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Questions and Answers
Which pathogen is associated with producing Type IV pili for attachment?
Which pathogen is associated with producing Type IV pili for attachment?
What role do bacterial capsules predominantly play in terms of pathogen survival?
What role do bacterial capsules predominantly play in terms of pathogen survival?
Which component of some Streptococcus species aids in immune evasion?
Which component of some Streptococcus species aids in immune evasion?
What is the function of Type 1 fimbriae produced by Enterotoxigenic E. coli (ETEC)?
What is the function of Type 1 fimbriae produced by Enterotoxigenic E. coli (ETEC)?
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Which pathogen is known to cause cholera and is associated with methylphenylalanine?
Which pathogen is known to cause cholera and is associated with methylphenylalanine?
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What happens to pH levels when cariogenic bacteria proliferate due to carbohydrate fermentation?
What happens to pH levels when cariogenic bacteria proliferate due to carbohydrate fermentation?
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How does the Herpes simplex virus evade the immune system?
How does the Herpes simplex virus evade the immune system?
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Which of the following is NOT a main virulence factor of Candida Albicans?
Which of the following is NOT a main virulence factor of Candida Albicans?
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What role do cytotoxic T cells play in the interaction between pathogens and the host?
What role do cytotoxic T cells play in the interaction between pathogens and the host?
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Why are pathogens considered successful when they do not kill their host?
Why are pathogens considered successful when they do not kill their host?
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What role do adhesins play in bacterial infection?
What role do adhesins play in bacterial infection?
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Which type of pili is known for its ability to facilitate 'twitching' motility?
Which type of pili is known for its ability to facilitate 'twitching' motility?
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What is one consequence of a bacterium utilizing its adhesins effectively?
What is one consequence of a bacterium utilizing its adhesins effectively?
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Which of the following is NOT a known mechanism of virulence factors?
Which of the following is NOT a known mechanism of virulence factors?
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Streptococcus mutans is associated with which disease and adhesin?
Streptococcus mutans is associated with which disease and adhesin?
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What best defines a primary pathogen?
What best defines a primary pathogen?
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How do exoenzymes contribute to bacterial virulence?
How do exoenzymes contribute to bacterial virulence?
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What is the primary mechanism of action for endotoxins?
What is the primary mechanism of action for endotoxins?
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Which term refers to the degree or intensity of pathogenicity of a microorganism?
Which term refers to the degree or intensity of pathogenicity of a microorganism?
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Which bacterial pathogen uses Type 1 fimbriae to cause Traveler's diarrhea?
Which bacterial pathogen uses Type 1 fimbriae to cause Traveler's diarrhea?
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What are virulence factors primarily responsible for?
What are virulence factors primarily responsible for?
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Which type of pathogen is part of the normal microbiota but can cause disease under certain conditions?
Which type of pathogen is part of the normal microbiota but can cause disease under certain conditions?
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What is required for a pathogen to survive in a host?
What is required for a pathogen to survive in a host?
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What does pathogenicity refer to?
What does pathogenicity refer to?
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Which of the following is NOT a characteristic of virulence factors?
Which of the following is NOT a characteristic of virulence factors?
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Which of the following components contribute to the chain of infection?
Which of the following components contribute to the chain of infection?
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What condition is characterized by the presence of pus-forming bacteria in the blood?
What condition is characterized by the presence of pus-forming bacteria in the blood?
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Which virulence factor allows Staphylococcus aureus to evade phagocytosis?
Which virulence factor allows Staphylococcus aureus to evade phagocytosis?
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What are the minor changes in viral proteins resulting from point mutations called?
What are the minor changes in viral proteins resulting from point mutations called?
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Which of the following is a virulence factor associated with Streptococcus mutans?
Which of the following is a virulence factor associated with Streptococcus mutans?
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What is the primary function of leukocidins produced by certain pathogens?
What is the primary function of leukocidins produced by certain pathogens?
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What mechanism allows some enveloped viruses to avoid the host's immune system?
What mechanism allows some enveloped viruses to avoid the host's immune system?
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What type of variation occurs through gene re-assortment resulting in significant protein changes in viruses?
What type of variation occurs through gene re-assortment resulting in significant protein changes in viruses?
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What role do fimbriae play for Porphyromonas gingivalis in oral health?
What role do fimbriae play for Porphyromonas gingivalis in oral health?
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Study Notes
Pathogens and Disease
- A pathogen is any microorganism that can cause disease in a host organism.
- Primary pathogens can cause disease in healthy individuals.
- Opportunistic pathogens are part of the normal microbiota and only cause disease in immunocompromised hosts.
- Pathogenicity refers to the ability of a pathogen to cause disease.
- Virulence is the degree or intensity of pathogenicity.
- Virulence factors are mechanisms that determine the degree to which a pathogen causes damage, invasion, and infectivity.
Chain of Infection
- The chain of infection is a model that describes the process of infection.
- Virulence factors are a key element of the chain of infection.
How Pathogens Survive
- To survive, pathogens need a suitable environment, a source of nutrients, and protection from harmful elements.
Mechanisms of Virulence Factors
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Adhesion: Pathogens use various mechanisms to adhere to and colonize host cells. These mechanisms include:
- Pili: Hair-like structures that allow bacteria to attach to host cells using a ‘twitching’ motility.
- Fimbriae: Similar to pili but shorter and more numerous — they can be involved in attachment.
- Capsules: A protective layer that surrounds some bacteria, helping them evade phagocytosis and promote adhesion.
- Adhesins: Protein or glycoprotein molecules on the bacterial cell wall that bind to specific receptors on host cells.
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Evasion of Phagocytosis: Defense mechanisms used by pathogens to avoid being engulfed and destroyed by phagocytes:
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Antiphagocytic factors: These factors prevent phagocytosis. For example:
- M protein: Found in the fimbriae of some Streptococcus species, it alters the bacterial surface.
- Mycolic acid: A waxy substance in the cell wall of Mycobacterium tuberculosis.
- Coagulase: An exoenzyme produced by Staphylococcus aureus that triggers the fibrinogen-to-fibrin cascade, coating bacteria in fibrin clots and preventing phagocytosis.
- Kinases: Exoenzymes that digest fibrin clots, allowing pathogens to escape and spread.
- Antigenic variation: Pathogens change their surface proteins to avoid recognition by the host's immune system.
- Leukocidins: Toxins that destroy phagocytes.
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Antiphagocytic factors: These factors prevent phagocytosis. For example:
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Immunoevasion: Mechanisms to evade the host's immune system:
- Destruction of T lymphocytes: Some pathogens target and destroy T lymphocytes.
- Intracellular position: Some pathogens reside inside host cells, where they are protected from the immune system.
- Immunosuppression: Directly suppressing the immune system.
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Toxigenicity:
- Exotoxins: Protein toxins secreted by bacteria.
- Endotoxins: Lipopolysaccharide (LPS) components of the outer membrane of Gram-negative bacteria.
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Enzymatic: Pathogens produce exoenzymes that damage host tissues:
- Exoenzymes: Enzymes secreted by bacteria that break down host cell components.
Terminology Describing Pathogens in the Bloodstream
- Bacteraemia: Presence of bacteria in the blood.
- Pyaemia: Presence of pus-forming bacteria in the blood.
- Toxaemia: Presence of toxins in the blood.
- Septicaemia: Multiplying bacteria in the blood.
Viral Virulence
- Adhesins: Viral adhesins, often found on the viral capsid or envelope, bind to specific cell receptors (tropism).
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Antigenic variation:
- Antigenic drift: Result of point mutations that cause minor changes in spike proteins, leading to new strains.
- Antigenic shift: The gene re-assortment between different viral strains, leading to significant changes in spike proteins, potentially causing a pandemic.
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Examples:
- Influenza virus: Spike protein hemagglutinin.
- HIV: Glycoprotein g20 .
Virulence Factors in Oral Health
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Porphyromonas gingivalis:
- Fimbriae: Modify and stimulate immune responses in the periodontium.
- Gingipains: Proteases (exoenzymes) that break down structural proteins of the periodontium.
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Streptococcus mutans:
- Adhesion, acidogenicity, and acid tolerance: These combined factors contribute to dental caries by promoting a shift in the ecology of dental plaque.
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Herpes simplex virus:
- Latency and reactivation: Hides from the immune system in neurons and non-neuronal cells, emerging when immune resistance is low.
- Clinical presentation: Herpes labialis (cold sore).
- Candida albicans:
- Opportunistic fungal infection: A common cause of opportunistic fungal infections in humans.
Virulence Factors of Candida albicans
- Exoenzymes: Secreted aspartyl proteases (Sap proteins).
- Adhesions: Enable attachment to host cells.
- Pleomorphism: Ability to adapt to different environmental conditions.
Conclusion
- Pathogens have and continue to evolve complex strategies using virulence factors to increase their chances of survival and avoid the host's immune system.
- The continuous interplay between pathogens and host cells is dynamic.
- The emergence of new virulence factors in pathogens is a constant threat that requires ongoing study and research.
- The most successful pathogens are those that exploit the host without causing immediate death, ensuring their long-term survival.
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Pathogens
