An Indirect stain is the best way to see: a. details of the shape andclustering
ID: 4734 • Letter: A
Question
An Indirect stain is the best way to see:a. details of the shape andclustering of bacteria.
b. Endospores ofbacteria.
c. thickness of the cell wallof bacteria.
d. number of flagella andpili on bacteria.
e. the size of the nucleus ofa bacteria. To best observe the clustering ofbacteria, you should:
a. use bacteria from a thick film
b. take care not to spreadthe bacteria too much on the slide.
c. from growth on agarsurfaces.
d. use a needle instead of aloop for spreading your bacteria sample.
e. use bacteria from liquidbacteria culture.
An Indirect stain is the best way to see:
a. details of the shape andclustering of bacteria.
b. Endospores ofbacteria.
c. thickness of the cell wallof bacteria.
d. number of flagella andpili on bacteria.
e. the size of the nucleus ofa bacteria. To best observe the clustering ofbacteria, you should:
a. use bacteria from a thick film
b. take care not to spreadthe bacteria too much on the slide.
c. from growth on agarsurfaces.
d. use a needle instead of aloop for spreading your bacteria sample.
e. use bacteria from liquidbacteria culture.
Explanation / Answer
The acidic dye nigrosine will be used to visualize the capsuleor sheath that surrounds some bacteria in a process called negativestaining. Capsules are composed primarily of polysaccharides orglycoproteins and are gelatinous in texture. They are readilydestroyed by heating and hence direct staining methods cannot beutilized. In general, the size and shape of microorganisms is oftenless distorted with indirect staining procedures, especially whensampled from a broth culture. Therefore negative staining is usefulwhenever the morphology of individual bacteria is in question.Morphology can often be determined with confidence with only thehigh dry lens. Consider that this procedure does not necessarilykill the organism, so be careful.
A properly prepared smear accomplishes two things. It causesbacteria to adhere to a slide so that they can be stained andobserved. It also kills them, rendering pathogenic bacteria safe tohandle. An objective in preparing smears is to learn torecognize the correct density of bacteria to place on theslide. Too many, and they overlap each other giving falsepositives or crowding each other to make a mess. Too few, and theycannot be located on the slide.