Question

OBSERVATIONS Specimen: 24-hour-old Bacillus cereus Specimen: five-day-old Bacillus cereus Total Magnification: Total Magnification: X Endospores? Endospores? х Morphology: Morphology: Size Range: Size Range:

bacterial structural staining
(microbiology lab )

Answer 1

Bacillus cereus is a gram positive, rod shaped bacterium that produces endospores during adverse conditions. The following experiment is of selective endospore staining. In endospore staining, the primary stain used is malachite green that stains both the vegetative cells and the spores. The slide is then washed with water and then the counter stain saffranin is added that stains the cells pink in color while the spores will retain their green colour.

The endospores are of 3 types- Terminal, Sub terminal or central. When observed under the microscope on observation it can be seen that the rod cells will be pink and the spores are dark green in colour. A 1 day old culture may or may not have many endospores because the nutrients are plentily available and there are no adverse conditions.Hence on performing this experiment to a 1 day old culture there will be no spores usually or very very few of them if at all present which is rare. But when compared to a 5 day old culture, there will be many spores as the nutrients have started to deplete and the cells are starved.They get into the doramant stage and form the spores.

After the slide is prepared the cells must be observed under 100X with oil immersion.We will be able to distinguish the cells from the spores and the rod shaped bacterium.

The observation will be as follows-

total magnification= power of objective(100X)* power of eyepiece(10X).

Vegetative cel Endospore 1 day old Culture day Old Culture 10x * 100x = 1000x - 10x * 100x=1000x 16. 1 Total Magnification Endospores Morpholesy. Size Range - Rod shaped Red shaped. 10fm 10pm.