9 Diagnostic Microbiology Flashcards
What is necessary for full and effective treatment?
The more you know about the organism causing the infection the better (species and strain)
What sort of samples can be collected?
Urine (in mid stream)
Blood
Cerebrospinal fluid
Swabs (prostate,up urethra, vaginal etc)
What is essential after the samples have been collected?
Essential that they are stored correctly and transportation must be suitable
How are organisms identified?
Staining (Gram staining) and specific growth medium
What factors need to be considered for the growth of organisms?
Aerobic vs anaerobic
Optimal temperature
Optimal pH
Length of time required for growth
What is a defined medium?
The exact chemicals required for growth are supplied
Undefined medium can contain material from sources such as…
Yeast extract
Proteolysed protein
Gelling agents for agar plates
Sterilised faecal samples
It is unlikely that a collected sample will be pure, why?
Because there will probably be different species in it
What does purification of the pathogen involve?
Differential selective media
Inclusion of antibiotics
What can be used to pick species of interest?
Differences in growth pattern eg morphology and colour
What is mannitol salts agar used for?
Isolation of Staphylococcus aureus, however related species can grow on it
What is so special about the mannitol salts agar?
Contains 7.5% [w/v] NaCl which prevents growth of Gram negative bacteria
What does phenol red on an MSA act as? And what happens during Mannitol fermentation?
Acts as a pH indicator
Mannitol fermentation drops (acidic) the pH which produces yellow zones
What happens when S. aureus uses the Mannitol?
MSA plates become yellow where it grows and other staphylococci remain red
How are bacteria identified phenotypically?
Morphology
Gram staining
Microscopic morphology
Growth on selective/differential medie
