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20 terms

Microbiology Lab Test

Why are thick or dense smears less likely to provide a good smear preparation for microscopic evaluation?
It will diminish the amount o flight that can pass through making it difficult to see under the microscope.
Why is it essential that smears be air-dried? Why can't they be gently heated over the flame to speed up the drying process?
1. Overheat will denature and rupture the cell wall. 2. excess water on the slides will boil during fixation
Why should you be careful not to overheat the smear during the heat-fixing process?
Overheating will distort the morphology through plasmolysis of the cell wall
Why do you think the presence of grease or dirt on a glass slide will result in a poor smear preparations?
1. Bacteria will attach to the grease or dirt and wash away when staining. 2. It can also diminish the microscopic light making it hard to see the cells.
Why are basic dyes more effective for bacterial staining than acidic dyes?
Basic stains with a positively charge chromogen are preferred because bacterial nucleic acid and certain cell wall components carry a negative charge that strongly attract and binds to the cationic chromogen.
Can simple staining technique be used to identify more than the morphological characteristics of microorganisms? Explain
Yes, the purpose of simple staining is to elucidate the morphology and also arrangement of bacteria cells.
During the performance of the simple staining procedure, you failed to heat fix your E. coli smear preparation. Upon microscopic examination, how would you expect this slide to differ from the correctly prepared slides?
When heat fixing the bacteria, the bacterial proteins are coagulated and fixed to the glass surface. If fail to heat fix, the bacteria will wash away when staining.
During a coffee break, your friend spills coffee on your lab coat and the fabric is discovered. Is this a true biological stain or simply a compound capable of imparting color? Explain your rationale.
Coffee does not contain an auxochrome group which conveys the property of ionization to the chromogen, enabling it to form salts and bind to fibers or tissues.
What are the advantages of differential staining procedure over the simple staining techniques?
The differential staining determine the shape, arrangement, and gram reaction while the simple staining only determine the morphology
Cite the purpose of each following reagents in the differential staining procedure: Primary stain, counterstain, decolorizing agent, mordant.
Primary stain: to impart its color to all cells
Counterstain: Determine gram-positive (retain the purple primary color) or gram-negative (undergo decolorization).
Decolorizing agent: remove excess dye of cell and may or may not remove the primary stain from entire cell or only certain cell structure
Mordant: Increases the cells' affinity for a stain
Why is it essential that the primary stain and the counterstain be of contrasting color?
So it can be distinguished from each other.
Which is the most crucial step in the performance of the Gram staining procedures?
Over-decolorizing will result in the lost of primary stain, causing gram positive to appear negative. Under-d will not completely remove the crystal violet, causing the gram negative to appear gram positive.
Because of snowstorm, your regular laboratory session was canceled and the Gram staining procedure was perform on cultures incubated for a longer period of time. Examination of stained Bacillus Cereus slides revealed a great deal of color variability, ranging from an intense blue to shades of pink. Account for this result.
The cell wall will begins to leak after the cell dies and the stain does not hold as well.
Why is heat necessary in spore staining?
Heat penetrate into the endospore wall. Spores have imperiate coat around them. Coat loosen up the cortex for it to accept the stain.
Explain the function of water in spore staining
It wash off the excess primary stain but not the spore.
You used acid-alcohol as the decolorizing agent
It will removes stain, bacteria, and spores.
You used safranin as the primary stain and malachite green as the counterstain
The cells will stain green and the spore will stain red
You did not apply heat during the application o the primary stain
The stain won't penetrate the spores
Explain the medical significance of a capsule
It prevents the white blood cells to phagocytize the bacteria and increases virulence
Explain the function of copper sulfate in this procedure
It washes the purple primary stain out of the capsular material without removing the stain bound to the cell wall