Clinical Microbiology Diagnostic Tests Quiz

The correct method to detect hydrogen sulfide gas production is by using Peptone iron agar deep containing ferrous sulfate, where the presence of hydrogen sulfide is indicated by a black precipitate or no change in color.

The correct answer is Urea broth with phenol red showing a color change to yellow/orange in the presence of urease, which is characteristic of Proteus species.

The correct test for lysine and ornithine decarboxylase involves using Lysine & Ornithine broth with mineral oil and observing for a color change with Bromcresol purple. The incorrect answers are unrelated tests or media used for different purposes in microbiology.

The phenylalanine deaminase test is used to differentiate bacteria based on their ability to produce phenylalanine deaminase enzyme. The correct test involves the use of phenylalanine slants with the addition of 10% ferric chloride. A positive result is indicated by a green color on the surface of the medium, while a negative result shows no color change.

Simmon's citrate agar is used to determine the ability of an organism to use citrate as its sole source of carbon. If the organism is able to utilize citrate, it will produce alkaline byproducts that change the bromthymol blue medium from green to deep blue.

MR-VP broth and Barritt's reagent are specifically designed to detect the presence of acetonin through color changes. Litmus paper, Benedict's solution, and pH indicator strips are not suitable for detecting acetonin.

MR-VP broth is a differential medium used to distinguish between organisms based on their ability to ferment glucose and produce acids. The Methyl Red test is part of the MR-VP broth test, where the presence of acids turns the medium yellow.

The Catalase production test involves adding hydrogen peroxide to a bacterial culture. If bubbling occurs, it indicates the presence of the enzyme catalase which breaks down hydrogen peroxide into water and oxygen. No bubbling suggests the absence of catalase production.

Cytochrome c oxidase activity can be detected by observing the color change when TMPD is added. In the correct answer, TMPD turns purple in the presence of cytochrome c oxidase activity, resulting in a colorless solution. The incorrect answers do not accurately describe the expected color change.

To detect if bacteria can ferment different carbs, a common method involves using Durham tubes with fermentation broth containing specific carbohydrates like glucose, lactose, or sucrose. The presence of a color indicator like phenol red that changes from red to yellow indicates fermentation by the bacteria.

Different bacteria exhibit specific metabolic pathways when breaking down carbohydrates. By using different tests like starch agar, gelatin hydrolysis, sugar fermentation test, and urea hydrolysis test, we can determine the ability of bacteria to break down specific carbohydrates based on the observed reactions.

The presence of a clear zone around bacterial growth on tributyrin agar indicates that the bacteria are able to break down tributyrin, while no clear zone indicates the inability of bacteria to break down tributyrin.

To detect if bacteria can break down gelatin, it is important to observe the behavior of nutrient gelatin specifically in relation to solidifying at cold temperatures. The correct answer highlights the significance of the nutrient gelatin's behavior in the presence of the bacteria mentioned.

The correct way to detect if bacteria can break down casein (C. violaceum) is by observing the presence of a clear zone around bacterial growth on milk agar. This indicates that the bacteria have broken down the casein. Absence of a clear zone indicates that the bacteria cannot break down casein.

Differentiating between bacterial species based on their ability to ferment mannitol can be achieved using specific growth patterns and color changes on selective/differential agar mediums, each with unique indicators and outcomes.

Phenylethyl Alcohol Agar is selective for gram positive bacteria because it inhibits the growth of gram negative bacteria, allowing only gram positive bacteria to grow. MacConkey Agar, Eosin Methylene Blue Agar, and Blood Agar are not selective for gram positive bacteria and may allow the growth of both gram positive and gram negative bacteria.

The correct answer describes the specific characteristics observed when using Hektoen enteric agar to differentiate between gram negative lactose fermenters and non-fermenters.

Eosin Methylene blue agar is commonly used in microbiology for the selection and differentiation of gram-negative bacteria based on their ability to ferment lactose.