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What role do adhesins play in bacterial colonization?
What role do adhesins play in bacterial colonization?
Which of the following statements about invasins is correct?
Which of the following statements about invasins is correct?
Which mechanism of pathogenic damage involves the production of toxins?
Which mechanism of pathogenic damage involves the production of toxins?
What distinguishes exotoxins from endotoxins?
What distinguishes exotoxins from endotoxins?
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What is one of the effects of super antigens produced by certain exotoxins?
What is one of the effects of super antigens produced by certain exotoxins?
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What term is used for the genetic traits that enable bacteria to cause damage to a human host?
What term is used for the genetic traits that enable bacteria to cause damage to a human host?
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Which of the following processes allows bacteria to damage host tissue directly?
Which of the following processes allows bacteria to damage host tissue directly?
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What is the correct sequence of events for a pathogen to cause disease?
What is the correct sequence of events for a pathogen to cause disease?
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What is the first step for a pathogen in the infection cycle?
What is the first step for a pathogen in the infection cycle?
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What factor is crucial for determining the severity of infection caused by bacteria?
What factor is crucial for determining the severity of infection caused by bacteria?
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Which aspect of the bacterial genome is essential for its ability to invade hosts?
Which aspect of the bacterial genome is essential for its ability to invade hosts?
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How do bacteria typically evade host defense mechanisms?
How do bacteria typically evade host defense mechanisms?
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What are the symptoms of a bacterial infection primarily produced by?
What are the symptoms of a bacterial infection primarily produced by?
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How does the capsule of a bacterium help it evade host defenses?
How does the capsule of a bacterium help it evade host defenses?
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What is the role of mucus and epithelial cells in the infection process?
What is the role of mucus and epithelial cells in the infection process?
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What is an example of a mechanism by which microbes make themselves invisible to the immune system?
What is an example of a mechanism by which microbes make themselves invisible to the immune system?
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Which of the following is NOT considered a bacterial virulence mechanism?
Which of the following is NOT considered a bacterial virulence mechanism?
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Which bacterial characteristic directly contributes to its ability to invade the host?
Which bacterial characteristic directly contributes to its ability to invade the host?
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Which type of toxin is produced only by Gram-negative bacteria?
Which type of toxin is produced only by Gram-negative bacteria?
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What is the primary characteristic of invasiveness in bacteria?
What is the primary characteristic of invasiveness in bacteria?
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What distinguishes exotoxins from endotoxins regarding heat stability?
What distinguishes exotoxins from endotoxins regarding heat stability?
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Which of the following best describes the term 'toxigenesis' in bacterial pathogenicity?
Which of the following best describes the term 'toxigenesis' in bacterial pathogenicity?
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What role do degradative enzymes play in bacterial pathogenesis?
What role do degradative enzymes play in bacterial pathogenesis?
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What is a major effect of superantigens on the immune system?
What is a major effect of superantigens on the immune system?
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Which of the following is true regarding the specificity of exotoxins?
Which of the following is true regarding the specificity of exotoxins?
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How do super-antigens function in immunopathogenesis?
How do super-antigens function in immunopathogenesis?
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Which of the following is NOT a type of exotoxin?
Which of the following is NOT a type of exotoxin?
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What is the outcome of bacterial colonization and growth within a host?
What is the outcome of bacterial colonization and growth within a host?
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What is an example of a symptom caused by endotoxins?
What is an example of a symptom caused by endotoxins?
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What is meant by the term 'virulence' in the context of bacterial pathogenesis?
What is meant by the term 'virulence' in the context of bacterial pathogenesis?
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What type of toxins can be converted into toxoids?
What type of toxins can be converted into toxoids?
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Which of the following is NOT considered a step in bacterial virulence?
Which of the following is NOT considered a step in bacterial virulence?
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Which organism is typically associated with endotoxin production?
Which organism is typically associated with endotoxin production?
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Study Notes
Bacterial Pathogenesis
- Bacterial pathogenesis is the process through which bacteria cause disease.
- The degree to which disease is caused is called virulence.
- Virulence factors are genetic traits that cause damage to the host.
- Bacteria cause disease by byproducts like gas and acids leading to direct tissue damage.
- Bacteria can also cause disease by releasing toxins into the bloodstream.
- These toxins travel to various organs causing harm.
- Virulence includes invasiveness and toxigenicity.
Bacterial Virulence Factors
- These are elements that are essential for invasion, dissemination, and pathogenicity.
- Examples include:
- Virulent surface proteins
- Iron-binding proteins
- Exotoxins
- Virulence plasmids
- Toxin-producing phages
- Capsules
- Adhesins
- Lipopolysaccharides (LPS)
- Flagella
Introduction
- Bacteria have the ability to invade, adhere, and colonize environments.
- Bacteria can gain access to food in order to survive.
- Bacteria can evade the host's immune system.
- Bacteria create a niche or colony for themselves.
- Byproducts of growth (acids, gases) can lead to damage and harm to the host.
Mechanisms of Bacterial Pathogenicity
-
Invasiveness: The ability to invade tissues.
- Colonization - adherence and initial multiplication.
- Production of substances to facilitate invasion.
- Ability to evade or bypass host defence mechanisms.
- Toxigenesis: The ability to produce toxins.
Colonization, Adhesion, and Invasion
- Colonization is the establishment of the pathogen.
- The pathogen starts at an appropriate point of entry and establishes a colony.
- Colonization depends on environmental conditions.
- Some pathogens do not spread efficiently at higher temperatures.
Adherence
- Bacteria have adhesins that bind to specific receptors.
- These receptors keep the bacteria from being washed away.
- Glycocalyx and fimbriae(attachment pili) are involved in adherence.
Microbial Adhesions
- Most microbial adhesions are glycoproteins or lipoproteins located on the glycocalyx.
- They can also be found on capsules, capsids, pili, fimbriae or flagella.
Invasion
- Bacterial invasion is aided by the production of extracellular substances called invasins.
- Invasins are mostly proteins and enzymes that either destroy barriers or penetrate cells.
- Damage to the host by this process becomes the underlying pathology of a disease.
Pathogenic Actions of Bacteria
- Bacteria cause damage through 3 general mechanisms:
- Direct damage or tissue destruction
- Toxin-induced damage
- Hypersensitivity reactions
Toxin-Induced Damage
- Toxins are bacterial products that directly harm tissues or initiate destructive biological processes.
- Toxins can cause cell lysis.
- Toxins can be categorised as exotoxins or endotoxins.
Toxins: Exotoxin and Endotoxin Classifications
- Exotoxins are produced by both Gram-positive and Gram-negative bacteria.
- Proteins that are often released from cells.
- Many different types based on structure and function.
- Heat-liable and can be converted to toxoids.
- Bind to specific receptors on host target cells.
- Endotoxins are produced only by Gram-negative bacteria.
- Part of the cell wall (lipids A).
- Only one type.
- Heat-stable
- Affects diverse range of host cells and systems.
- Toxoids cannot be made.
Endotoxins
- Released when bacteria are killed by phagocytosis or antibiotics.
- NOT tissue or organ-specific, they cause general damage (fever, hypotension, weakness) to the host.
Endotoxin-Mediated Toxicity
- Symptoms include fever, leukopenia followed by leukocytosis, complement activation, thrombocytopenia, disseminated intravascular coagulation, reduced peripheral circulation, shock, and death.
Exotoxins
- 5 types, and each type is target-specific. Examples are:
- Enterotoxins
- Neurotoxins
- Cytotoxins
- Hematologic toxins
- Super antigens
Super Antigens
- Substances that hyper-stimulate lymphocytes and induce an immune response that is thousands of times stronger than normal.
- Result in a rapid increase in vasodilation and decrease in blood pressure, leading to shock.
Host Factors
- Host Factors play important roles in bacterial pathogenesis, including congenital defects and immunodeficiency
- Other diseases related to various conditions increase a person's susceptibility to infection.
Immunopathogenesis
- The host's immune response is the primary cause of disease symptoms in patients with bacterial infections.
- Symptoms are usually due to innate, immune, and inflammatory responses triggered by the infection.
Mechanisms for Escaping Host Defenses
- Bacteria attempt to avoid the immune system's clearance of them.
- Examples include encapsulation, antigenic mimicry, masking using external components mimicking host cells.
- These methods make the microbe less visible to the host immune system and/or resist enzymes.
Summary: Bacterial Virulence Mechanisms
- Adherence (Colonization)
- Invasion
- Degradative enzymes
- Exotoxins
- Endotoxin
- Evasion of phagocytic & immune clearance
- By products of growth (gas, acid)
- Super antigens
- Escaping host defenses
References
- Medical Microbiology by Murray, Rosenthal Pfeiffer
- 7th Edition, Chapter 14
- Images from both Murray and Google.
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Description
Test your knowledge about the mechanisms of bacterial colonization, the roles of adhesins and invasins, and the differences between exotoxins and endotoxins. This quiz covers the pathogenic damage mechanisms and the genetic traits that enable bacteria to cause human disease, providing a comprehensive overview of bacterial virulence.
