47. You performed an ELISA test on four patient samples and included the appropr

Question

47. You performed an ELISA test on four patient samples and included the appropriate controls. After the test was done, Patients 1 and 3 were brown and Patients 2 and 4 were clear. Both the positive and negative controls turned brown as well. How would you report these results? a) Patients 1 and 3 are negaitive and patients 2 and 4 are positive b) Patients 1 and 3 are positive and patients 2 and 4 are negative c) The doctor should interpret the results since you are only a lab tech d) These results are invalid and the test needs to be repeated.

21. A patient has been shown to have an overabundance of bacteria from the family Enterobacteriaceae. You perform an IMVIC test series and the results show a positive methyl red test, a negative Voges-Proskauer test and a negative Citrate Utilization test. Which organism is infecting this person? a) Klebsiella pneumoniae b) These results are inconclusive c) Escherichia coli d) Enterobacter aerogenese

23. Which of the following organisms shows carbohydrate fermentation of lactose, dextrose, or sucrose? a) Both Escherichia coli and Enterobacter aerogenes b) Neither Escherichia coli and Enterobacter aerogenes c) Escherichia coli d) Enterobacter aerogenes

48. You cultured a patient's sample and received the following results. Which organism is the patient infected with? Mannitol salt agar: growth and yellow color Phenylethyl alcohol agar: growth a) Escherichia coli b) Staphylococcus aureus c) Streptococcus sanguis d) Enterobacter aerogenese

13. All enteric bacteria, including Escherichia coli, oxidize glucose for their energy needs. In the methyl red (MR) rest, E. coli produce a mixture of fermentation acids. The presence of those acids is detected: a) with the addition of phenol red indicator, the media changes from yellow to red b) with the addition of phenol red indicator, the media changes from red to yellow c) with the addition of methyl red indicator, the media changes from yellow to red d)with the addition of methyl red indicator, the media changes from red to yellow

14. what is the msot important ingredient in the MR-VP media? Hint: it is a carbohydrate. a)fructose b)citrate c)glucose d)tryptophan

Explanation / Answer

47. The answer is d) These results are invalid and the test needs to be repeated.

Both the positive and negative control cannot give the same result. As a positive control gives an indication that how a disease patient sample will give the result and negative control gives an indication how the normal patient reacts to the test.

21. The answer is E.coli. The positive methyl red gives an indication of metabolism through the usage of pyruvate as substrate. Red colour appears if the pH is lower than 4.2.

23. The answer is a) Both Escherichia coli and Enterobacter aerogenes. Carbohydrate fermentation tests detect the ability of microorganisms to ferment a specific carbohydrate. All members of the Enterobacteriaceae family are classified as glucose fermenters because they can metabolise glucose anaerobically.

48. Mannitol salt agar is selective growth media for culturing of Gram-positive bacteria Staphylococcus since the high NaCl levels are inhibitory for other bacteria. Phenyl ethyl alcohol agar is also selective for Gram-positive bacteria. The answer is b) Staphylococcus aureus

13. The answer is b) with the addition of phenol red indicator, the media changes from red to yellow. The methyl red is red in colour and does not change the colour with the presence of acids. It stays red at an acidic pH, but phenol red turns yellow below the pH of 6.8.

14. The answer is c)glucose. In this test, the glucose is the substrate for the growth of the bacteria.

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