Streak and Spread Plate Methods
What is the purpose of streak plating?
To isolate individual colonies
What does ubiquity of microbes mean?
Microorganisms are found everywhere.
What makes Mannitol Salt Agar selective?
High NaCl concentration (7.5%)
What indicator does MSA use?
Phenol red
To form the Crystal Violet-Iodine complex; a mordant
Why must plates be inverted during incubation?
To prevent condensation from dripping onto the agar
What pattern on a slant looks like "rootlike" branching?
Rhizoid growth
What makes MSA differential?
Mannitol fermentation changing the pH indicator
What are nosocomial infections?
Health care-associated infections
What kind of decolorizer is used in Gram-staining? What about Acid-Fast?
Acetone-alcohol; acid-alcohol
What are attenuated versus virulent strains?
Virulent strains are able to exert its full disease-causing potential while attenuated are weakened
Why are slants useful for long-term culture maintenance?
They provide more surface area and moisture retention.
What makes MacConkey agar selective? What organism does it inhibit?
What indicator is in MAC?
Neutral red
What color are non acid-fast cells after decolorization?
Clear
A colony is a genetically identical cell that originates from a _____.
Colony Forming Unit (CFU)
Which genus exhibits swarming growth?
Proteus
What does Eosin Methylene Blue select for?
Gram (-) bacteria
What are coliforms?
Bacteria that readily ferment lactose to form acids
What stain is used for capsule staining? What type of stain is it?
Congo red stain; acidic stain
For enumeration, how many colonies have to be present for a sample to be considered valid?
25 to 250 colonies
Name all seven characteristics we look at when characterizing colony morphology
Size, Shape, Margin, Elevation, Optical Properties, Consistency, and Surface Texture
What color does E. coli produce on EMB?
Metallic green sheen
What is the pH range for the different colors on MSA plates? What causes these colors?
Yellow below 6.8 pH, red at 7.4 to 8.4, and pink at pH 8.4 and above; the indicator
What do endospores get their resistance from?
tough outer covering made of the protein keratin