Textbook Question
The following outline can be used to identify important bacteria. Fill in a representative genus in the space provided.
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Ch. 11 - The Prokaryotes: Domains Bacteria and Archaea
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398
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Table of contents
- Ch. 1 - The Microbial World and You18
- Ch. 2 - Chemical Principles20
- Ch. 3 - Observing Microorganisms Through a Microscope18
- Ch. 4 - Functional Anatomy of Prokaryotic and Eukaryotic Cells21
- Ch. 5 - Microbial Metabolism20
- Ch. 6 - Microbial Growth20
- Ch. 7 - The Control of Microbial Growth20
- Ch. 8 - Microbial Genetics19
- Ch. 9 - Biotechnology & DNA Technology20
- Ch. 10 - Classification of Microorganisms15
- Ch. 11 - The Prokaryotes: Domains Bacteria and Archaea14
- Ch. 12 - The Eukaryotes: Fungi, Algae, Protozoa, and Helminths17
- Ch. 13 - Viruses, Viroids, and Prions20
- Ch. 14 - Principles of Disease and Epidemiology21
- Ch. 15 - Microbial Mechanisms of Pathogenicity19
- Ch. 16 - Innate Immunity: Nonspecific Defenses of the Host20
- Ch. 17 - Adaptive Immunity: Specific Defenses of the Host20
- Ch. 18 - Practical Applications of Immunology20
- Ch. 19 - Disorders Associated with the Immune System19
- Ch. 20 - Antimicrobial Drugs19
- Ch. 21 - Microbial Diseases of the Skin and Eyes21
- Ch. 22 - Microbial Diseases of the Nervous System19
- Ch. 23 - Microbial Diseases of the Cardiovascular and Lymphatic Systems20
- Ch. 24 - Microbial Diseases of the Respiratory System20
- Ch. 25 - Microbial Diseases of the Digestive System20
- Ch. 26 - Microbial Diseases of the Urinary and Reproductive Systems19
- Ch. 27 - Environmental Microbiology20
- Ch. 28 - Applied and Industrial Microbiology19
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
Chapter 11, Problem 1
If you Gram-stained the bacteria that live in the human intestine, you would expect to find mostly
a. gram-positive cocci.
b. gram-negative rods.
c. gram-positive, endospore-forming rods.
d. gram-negative, nitrogen-fixing bacteria.
e. all of the above.
Verified step by step guidance1
Step 1: Understand the Gram stain and bacterial morphology terms. Gram-positive bacteria retain the crystal violet stain and appear purple, while Gram-negative bacteria do not and appear pink/red. Cocci are spherical bacteria, rods are cylindrical, and endospore-forming rods are a specific group of Gram-positive bacteria capable of forming spores.
Step 2: Recall the typical bacterial composition of the human intestine. The gut microbiota is dominated by certain groups of bacteria, primarily from the phyla Bacteroidetes and Firmicutes.
Step 3: Identify the Gram reaction and shape of the dominant intestinal bacteria. Bacteroidetes are mostly Gram-negative rods, while Firmicutes include many Gram-positive rods and cocci, but many Firmicutes in the gut are not endospore-forming.
Step 4: Evaluate the options given: (a) gram-positive cocci, (b) gram-negative rods, (c) gram-positive, endospore-forming rods, (d) gram-negative, nitrogen-fixing bacteria, and (e) all of the above. Consider which group is most abundant in the human intestine.
Step 5: Conclude that since the majority of gut bacteria are Gram-negative rods (such as Bacteroides species), the best answer corresponds to option (b).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gram Staining and Bacterial Cell Wall Structure
Gram staining differentiates bacteria based on their cell wall composition. Gram-positive bacteria have thick peptidoglycan layers that retain the crystal violet stain, appearing purple, while gram-negative bacteria have thinner peptidoglycan and an outer membrane, appearing pink after counterstaining.
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02:59
Gram-Positive Cell Walls
Common Bacterial Morphologies in the Human Intestine
The human intestine predominantly harbors gram-negative rods, such as Escherichia coli and Bacteroides species. These bacteria play key roles in digestion and maintaining gut health, contrasting with less common gram-positive cocci or endospore-forming rods in this environment.
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02:44Types of Bacterial Cell Morphology
Role of Nitrogen-Fixing Bacteria and Their Typical Habitats
Nitrogen-fixing bacteria convert atmospheric nitrogen into usable forms but are mostly found in soil or plant root nodules, not the human intestine. Thus, gram-negative nitrogen-fixing bacteria are unlikely to be predominant in the gut microbiota.
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06:18Introduction to Bacteria
Related Practice
Textbook Question
Compare and contrast each of the following:
a. Cyanobacteria and algae
b. Actinomycetes and fungi
c. Bacillus and Lactobacillus
d. Pseudomonas and Escherichia
e. Leptospira and Spirillum
f. Escherichia and Bacteroides
g. Rickettsia and Chlamydia
h. Mycobacterium and Mycoplasma
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Textbook Question
Which of the following does not belong with the others?
a. Enterobacteriales
b. Lactobacillales
c. Legionellales
d. Pasteurellales
e. Vibrionales
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Textbook Question
Draw a key to differentiate the following bacteria: cyanobacteria, Cytophaga, Desulfovibrio, Frankia, Hyphomicrobium, methanogens, myxobacteria, Nitrobacter, purple bacteria, Sphaerotilus, and Sulfolobus.
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