to collect specimens?
before antibiotics, but depends on disease (e.g. malria taken at spiking fever)
What happens to a specimen under macroscopic investigation?
look for-
odour, mucus or blood in stool, pus in sputum (indicates infection) cloudiness in CSF and urine indicates infection.
Serology - what do we look for?
antibody response to organism over a couple of weeks.
How can we do this?
agglutination, immunofluoresence, complement fixation, ELISA
Why is PCR desirable for determining outbreaks?
- quick results
- e.g. for identifying TB outbreaks where quick results are desirable
- e.g cholera toxins in faeces
Name 3 non selective media to culture on
- blood agar (but selective for haemolytic strep)
- chocolate agar(but selective for genital specimens)
- liquid media such as blood cultures
Name 3 selective media to culture on
- mackonkey agar (not very)
- mannitol salt
- XLD (shigella) red agar
- HE (salmonella) blue agar
What media would be chosen for a wound?
- both selective and non selective
- blood grows most pathogens
- mannitol salt if staphs suspected
- mackonkey if wound abdominal
Which bacteria grows red on MacKonkey agar?
Escherichia coli
What 2 kinds of agar do most respiratory pathogens grown on?
blood and chocolate
