Question 1

Nucleic acid assays are based on the _____ of the organism and are believed to be more accurate.

Accepted Answer

Nucleic acid assays are based on the genotype of the organism, which refers to the genetic makeup of an individual, rather than their observable phenotype (physical characteristics). This is because genetic information cannot be altered by environmental factors and is believed to provide a more accurate representation of an individual or organism. Plasmids and lysogeny are not relevant to nucleic acid assays.

Question 2

If an organism fermented glucose only and utilized peptones, what would the TSI reaction be?

Accepted Answer

The TSI (Triple Sugar Iron) test indicates glucose fermentation with an alkaline slant and an acid butt (alkaline/acid) when only glucose is fermented and peptones are utilized.

Question 3

This test determines if an organism is a delayed lactose fermenter.

Accepted Answer

The ONPG test is used to differentiate between lactose fermenters and delayed lactose fermenters. The test involves using ONPG as a substrate to detect the presence of the enzyme beta-galactosidase, which is necessary for lactose fermentation. If the organism is a delayed lactose fermenter, it will not be able to ferment lactose immediately, but will eventually produce beta-galactosidase and ferment the lactose. The ONPG test allows for early detection of this enzyme, indicating the potential for delayed lactose fermentation.

Question 4

During this process, glucose enters the glycolysis pathway, resulting in the formation of pyruvic acid, which is further oxidized to other acids. What is this process called?

Accepted Answer

Pyruvic acid is further oxidized to other acids through fermentation, which is a process that occurs in the absence of oxygen.

Question 5

A technician is reading the biochemical tests for identifying a particular gram-negative rod. The organism has produced acid, indicated by a color change, in the closed tube only. This indicates that the organism is

Accepted Answer

The fact that the organism produced acid in the closed tube only indicates that it is a fermenter. Fermenters produce acid as a byproduct of glucose metabolism in the absence of oxygen. Oxidizers, on the other hand, use oxygen as the final electron acceptor in their metabolic pathways and do not produce acid. The information provided does not allow for a determination of whether the organism is also an oxidizer or reducer.

Question 6

If a bacterium utilizes lactose or sucrose and produces H₂S, what will the TSI reaction look like?

Accepted Answer

The production of H₂S suggests that the bacterium is capable of fermenting both lactose and sucrose. In TSI agar, if both lactose and sucrose are fermented, it will lead to the production of acid in both the slant and butt, resulting in an acid/acid reaction. The blackening of the butt indicates the production of hydrogen sulfide gas.

Question 7

To inoculate TSI agar or Kligler iron agar (KIA), the laboratory scientist should pick a well-isolated colony with an inoculating needle and

Accepted Answer

The correct method for inoculating TSI or KIA agar is to stab the butt of the agar with the needle almost to the bottom and then streak the slant surface. This allows for the detection of both aerobic and anaerobic growth, as well as gas and hydrogen sulfide production.

Question 8

The initial screening of gram-negative rods is done by testing for the use of this carbohydrate.

Accepted Answer

Lactose fermenting gram-negative rods will produce acid and gas from lactose fermentation, which can be detected through various biochemical tests, such as the MacConkey agar or Triple Sugar Iron (TSI) agar test. Non-lactose fermenting rods will not produce acid or gas from lactose fermentation. Therefore, testing for lactose utilization is a common initial screening for gram-negative rods.

Question 9

When performing the O/F test, one tube is covered with mineral oil and one tube is left uncovered. Why is one tube covered with mineral oil?

Accepted Answer

The tube covered with mineral oil creates an anaerobic environment, which is necessary for detecting the fermentation ability of the microorganism being tested. The absence of oxygen allows for the utilization of an alternative electron acceptor (such as nitrate) during respiration, leading to the production of acid and a color change in the medium. The uncovered tube allows for a control group to compare the results to, as it is exposed to oxygen and should not undergo fermentation.

Question 10

If a bacterium utilizes lactose or sucrose, what will the TSI reaction look like?

Accepted Answer

The TSI (Triple Sugar Iron) test is designed to differentiate bacteria based on their ability to reduce sulfur and ferment carbohydrates. If a bacterium can utilize lactose or sucrose, it will ferment these sugars, producing acid both in the slant (surface) and the butt (bottom) of the medium, leading to an acid/acid (A/A) reaction, which is indicated by yellow coloration in both parts.

Question 11

Bacteria can use carbohydrates by

Accepted Answer

Bacteria can use carbohydrates by oxidizing them through the process of cellular respiration, which generates energy for the cell. Synthesis, reduction, and induction are not directly related to carbohydrate metabolism in bacteria.

Question 12

These bacteria are unable to ferment either lactose or glucose, but they can degrade the peptones present in the TSI agar or KIA aerobically or anaerobically, resulting in the production of alkaline by-products in the slant or deep, respectively, changing the indicator to a deep red color. What kind of bacteria cannot ferment lactose or glucose?

Accepted Answer

Nonfermenting bacilli are bacteria that are unable to ferment lactose or glucose.

Question 13

The chemical reaction for the ONPG test is

Accepted Answer

The ONPG test is used to detect the presence of β-galactosidase enzyme, which is produced by certain bacteria. This enzyme hydrolyzes ONPG into galactose and o-nitrophenol, which is a yellow compound that can be detected by the presence of a yellow color in the test tube. Option A is incorrect because it describes the hydrolysis of lactose, not ONPG. Option B is incorrect because it describes the metabolic pathway for producing acetoin, which is not relevant to the ONPG test. Option D is incorrect because it describes a different chemical reaction that does not involve β-galactosidase or the hydrolysis of ONPG.

Question 14

Other sugars used to differentiate bacteria include all of the following, except

Accepted Answer

Sucralose is an artificial sweetener and is not typically used as a differentiation sugar for bacteria. Raffinose, arabinose, and rhamnose are all commonly used differentiation sugars.

Question 15

Oxidative/fermentative (O/F) basal medium is a medium that will test the oxidative and fermentative capabilities of a microbe. The pH indicator is _____.

Accepted Answer

Oxidative metabolism produces acids which will lower the pH of the medium. Fermentative metabolism produces acids and gas which will also lower the pH of the medium. The pH indicator bromothymol blue changes color from green to blue as the pH increases, making it the best choice for O/F basal medium.

Question 16

Some bacteria are asaccharolytic. This means that these bacteria

Accepted Answer

Asaccharolytic bacteria do not utilize carbohydrates for energy, instead they use other organic molecules such as amino acids or fatty acids.

Question 17

The methyl red test detects metabolic by-products from what pathway?

Accepted Answer

The methyl red test detects the production of acid by bacteria through the mixed acid fermentation pathway. Specifically, it detects the presence of stable acidic end products such as acetate, formate, and lactate which result from the fermentation of glucose.

Question 18

What are the sugars present in triple sugar iron (TSI)?

Accepted Answer

Triple Sugar Iron (TSI) agar contains sucrose, glucose, and lactose as its sugar components, which are utilized to differentiate enteric bacteria based on their ability to ferment these sugars.

Question 19

What chemicals are added to TSI to detect the production of hydrogen sulfide gas?

Accepted Answer

Ferrous sulfate and sodium thiosulfate are added to TSI to detect the production of hydrogen sulfide gas. The presence of hydrogen sulfide gas will react with the ferrous sulfate to form a black precipitate. Sodium thiosulfate is added as a reducing agent to prevent false positive results. The other choices do not contain sodium thiosulfate, which is necessary for accurate results.

Question 20

Biochemical tests are based on the _____ of microorganisms.

Accepted Answer

Biochemical tests look at the observable characteristics of microorganisms, which falls under their phenotype. These tests generally exploit an organism's ability to utilize or produce specific chemicals, such as sugars or amino acids, and provide clues as to the identity of the microbe. The genotype (genetic makeup) of an organism is not directly tested by biochemical assays, although it may influence the organism's phenotype. Plasmids and lysogeny are both specific biological structures or processes and are not directly relevant to biochemical testing.

Quiz 9: Biochemical Identification of Gram-Negative Bacteria

Nucleic acid assays are based on the _____ of the organism and are believed to be more accurate.

If an organism fermented glucose only and utilized peptones, what would the TSI reaction be?

This test determines if an organism is a delayed lactose fermenter.

During this process, glucose enters the glycolysis pathway, resulting in the formation of pyruvic acid, which is further oxidized to other acids. What is this process called?

A technician is reading the biochemical tests for identifying a particular gram-negative rod. The organism has produced acid, indicated by a color change, in the closed tube only. This indicates that the organism is

If a bacterium utilizes lactose or sucrose and produces H₂S, what will the TSI reaction look like?

To inoculate TSI agar or Kligler iron agar (KIA) , the laboratory scientist should pick a well-isolated colony with an inoculating needle and

The initial screening of gram-negative rods is done by testing for the use of this carbohydrate.

When performing the O/F test, one tube is covered with mineral oil and one tube is left uncovered. Why is one tube covered with mineral oil?

If a bacterium utilizes lactose or sucrose, what will the TSI reaction look like?

Bacteria can use carbohydrates by

The chemical reaction for the ONPG test is

Other sugars used to differentiate bacteria include all of the following, except

Oxidative/fermentative (O/F) basal medium is a medium that will test the oxidative and fermentative capabilities of a microbe. The pH indicator is _____.

Some bacteria are asaccharolytic. This means that these bacteria

The methyl red test detects metabolic by-products from what pathway?

What are the sugars present in triple sugar iron (TSI) ?

What chemicals are added to TSI to detect the production of hydrogen sulfide gas?

Biochemical tests are based on the _____ of microorganisms.

Quiz 9: Biochemical Identification of Gram-Negative Bacteria

Nucleic acid assays are based on the _____ of the organism and are believed to be more accurate.

If an organism fermented glucose only and utilized peptones, what would the TSI reaction be?

This test determines if an organism is a delayed lactose fermenter.

During this process, glucose enters the glycolysis pathway, resulting in the formation of pyruvic acid, which is further oxidized to other acids. What is this process called?

A technician is reading the biochemical tests for identifying a particular gram-negative rod. The organism has produced acid, indicated by a color change, in the closed tube only. This indicates that the organism is

If a bacterium utilizes lactose or sucrose and produces H2S, what will the TSI reaction look like?

To inoculate TSI agar or Kligler iron agar (KIA) , the laboratory scientist should pick a well-isolated colony with an inoculating needle and

The initial screening of gram-negative rods is done by testing for the use of this carbohydrate.

When performing the O/F test, one tube is covered with mineral oil and one tube is left uncovered. Why is one tube covered with mineral oil?

If a bacterium utilizes lactose or sucrose, what will the TSI reaction look like?

Bacteria can use carbohydrates by

The chemical reaction for the ONPG test is

Other sugars used to differentiate bacteria include all of the following, except

Oxidative/fermentative (O/F) basal medium is a medium that will test the oxidative and fermentative capabilities of a microbe. The pH indicator is _____.

Some bacteria are asaccharolytic. This means that these bacteria

The methyl red test detects metabolic by-products from what pathway?

What are the sugars present in triple sugar iron (TSI) ?

What chemicals are added to TSI to detect the production of hydrogen sulfide gas?

Biochemical tests are based on the _____ of microorganisms.

If a bacterium utilizes lactose or sucrose and produces H₂S, what will the TSI reaction look like?