How do you isolate a pure culture of bacteria?
How do you isolate a pure culture of bacteria?
Simpler methods for isolation of a pure culture include: (i) spread plating on solid agar medium with a glass spreader and (ii) streak plating with a loop. The purpose of spread plating and streak plating is to isolate individual bacterial cells (colony-forming units) on a nutrient medium.
What indicates growth in a broth culture?
Different organisms will exhibit varying growth characteristics in broth. Some organisms will diffuse uniformly throughout the broth; some will sink to the bottom and form a sediment; some will grow in clumps, producing flocculent growth, and some will float on the top of the broth, forming a pellicle.
How streak plating can provide a way of separating bacteria in a mixed culture?
Streak plate technique is used for the isolation into a pure culture of the organisms (mostly bacteria), from a mixed population. The inoculum is streaked over the agar surface in such a way that it “thins out” the bacteria. Some individual bacterial cells are separated and well-spaced from each other.
What is the most important reason to streak for isolation?
As you might guess, the purpose of streaking for isolation is to produce isolated colonies of an organism on an agar plate. This is useful when you need to separate organisms in a mixed culture or when you need to study the colony morphology of an organism.
Why is it desirable that most cultures be inspected after 15 to 18 hours of incubation?
Cultures should be inspected after incubation overnight (18 hours) but reincubation for an extra 24 hours may be indicated when growth is less than expected from the microscopic findings, or when only tiny colonies are present. These colonies are usually present in large numbers, generally more than 20 per plate.
Why do bacterial cultures need to be incubated usually for at least 24 hours?
Why do bacterial cultures need to be incubated, usually for at least 24 hours, before we can see evidence of bacterial growth that can be observed with the unaided eye? They are selective because they allow certain bacteria to grow on it while others do not grow.
Why are cultures collected from the human body usually incubated at 35 to 37 C?
Why are nutrient agar plates incubated at 37 degrees C and Sabouraud agar at 25 degrees C. Both optimum temps. 37 = human body temp = temp at which some of bodies bacteria will grow. – To minimise contaimination from extraneous bacteria.
Why do all cultures being compared have to be incubated at the same temperature?
The primary reason for incubating bacterial cultures at different temperatures is that specific bacteria are adapted to grow best at different temperatures.
Why must the loop be cool before touching it to a culture?
The inoculating loop must be cooled before it touches the surface of the medium. The loop must be cooled to prevent killing the bacteria. If the loop is too hot, it will kill the bacteria and sizzle and melt the media that further promotes contamination.