Cultures
last authored: Feb 2010, David LaPierre
last reviewed:
Introduction
Bacterial cultures are useful for evaluating growth on differential media, testing antibiotic sensitivity and resistance, and selecting colonies for further testing.
- plating
- biochemical tests
- serology
- molecular diagnostics
Plating
Blood agar is the most commonly used plate, growing alomst every organism except Hemophilus. It can also be used to grow fastodious organisms and test for hemolytic capacity.
Chocolate contains extra nutrients and grows Hemophilus.
BH (brain/heart) is used for anerobes.
McKonkey is used to grow gram-negative bacteria and test them for lactose fermentation.
Other plates include pen-strep (for yeast), Mannitol salts (for strep), or OFPBC.
Biochemical Tests
Enzymatic activity can be used to distinguish bacteria. One common mechanism is to examine carbohydrate fermentation. Different sugars include:
- glucose
- lactose
- galactose
- sucrose
Enterobacteriacae (Escherichia, Enterobacter, Shigella, Citrobacter, Samolnella) are all oxidase-negative.
Serology
Serology uses antibodies to determine the presence of specific pathogens.
A slide agglutination test uses known antibodies against an unknown bacteria.
ELISA and Western blotting can also be helpful.
Molecular Diagnostics
Some tests include:
DNA sequencing
Restriction fragment analysis
PCR
DNA chips
 |