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Chapter 22: Problem 77

More than 100 bacterial species live on the surface of the human body. Bacteria cover portions of human skin in concentrations of up to 8 million cells per square centimeter. In particular, human sebaceous glands support the growth of the bacterium Propionibacterium acnes, which uses oil from the glands for food. Two strains of P. acnes are associated with the development of acne on human skin, but other strains are associated with healthy skin. Which statement best describes the relationship between humans and P. acnes? a. In some cases it is commensal and in others it is parasitic. b. In some cases it is mutualistic and in others it is commensalistic. c. It is almost always parasitic. d. It is almost always mutualistic.

Short Answer

Expert verified
a. In some cases it is commensal and in others it is parasitic.

Step by step solution

01

Understanding the Relationship

Given the information, P. acnes can be beneficial or harmful. It helps maintain healthy skin for some strains but can contribute to acne development in other strains.
02

Identify the Types of Symbiotic Relationships

1. Mutualistic: Both organisms benefit. 2. Commensalistic: One organism benefits, the other is unaffected. 3. Parasitic: One organism benefits, and the other is harmed.
03

Classify Each Relationship

Healthy skin strains - If P. acnes helps humans by keeping skin healthy, the relationship is either mutualistic or commensalistic. Acne-associated strains - If P. acnes causes harm by leading to acne, the relationship is parasitic.
04

Evaluate Each Choice

a. Commensal in some cases (healthy skin) and parasitic in others (acne). b. Mutualistic (beneficial interaction) in some cases and commensalistic in others. c. Always harmful: not correct, because some strains help maintain healthy skin. d. Always beneficial: not correct, because some strains cause acne.
05

Conclusion

Answer choice a is the best fit. P. acnes can be commensal (harmless) or parasitic (harmful), depending on the strain.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

mutualistic relationship
A mutualistic relationship is when both organisms involved benefit from the association. One classic example in microbiology is the relationship between humans and gut bacteria.

These bacteria help digest food and synthesize vital nutrients like vitamin K and B vitamins.
In return, they get a warm, nutrient-rich environment to live in. This win-win relationship showcases how mutualism supports both organisms.

There is a balance that allows both to thrive. Similarly, certain strains of bacteria can benefit human skin by occupying space and resources, thereby preventing harmful pathogens from colonizing.
commensalism in bacteria
Commensalism is a type of symbiotic relationship where one organism benefits while the other is neither helped nor harmed. In the context of bacteria, many live on human skin without causing any issues.

Take Propionibacterium acnes, for example. Certain strains of this bacterium use oils from our sebaceous glands as food. This doesn't harm us and doesn't provide us with a direct benefit, either.
Thus, we could say that these strains have a commensal relationship with humans.

Commensal bacteria are important because they can help maintain the balance of microbial communities on our skin.
parasitism in microbiology
Parasitism is a relationship where one organism benefits at the expense of the other. This relationship can cause harm or disease in the host organism.

In microbiology, parasitic bacteria can lead to infections and illnesses. An example is the relationship between certain strains of Propionibacterium acnes and humans:
while some strains are harmless or even beneficial, others can contribute to acne by clogging hair follicles and leading to inflammation.

This results in various forms of acne, causing discomfort and sometimes secondary infections.
This relationship highlights the importance of understanding how different bacterial strains interact with their hosts.

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Most popular questions from this chapter

In a hypothetical research situation, scientists discover bacterial endospores in silt at the bottom of a marsh that has been contaminated with a pollutant for 25 years. The silt of the marsh was deposited in annual layers. The age of the endospores can be estimated, then, by identifying the layer of silt in which the endospores are found. In flask A, researchers place 20-year-old endospores along with growth medium and the pollutant. In flask B, researchers place 100-year-old endospores along with growth medium and the pollutant. Which statement describes the results you would expect to see in the growth of the flasks? a. The growth in flask A will exceed that of flask B. b. The growth in flask B will exceed that of flask A. c. The growth each flask will be about equal. d. There will be little to no growth in each flask.

Describe briefly how you would detect the presence of a non culturable prokaryote in an environmental sample. a. Recombinant DNA techniques are used to detect the presence of a non- culturable prokaryote in an environmental sample. Polymerase chain reaction is used to amplify selected portions of prokaryotic DNA. b. Molecular biology techniques are used to detect the presence of a non- culturable prokaryote in an environmental sample. Electrophoresis is used to amplify selected portions of prokaryotic DNA. c. Molecular biology techniques are used to detect the presence of a non- culturable prokaryote in an environmental sample. Polymerase chain reaction is used to amplify selected portions of prokaryotic DNA. d. Recombinant DNA techniques are used to detect the presence of a non- culturable prokaryote in an environmental sample. Electrophoresis is used to amplify selected portions of prokaryotic DNA.

Explain the statement that both Archaea and Bacteria have the same basic structures, but these structures are built from different chemical components. a. Typical cells in Archaea and Bacteria contain a cell wall, cell membrane, nucleoid region, ribosomes, and often a capsule, flagellum, and pili. However, these are sometimes made from different chemical compounds. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Plasma membrane lipids of Bacteria are fatty acids while those of Archaea are phytanyl groups. b. Typical cells in Archaea and Bacteria contain a cell wall, cell membrane, nucleoid region and often a capsule, flagellum, and pili but in some instances different chemical compounds make them. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Bacteria contain 70S ribosomes while Archaea contain 80S ribosomes. c. Typical cells in Archaea and Bacteria contain a cell wall, nuclear membranes, nucleoid region and often a capsule, flagellum, and pili but in some instances different chemical compounds make them. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Plasma membrane lipids of bacteria are fatty acids, while the plasma membrane lipids of Archaea are phytanyl groups. d. Typical cells in Archaea and Bacteria contain a cell wall, cell membrane, nucleoid region and often a capsule, flagellum, and pili but in some instances different chemical compounds make them. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Plasma membrane lipids of Bacteria are phytanyl groups, while the plasma membrane lipids of Archaea are fatty acids.

In a hypothetical research situation, scientists discover bacterial endospores in silt at the bottom of a marsh that has been contaminated with a pollutant for 25 years. The silt of the marsh was deposited in annual layers. The age of the endospores can be estimated, then, by identifying the layer of silt in which the endospores are found. In flask A, researchers place 20-year-old endospores along with growth medium and the pollutant. In flask B, researchers place 100-year-old endospores along with growth medium and the pollutant. Suppose the researchers observe the flasks for a while, continuing to replenish growth medium and pollutant as necessary. Which statement describes the results you would expect to see in the growth of the flasks after some time? a. The growth in flask A will continue to exceed that of flask \(\mathrm{B}\) . b. The growth in flask \(\mathrm{B}\) will exceed continue to exceed that of flask A. c. Eventually, the difference in the growth in each d. Eventually, will be little to no growth in each flask.

Have foodborne illnesses related to biofilms changed over time? Explain.. a. Yes, better sterilization and canning procedures have reduced the incidence of botulism. Most cases of foodborne illness now are related to small-scale food production. b. No, better sterilization and canning procedures have reduced the incidence of botulism. Most cases of foodborne illness now are related to small-scale food production.. c. No, better sterilization and canning procedures have increased the incidence of botulism. Most cases of foodborne illnesses now are related to large-scale food production. d. Yes, better sterilization and canning procedures have reduced the incidence of botulism. Most cases of foodborne illnesses now are related to large-scale food production.
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