Act 5 Flashcards
Unstained bacterial cells are nearly _______ when observed by light microscopy and hence are difficult to see.
transparent
involves spreading a drop of an aqueous suspension of cells on a glass slide allowing it to dry in air, fixing it with gentle heat, and then applying staining reagents
staining
used to make microorganisms more easily seen, to show certain cell structures, or to reveal their chemical nature
dyes
Heat fixing is never used with preparations made from
milk
What is the purpose of fixation?
kill microorganisms
coagulate the protoplasm of the cell and cause it to adhere to the slide
What are the different staining procedures?
simple staining
differential staining
negative staining
gram staining
What is the sample used in simple staining
teeth scrapings
What is the dye used in simple staining?
methylene blue
What is the sample used in negative staining?
hay infusion
What is the dye used in negative staining
nigrosin
What is the dye used in differential staining?
methylene blue
counterstain: carbol fuchsin
What is the sample used in differential staining
cheek scrapings
What is the sample used in Gram staining?
E. Coli
Staphylococcus aureus
What is being detected in Gram staining?
Gram positive and Gram negative bacterias
What are the dyes used in gram staining?
crystal violet
iodine
decolorizer: acetone
safranin solution
Why are the microorganisms in the hay infusion are not stained?
nigrosin is negatively charged thus it is repelled by the negative charge of the surface of the bacteria
What is the practical importance of Gram staining?
Gram staining allows the differentiation of the two major types of bacteria, thus it is essential as it can help by distinguishing root causes of several diseases caused by bacterias.
Why is the steps in Gram staining carefully standardized?
If the procedure is not properly carried, results might not be reliable or accurate.
Why is it necessary to use young culture (24 hr old culture) in gram staining?
Young cultures are required since cell walls deplete over time thus the cell wall of older cultures might produce gram-variable results leading to misleading and unreliable data outcomes.
