25 Questions
How do airborne pathogens enter the body?
Through eyes, mouth, nose, or urogenital openings, or through wounds or bites that breach the skin barrier
What is the role of a primary host in the spread of disease?
A primary host harbors the pathogen but shows no ill effects and serves as a source of infection
What is the function of polysaccharide layers made by bacterial pathogens?
To provide adhesion to host cells and resistance from phagocytosis
What is the process by which the body expels bacteria?
The expelling of bacteria from the body
What is the term for the ability of a host to fight off infection?
Host resistant
What does virulence refer to in animal systems?
The degree of damage caused by a microbe to its host.
What are virulence factors (VF)?
Molecules that assist bacteria in colonizing their host at the cellular level.
Where are the genes that code for virulence factors commonly found?
Clustered on the pathogen's chromosome or plasmid DNA, in pathogenicity islands (PI).
Why are genes for virulence factors often controlled by quorum sensing (QS)?
To ensure gene activation when the pathogen population reaches an optimal density.
What is the result of horizontal gene transfer (HGT) between bacteria?
The development of new pathogens over time.
What is the key difference between pathogenicity and virulence?
Pathogenicity is the ability of an organism to infect a host and cause disease, while virulence is the severity of the disease in infected hosts.
What is an example of an opportunistic pathogen?
An opportunistic pathogen is a microbe that normally does not cause disease but may under certain circumstances, such as when the host's immune system is compromised.
What is the term for microorganisms that colonize the body and usually do not cause disease?
Normal flora
How does the virulence of S. pneumoniae compare to that of S. typhimurium?
S. pneumoniae is more virulent than S. typhimurium, as a lower dose of S. pneumoniae can kill 100% of mice, whereas a higher dose of S. typhimurium is required to achieve the same effect.
What is an example of an ecological relationship where one species benefits and the other is not affected?
Commensalism, where one species, such as normal flora, benefits from the host without harming or helping the host.
What is the primary function of the A subunit in AB-toxins?
The A subunit enacts a mechanism on the cell, leading to decreased cell function and/or cell death.
What is the composition of the outer membrane of Gram-negative bacteria that contributes to the production of endotoxins?
Lipopolysaccharide (LPS)
What is the term for inanimate objects that can carry pathogens from an infected individual or reservoir?
Fomites
What is the necessary step for an infection to spread?
Transmission from the reservoir to the individual
What is the result of a massive release of endotoxin in a host?
Endotoxin shock
What is the purpose of adhesion in the pathogen survival process?
Adhesion allows cells to increase in number and utilize resources available at the site, leading to colonization and eventually invasion of other sites.
What is the role of enzymes in the invasion process?
Enzymes, such as collagenase, leukocidins, and hemolysins, break down host tissue and cells, allowing the pathogen to spread and causing disease.
What is the difference between bacteraemia and septicaemia?
Bacteraemia refers to the presence of bacteria in the bloodstream, while septicaemia is a systemic infection that occurs when bacteria in the bloodstream cause a severe and widespread inflammatory response.
What is the purpose of toxins in the invasion process?
Toxins penetrate and damage cells, usually to aid the producing bacterium in its invasion of host tissues.
What is septic shock, and what are its consequences?
Septic shock is a life-threatening condition that occurs when blood pressure drops to a dangerously low level after an infection, and can result in death if left untreated.
Study Notes
Virulence and Pathogenicity
- Virulence refers to the degree of damage caused by a microbe to its host.
- Pathogenicity is the ability of an organism to cause disease, determined by its virulence factors.
- Virulence factors (VF) are molecules that assist bacteria in colonizing the host at the cellular level, including physical structures (pili, flagellum) and chemical substances (toxins).
- Virulence factors are often clustered on the pathogen's chromosome or plasmid DNA, called pathogenicity islands (PI), which facilitate horizontal gene transfer and the development of new pathogens.
Virulence Factors and Quorum Sensing
- Quorum sensing (QS) is a mechanism that controls gene activation when the pathogen population reaches an optimal density.
- QS ensures that genes are triggered at the right time, avoiding alerting the host's immune system too early.
Pathogenicity vs. Virulence
- Pathogenicity is the ability of an organism to infect a host and cause disease.
- Aggressiveness is the ability of the pathogen to invade and establish itself within the host.
- Virulence is the severity of the disease in infected hosts (or degree of pathogenicity).
Ecological Relationships and Normal Flora
- Normal flora refers to microbes that colonize the body without causing disease.
- Opportunistic pathogens are microbes that normally do not cause disease but may do so under certain circumstances.
Adherence, Colonization, and Invasion
- Adherence involves bacterial attachment to host cells or tissue, resisting removal by physical means.
- Colonization is the growth of bacterial cells on the surface, utilizing available resources.
- Invasion refers to the spread of the pathogen to other locations in the host, often involving enzymes that break down host cells and tissue.
Toxins and Invasion
- Toxins can penetrate and damage cells, aiding the producing bacterium.
- Examples of toxins include tetanus toxin and V. cholera toxins.
- Endotoxins are components of the outer membrane of Gram-negative bacteria, which can cause endotoxin shock.
Transmission of Microorganisms
- Transmission from the reservoir to the individual must occur for an infection to spread.
- Transmission can occur through direct contact, indirect contact (fomites), or vectors (biological or mechanical).
- Examples of microorganisms that can be transmitted by more than one route include airborne, feco-oral, and vector-borne transmission.
This quiz covers the concept of virulence, pathogenicity, and virulence factors in microbiology, including the characteristics that contribute to virulence.
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