Bacterial identification and diagnostics Flashcards
What are growth dependent methods?
Using agar plates containing agar at 1.5-2.0% as a solidifying agent. This acts as a general growth platform.
Selective and differential media help to detect specific species of bacteria
What are inhibitory agents?
Agents which prevent growth of irrelevant bacteria
What is the MacConkey media?
Used for isolation and differentiation of non-fastidious G-rods (pseaudamonas)
Uses crystal violet and bile salts which inhibit most species of gram positive bacteria
What is the PEMBA media?
Selective for Bacillus cereus, with Polymyxin B selectively inhibiting growth of most other bacteria
What is the Baird parker media?
Selective media for staphylococcus aureus using lithium and tellurite
How is haemolysis detected and categorised?
Can be detected as zones of clearing surrounding colonies grown in the presence of insoluble substrates
alpha = partial haemolysis
beta = complete haemolysis
gamma = no haemolysis
What are the 3 types of biochemical tests?
Oxidase, catalase and coagulase tests
Describe the oxidase test
Used to distinguish organisms on the basis of the presence or absence of a respiratory enzyme known as cytochrome C
Dark blue/purple when oxidised (oxidase positive)
Colourless when reduced (oxidase negative)
What is the analytical profile index?
around 20 compartments containing biochemical reagents which can be used to discern more than 550 different species of bacteria
What is PCR
allows replication of a section of target DNA
This allows investigators to confirm a species or specific gene is present
What is the DNA process?
1 - DNA is heated to 94 degrees to separate DNA strands
2 - Primers anneal to complementary sequences at around 65 degrees
3 - Temp increased to 72 degrees for DNA polymerase to synthesise strands
4 - Amplified DNA placed in gel electrophoresis
