Identification of bacteria
Macroscopic examination
· Culture media (specific additives)
· Shape, size, colour and consistency of colony Microscopic examination
· Add “bacteria solution” onto growth media using a wire loop
· Selective enrichment enables specific bacteria to be identified
· Various stains assist identification
· High powered microscope usually required
The Gram stain
· Heat fix bacteria onto a slide and flood with iodine
or crystal violet (blue) then rinse off with alcohol
and safranin
· Gram positive: blue dye retained
· Gram negative: blue dye rinsed away
Biochemical reaction
· Based on the presence/absence of enzymes
· Response to certain chemicals, sugar, etc.
Serological typing
· Based on antigen-antibody reaction (the immune response)
· Distinguishes sub-types of same species
· 2000 different serotypes of salmonella
· Most common is Salmonella enteritidis
Phage typing
· Enables differentiation of same serotype
· Some viruses are able to infect and kill bacteria (bacteriophages)
· They are very selective and can distinguish between bacteria with the same serotype
· Most common is S. Enteritidis PT4
Immunoassay
The use of monoclonal antibodies e.g.
ELISA (Enzyme Linked Immunosorbant Assay)