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Ch. 11 - The Prokaryotes: Domains Bacteria and Archaea
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
All textbooksTortora 14th EditionCh. 11 - The Prokaryotes: Domains Bacteria and ArchaeaProblem 6
Chapter 11, Problem 6

Which one of the following does not belong with the others?
a. Enterococcus
b. Lactobacillus
c. Staphylococcus
d. Streptococcus
e. All are grouped together.

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1
Step 1: Identify the characteristics of each genus listed: Enterococcus, Lactobacillus, Staphylococcus, and Streptococcus.
Step 2: Note that Enterococcus, Lactobacillus, and Streptococcus are all Gram-positive cocci or rods that are generally catalase-negative and often associated with lactic acid production.
Step 3: Recognize that Staphylococcus is also Gram-positive but differs because it is catalase-positive and forms clusters rather than chains or pairs.
Step 4: Compare the oxygen requirements and typical habitats of these genera; for example, Lactobacillus is a rod-shaped lactic acid bacterium, while the others are cocci.
Step 5: Conclude which genus does not belong based on differences in morphology, catalase reaction, or grouping characteristics.

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Key Concepts

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

Gram-Positive Bacteria Classification

Gram-positive bacteria have thick peptidoglycan cell walls and stain purple in Gram staining. Understanding their classification helps differentiate genera like Enterococcus, Lactobacillus, Staphylococcus, and Streptococcus based on shape, arrangement, and physiology.
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Bacterial Morphology and Arrangement

Bacterial shape and arrangement are key for identification: cocci are spherical, bacilli are rod-shaped. Staphylococcus and Streptococcus are cocci but differ in cluster (grape-like) versus chain arrangements, while Lactobacillus is rod-shaped, distinguishing it from the others.
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Oxygen Requirements and Metabolism

Different genera vary in oxygen tolerance: Staphylococcus is facultative anaerobic, Enterococcus is also facultative anaerobic, Lactobacillus is aerotolerant anaerobic, and Streptococcus is facultative anaerobic. These metabolic traits help group or separate bacteria in clinical and ecological contexts.
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Related Practice
Textbook Question

Which of the following pairs is mismatched?

a. Anaerobic endospore-forming gram-positive rods—Clostridium

b. Facultatively anaerobic gram-negative rods—Escherichia

c. Facultatively anaerobic gram-negative rods—Shigella

d. Pleomorphic gram-positive rods—Corynebacterium

e. Spirochete—Helicobacter

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Textbook Question

When Legionella was newly discovered, why was it classified with the pseudomonads?

a. It is a pathogen.

b. It is an aerobic gram-negative rod.

c. It is difficult to culture.

d. It is found in water.

e. None of the above

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Textbook Question

These organisms are important in sewage treatment and can produce a fuel used for home heating and for generating electricity.

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Textbook Question

Which of the following terms is the most specific?

a. bacillus

b. Bacillus

c. gram-positive

d. endospore-forming rods and cocci

e. anaerobic

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Textbook Question

Which of the following is an intracellular parasite?

a. Rickettsia

b. Mycobacterium

c. Bacillus

d. Staphylococcus

e. Streptococcus

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Textbook Question

Spirillum is not classified as a spirochete because spirochetes

a. do not cause disease.

b. possess axial filaments.

c. possess flagella.

d. are prokaryotes.

e. none of the above

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