Lab Exam 2 Connect

MIO

"S" refers to sulfide (H2S) production. "I" refers to indole production, which results from tryptophan degradation. "M" refers to motility.

You have inoculated an MIO tube and 24 hours later have recorded the following results. The medium is purple, turbid throughout, and there is no red ring when you add Kovak's reagent. Indicate which of the following represent the correct interpretation of these results. (Check all that apply)

- Indole - - motile - Ornithine decarboxylation +

An organism may produce H2S but not turn the butt yellow.

False

Hydrogen peroxide and the superoxide radical are toxic because they reduce biochemicals and make them nonfunctional.

False

Lactose is added to malonate broth to promote growth of organisms that otherwise are slow to respond.

False

What is the name of the reagent used for the oxidase test?

tetramethyl-p-phenylenediamine

A positive citrate test is indicated by a color change of a citrate slant from blue to green.

False. A positive citrate test is detected by a color change of the citrate slant from green to blue.

The cytochrome oxidase enzyme is a key enzyme catalyzing reactions in the lactic acid fermentation pathway.

False. Cytochrome oxidase functions in the electron transport chain, a component of the aerobic respiration pathway.

determine the Gram stain morphology

False. Gram stain morphology alone is never enough to identify bacteria to the genus and species levels, since multiple bacteria share the same gram stain morphology.

All bacteria produce gas when they ferment

False. Some bacteria use fermentation pathways that result in gas production while others do not and this information can be helpful in the identification process. The Durham tube makes it possible to detect whether gas is produced.

The oxidase test requires the use of a reagent called Kovac's reagent.

False. The oxidase test requires the use of reagent known as oxidase reagent, or tetramethyl-p-phenylenediamine. Kovac's reagent is used for detecting indole production.

TSIA - Red Slant / Yellow Butt

Glucose fermentation with acid production. Proteins catabolized aerobically

You have inoculated an LIA slant with an unknown bacteria. The next day, the butt is yellow and the slant is purple. Choose all of the reults that can be determined with this information.

Glucose was utilized

The identification of an unknown bacterial isolate is based on (Check all that apply)

Gram stain morphology, results of standard biochemical tests, preexisting morphological and biochemical data collected for a large number of previously identified bacterial species

Which of the following biochemical traits can be determined from observing growth of colonies on MacConkey agar?

ability to ferment lactose

What is indicated by a color change of a phenol red glucose broth from red to yellow?

acid was produced

Bacterial fermentation of sugars usually results in ___________ end products whereas breakdown of proteins and amino acids results in the formation of __________ end products.

acidic....alkaline

Urea hydrolysis results in the production of...

alkaline end products (NH3)

Hydrolysis of urea results in

alkaline end products.

What are the products of urea hydrolysis?

ammonia and carbon dioxide

The presence of urease is detected by

an increase in pH causing a color change of a phenol red indicator to bright pink.

The cytochrome oxidase enzyme detected by the oxidase test functions within the cell as part of:

the electron transport chain

Tryptophan hydrolysis results in

the production of indole

What is the role of the crystal violet and bile salts in MacConkey agar?

these ingredients make MacConkey selective by inhibiting gram positive bacteria

Once an unknown bacterium has been isolated in pure culture, what is the first step in the identification process?

determine the Gram stain morphology

Eosin-methylene blue agar, or EMB, is a commonly used bacteriological medium for growing gram-negative bacteria from complex environments. It contains two dyes, eosin and methylene blue, as well as the sugar lactose. Eosin is a pH indicator that changes color when the medium is acidic, while methylene blue inhibits the growth of most gram-positive bacteria. If an organism consumes lactose, acid will be produced, causing the bacterial colonies to change color. Based upon this description, this medium is ______.

differential and selective

TSIA - Yellow Slant / Yellow Butt

glucose and lactose and/or sucrose fermentation with acid accumulation in slant and butt

What is indicated if the phenol red glucose broth stays red throughout incubation?

glucose is not fermented

Which of the following will form pink colonies on MacConkey agar?

lactose fermenters

What is the role of ammonium salts in the citrate agar?

nitrogen source

If a colony is selected with a swab and the addition of oxidase reagent results in no color change, how is this result interpretted?

oxidase negative

What is the role of phenol red in the urea medium?

pH indicator

What is the role of neutral red in MacConkey agar?

pH indicator. Neutral red is the pH indicator which helps make this medium differential.

TSIA red slant/ no change in butt

-No fermentation. Peptone catabolized aerobically with alkaline products

Select the correct statements about MacConkey agar. (Check all that apply)

-The selective ingredients in MacConkey agar are crystal violet and bile salts. - The growth of Gram positive bacteria is inhibited on MacConkey agar. - Most Gram negative bacilli grow well on MacConkey agar. - The differential ingredients in MacConkey agar include lactose and neutral red. - Lactose-fermenting Gram negative bacilli will form pink-purple colonies on MacConkey agar.

A phenol red glucose broth with a Durham tube can detect (Check all that apply.)

Acid production, glucose fermentation, production of gas

Bacterial fermentation of sugars usually results in ___________ end products whereas breakdown of proteins and amino acids results in the formation of __________ end products. Multiple Choice

Acidic, alkaline

What color will indicate a positive urease test?

Bright, hot pink

Select the type of media where the chemical composition is precisely known.

Defined

In your microbiology lab, your class is identifying bacteria. You are using dichotomous keys to aid in the identification process using the data from a variety of biochemical tests. What problems do you foresee in this procedure?

If you misread a biochemical test or write down the wrong result, the key will likely take you to an alternative organism that is not your unknown bacterium.

What must be added to MIO medium to detect tryptophan hydrolysis?

Kovac's reagent

What can be detected by using MIO medium? (Check all that apply.)

Motility, mannitol fermentation, ornithine decarboxylation

If you add hydrogen peroxide to a bacterial colony and no bubbles appear, you could have a bacterial species from which of the following groups?

Streptococcaceae

A microbiologist inoculates Staphylococcus epidermidis and Escherichia coli into a culture medium. Following incubation, only the E. coli grows in the culture. What is the most likely explanation?

The culture medium was selective.

A phenol red glucose broth with a Durham tube has been inoculated and incubated. After 48 hours, the broth is turbid and bright yellow and approximately half of the contents of the Durham tube have been displaced with gas. Interpret these results.

The organism is fermenting glucose with gas production.

You have inoculated a tube of MIO medium and after incubation, the medium remained clear and you can only see growth in the inoculation stab. What does this indicate?

The organism is nonmotile

A selective medium contains one or more substances that inhibit growth of some microbes to facilitate the growth of other desired microbes.

True

Choose the statement that best describes most enzymatic reaction results observed in the biochemical testing of microbial specimens.

Usually visualized by a color change

If you inoculated a TSIA slant with Edwardsiella which only ferments glucose and produces H2S, what would your results be?

black butt, red slant

What will be the color of the medium if the bacterial isolate can utilize citrate as its sole carbon source?

blue

What is the carbon source in citrate agar?

citrate

How would a result be reported if the organism does not grow on citrate agar and the color stays green?

citrate negative

What is the role of the Durham tube?

collect gas produced during fermentation

Malonate is similar enough to succinate to replace it as a substrate. This is an example of:

competitive inhibition

TSIA- red slant/ black butt

production of hydrogen sulfide

What is the purpose of the enzyme lysine decarboxylase?

remove the carboxyl group from the amino acid lysine

Which terms apply to MacConkey agar?

selective and differential

How is Triple Sugar Iron Agar inoculated?

stabbing the butt with an inoculating loop and streaking the slant