Skip to main content
Ch. 10 - Classification of Microorganisms
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
All textbooksTortora 14th EditionCh. 10 - Classification of MicroorganismsProblem 5
Chapter 10, Problem 5

Use the key in the Clinical Focus box to identify the gram-negative, oxidase-positive rod causing pneumonia in a sea otter. It is H2S-positive, indole-negative, and urease-positive.

Verified step by step guidance
1
Review the Clinical Focus key to understand the characteristics used for bacterial identification: gram-negative, oxidase-positive rods.
Note the biochemical test results given: H₂S-positive, indole-negative, and urease-positive. These tests help differentiate among gram-negative rods.
Recall that H₂S production is detected by black precipitate formation on specific media, indicating the bacterium produces hydrogen sulfide.
Indole-negative means the bacterium does not produce indole from tryptophan, which helps exclude certain genera like Proteus (which is indole-positive).
Urease-positive indicates the bacterium can hydrolyze urea to ammonia and carbon dioxide, which is a key trait to narrow down the identification to a specific genus or species.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
3m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gram-negative, Oxidase-positive Rods

Gram-negative rods are bacteria that do not retain the crystal violet stain and appear pink after Gram staining. Oxidase-positive indicates the presence of cytochrome c oxidase enzyme, which helps differentiate certain bacteria. Recognizing these traits narrows down the bacterial identification to specific genera such as Pseudomonas or certain Enterobacteriaceae.
Recommended video:
Guided course
04:46
Gram-Positive vs. Gram-Negative Cell Walls

Biochemical Tests: H₂S, Indole, and Urease

Biochemical tests detect bacterial enzyme activities: H₂S production indicates sulfur reduction; indole test detects tryptophanase enzyme; urease test identifies the ability to hydrolyze urea. The combination of positive H₂S and urease but negative indole helps differentiate closely related bacteria species.
Recommended video:
Guided course
06:59
The Ames Test

Clinical Relevance and Host Specificity

Understanding the clinical context, such as pneumonia in a sea otter, helps link bacterial identification to disease. Certain bacteria are associated with specific hosts or environments, aiding diagnosis. This ecological and pathological knowledge complements lab results for accurate identification.
Recommended video:
Guided course
01:50
Hide Within Host Cells
Related Practice
Textbook Question

Which of the following is false about scientific nomenclature?

a. Each name is specific.

b. Names vary with geographical location.

c. The names are standardized.

d. Each name consists of a genus and specific epithet.

e. It was first designed by Linnaeus.

1652
views
Textbook Question

Use the following choices to answer questions 7 and 8.

a. Animalia

b. Fungi

c. Plantae

d. Bacillota (gram-positive bacteria)

e. Pseudomonadota (gram-negative bacteria)

Into which group would you place a multicellular organism that has a mouth and lives inside the human liver?

846
views
Textbook Question

The wall-less mycoplasmas are considered to be related to gram-positive bacteria. Which of the following would provide the most compelling evidence for this?

a. They share common rRNA sequences.

b. Some gram-positive bacteria and some mycoplasmas produce catalase.

c. Both groups are prokaryotic.

d. Some gram-positive bacteria and some mycoplasmas have coccus-shaped cells.

e. Both groups contain human pathogens.

1539
views
Textbook Question

You could identify an unknown bacterium by all of the following except

a. hybridizing a DNA probe from a known bacterium with the unknown’s DNA.

b. making a fatty acid profile of the unknown.

c. specific antiserum agglutinating the unknown.

d. ribosomal RNA sequencing.

e. percentage of guanine + cytosine.

1599
views
Textbook Question

DRAW IT Use the following rRNA information to construct a cladogram for some of the organisms used in question 4. What is the purpose of a cladogram? How does your cladogram differ from a dichotomous key for these organisms?

1361
views
Textbook Question

Use the information in the following table to complete the dichotomous key to these organisms. What is the purpose of a dichotomous key? Look up each genus in Chapter 11, and provide an example of why this organism is of interest to humans.

1502
views