What does an MSA plate test for?
Mannitol Salt Agar (MSA) is used to determine if the bacteria is halophilic (salt loving) and if the bacteria can ferment mannitol. If the bacteria is able to grow then it is a halophilic bacteria, due to it’s ability to grow in a high salt environment.
What makes MacConkey Agar differential?
The selective ingredients are the bile salts and the dye, crystal violet which inhibit the growth of Gram-positive bacteria. The differential ingredient is lactose. Fermentation of this sugar results in an acidic pH and causes the pH indicator, neutral red, to turn a bright pinky-red color.
How do you detect E coli on agar?
Presumptive identification of E. coli was made based on its characteristic morphology colony on the selective medium MacConkey agar. Rapid lactose fermenting colonies of E. coli appear dry, donut shaped and dark pink in color and are surrounded with dark pink area of precipitated bile salts.
What does E coli look like on nutrient agar?
coli on Nutrient Agar (NA) 1. They appear large, circular, low convex, grayish, white, moist, smooth, and opaque.
How is E coli transmitted on agar plate?
Plate 50 µL of transformed E. coli/rescue media suspension onto the agar and gently spread over the surface until the liquid is mostly absorbed. The spreading of cells can be done in the same way as the antibiotic, using either a bent micropipette tip or other cell spreading device that fits the plate.
How long does it take for E coli to grow on plate?
24 to 48 hours
How do you plate bacteria on agar?
- Hold loop with bacterial sample parallel to fresh plate.
- Gently rub loop across surface spreading bacteria thinly throughout.
- Flip loop on other side or even gently drag edges across plate if visible bacteria still needs to be delivered.
Why is it important to label agar plates on the bottom and not the lid?
After the culture medium is set, and streaked with the required microbe/stock, the lid is put on and the petri dish is incubated upside down to minimize contamination. So, it is easier to read the label on the bottom. agar plates must be kept with lid on to avoid contamination when not being used.
Why do we invert agar plates?
Petri dishes need to be incubated upside-down to lessen contamination risks from airborne particles landing on them and to prevent the accumulation of water condensation that could disturb or compromise a culture.
How can we prevent agar plate contamination?
Procedure (for the teacher)
- Minimize the time that the agar plate is open to the air during swabbing; be sure to keep fingers out of the plate;
- Incubate plates at room temperature (no higher than 25°C) for 24 hours; higher temperatures or longer incubations may allow for bacterial contaminants to grow;