1. Give two methods you would use to determine if bacteria have flagella. 2. McC
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Question
1. Give two methods you would use to determine if bacteria have flagella.
2. McConkey agar plates are used to isolate enteric bacteria. It contains bile salts and crystal violet which inhibits the growth of Gram (+) bacteria. The plate also contains lactose and a neutral red pH indicator in order to detect fermentation. Plates were grown at 37°C. (Note: if you choose to answer this question you must answer both part A and B)
A.) What component(s) make the media selective? What component(s) makes it differential?
B.) You inoculate the plate with E. coli, Serratia marcescens, and Staphylococcus epidermidis. E. coli and Serratia marcescens grew, but no growth occurred with the Staphylococcus epidermidis. The E. coli appeared pink in color instead of its usual white and the Serratia was white. What does this tell you about each bacteria?
3. You observe a bacterium with a spirochete morphology. What type of flagella does this microbe have? How do spirochete flagella differ from peritrichous flagella in location and how it moves the microbe?
4. List three structures of the Gram negative cell envelope and their function.
Explanation / Answer
1. There are several method for the identification of flagella structure in the bacteria. Two of them are (1) Darkfield microscopy and (2) Staining technique.
Darkfield microscopy is a simple technique to enhance the contrast of very thin structures without the need for staining.
Staining technique uses a special stain i.e. flagellar stain that stain the bacterial flagella. Crystal violet is used in an alcoholic solution and after staining, the alcohol evaporates, enhancing the presence of the flagella. Flagella will stain purple and should be examined with oil immersion.
2.
A. Bile salt and crystal violet make it selective because both components inhibit the growth of Gram-positive bacteria. Therefore this method can isolate selectively to Gram-negative bacteria. Enteric bacteria can ferment lactose which can be differentiated by adding lactose and neutral red dye will turn the microbe in pink color only to the fermenting lactose microbes. Therefore lactose and neutral red pH indicator makes it differential.
B. E.coli is gram negative bacteria and it is found in intestinal part. After the procedure of the given staining method, the turning of E.coli in pink indicating that it is lactose fermenting gram-negative enteric bacteria.
Serratia marcescens is gram negative bacteria, but it does not ferment lactose and hence it is not stained by neutral red pH indicator and this stain stains only to lactose fermenting bacteria. Therefore this bacteria not stained in pink color.
Staphylococcus epidermidis is a gram positive bacteria, and its growth is inhibited by bile acid ad crystal violet in the media.
3. Spitochete have periplasmic flagella filament that are present between the peptidoglycan and outer layer of the cell membrane. Peritrichous flagella are attached to the all over the cell surface while spirochete is located in between the peptidoglycan and outer membrane of the cell. The spirochete flagella move the bacterium by rotating the bacteria while peritrichous flagella flaments move the bacteria by supporting in swimming.
4. The cell envelop of Gram-negative bacteria consists of phospholipids, lipopolysaccharides (LPS), lipoproteins and surface proteins. The peptidoglycan in the Gram-negative cell wall prevents the cell from osmotic lysis. It is semipermeable nature and helps to retain certain enzymes and prevents some toxic substances.
Lipoproteins add strength to the outer membrane. The surface proteins in the bacterial peptidoglycan carry out a variety of activities as enzymes and also serve as adhesins. Adhesins enable the bacterium to adhere to host calls and other surfaces in order to colonize those cells and resist flushing from the surface.
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