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Which of the following is NOT considered a mode of transmission for infections?
Which of the following is NOT considered a mode of transmission for infections?
Vertical transmission of infection can occur through all of the following routes EXCEPT:
Vertical transmission of infection can occur through all of the following routes EXCEPT:
Which of the following is a part of the innate, non-specific immune response?
Which of the following is a part of the innate, non-specific immune response?
Which of these is primarily a physical defense mechanism against infection?
Which of these is primarily a physical defense mechanism against infection?
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Lactoferrin is NOT known for its use as a:
Lactoferrin is NOT known for its use as a:
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Which immune response is characterized by a rapid and early reaction to a bacterial pathogen?
Which immune response is characterized by a rapid and early reaction to a bacterial pathogen?
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What is the primary function of the complement system in the immune response?
What is the primary function of the complement system in the immune response?
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Which of the following best describes the role of macrophages in the immune response?
Which of the following best describes the role of macrophages in the immune response?
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What is the main function of inflammation as part of the immune response?
What is the main function of inflammation as part of the immune response?
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How do microbial toxins contribute to disease?
How do microbial toxins contribute to disease?
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What is an exotoxin?
What is an exotoxin?
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Which of the following is NOT a typical sign of inflammation?
Which of the following is NOT a typical sign of inflammation?
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Which of these responses is part of the adaptive immune system?
Which of these responses is part of the adaptive immune system?
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What is the key distinction between infection and disease in the context of bacterial pathogenesis?
What is the key distinction between infection and disease in the context of bacterial pathogenesis?
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What is a primary characteristic of exotoxins regarding their production?
What is a primary characteristic of exotoxins regarding their production?
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Which of the following is a common mechanism of action for cytolytic toxins?
Which of the following is a common mechanism of action for cytolytic toxins?
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Which of the following describes a strict or primary pathogen?
Which of the following describes a strict or primary pathogen?
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What role does the 'B' component typically play in the mechanism of A-B toxins?
What role does the 'B' component typically play in the mechanism of A-B toxins?
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How does an opportunistic pathogen cause disease?
How does an opportunistic pathogen cause disease?
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What differentiates superantigens from typical antigens in terms of immune system activation?
What differentiates superantigens from typical antigens in terms of immune system activation?
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What is the most accurate definition of a commensal bacterium?
What is the most accurate definition of a commensal bacterium?
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What is the specific term for an infection transmitted from animals to humans?
What is the specific term for an infection transmitted from animals to humans?
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Where are the genes encoding many exotoxins commonly located?
Where are the genes encoding many exotoxins commonly located?
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How does the molecular weight of exotoxins typically compare to endotoxins?
How does the molecular weight of exotoxins typically compare to endotoxins?
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If a person harbors pathogenic bacteria but shows no symptoms, they are considered a:
If a person harbors pathogenic bacteria but shows no symptoms, they are considered a:
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Which statement correctly describes how bacteria can cause an infectious disease?
Which statement correctly describes how bacteria can cause an infectious disease?
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Regarding their antigenic properties, how do exotoxins compare to endotoxins?
Regarding their antigenic properties, how do exotoxins compare to endotoxins?
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What distinguishes saprophytic bacteria from other described bacteria?
What distinguishes saprophytic bacteria from other described bacteria?
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What is characteristic of pore-forming toxins (PFTs) in terms of their mechanism?
What is characteristic of pore-forming toxins (PFTs) in terms of their mechanism?
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Which scenario describes a bacterium acting as a pathogen?
Which scenario describes a bacterium acting as a pathogen?
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An immunocompromised patient is at a higher risk of disease from:
An immunocompromised patient is at a higher risk of disease from:
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Study Notes
Mechanisms of Bacterial Pathogenesis
- Bacteria cause disease through infection, which involves bacterial multiplication.
- Not all infections lead to disease.
- Infection, without disease, can be asymptomatic.
- A short-term relationship between microorganisms and the host can exist, where microbes are eliminated after infection.
- Pathogenesis involves the organism's ability to cause disease.
Microbes-Host Relationship
- Saprophytes are microbes that live in soil and on dead organic matter.
- Commensal bacteria are harmless microbes that live on the host without causing injury.
- Pathogenic bacteria can cause disease.
- Strict/Primary pathogens cause disease in healthy persons.
- Opportunistic pathogens take advantage of pre-existing conditions to cause disease.
- Examples of sites where bacteria reside include the nose, mouth/throat, stomach, gut, vagina, and skin.
Mechanisms of Bacterial Pathogenesis
- Infection is the growth and multiplication of bacteria in/on the body with or without disease.
- Disease results from tissue or organ damage due to the infection.
- Endogenous infections arise from bacteria already within the body (commensal members of normal flora moving to a different site).
- Exogenous infections arise from bacteria that are transmitted from another source/external environment.
Infection vs. Infectious Disease
- Infection is the growth and multiplication of bacteria in the body.
- Infectious disease arises from damage caused by pathogens and the immune response to the infection (immunopathogenesis).
- The immune system has mechanisms to effectively eliminate pathogens that can overwhelm it, and cause damage leading to disease.
Exogenous Infections
- Sources include patients (transmission from active disease to healthy people).
- Infected animals (zoonoses).
- Soil (saprophytic microbes).
- Carriers (individuals harboring pathogens without symptoms but transmitting the disease).
- Modes: Ingestion (food/water), Inhalation (respiratory tract), Trauma, Direct contact (skin-to-skin), Sexual transmission, Blood-borne transmission, Vector-borne transmission, Vertical (mother-to-child) transmission.
Defence Mechanisms Against Infection
- Barriers to invasion (skin, mucous membranes, stomach acid, lysozyme in tears), and physical actions like coughing, sneezing, vomiting, diarrhoea and flushing of the urinary tract prevent pathogen entry.
- Innate immune response (local response) employs phagocytes (macrophages, neutrophils, NK cells), complement system, AMPs (antimicrobial peptides), inflammatory response, and fever.
- Adaptive immune response responds to specific pathogens via antibody-mediated and cell-mediated immune responses resulting in targeted destruction of pathogens.
Soluble Defence Mediators
- Lysozyme: Breaks down bacterial peptidoglycans. (Tears, saliva, nasal secretions, lysosomal granules.)
- Lactoferrin/transferrin: Competes with microbes for iron. (Specific granules of PMNs)
- Lactoperoxidase: Inhibits many microorganisms. (Milk and saliva)
- β-Lysin: Effective against Gram-positive bacteria. (Thrombocytes, normal serum.)
- Chemotactic factors: Promote migration of phagocytic cells. (Complement and chemokines)
- Properdin: Activates complement in absence of antibody. (Plasma)
- Lectins: Promote microbial phagocytosis. (Plasma)
- Cationic peptides: Disrupt microbial membranes, block cell transport. (Polymorphonuclear granules, epithelial cells)
Lactoferrin
- Host cells secrete lactoferrin that bind iron and compete with microorganisms, preventing pathogen acquisition of iron and aiding in sequestration.
- Pathogens can respond by "stealing" iron or producing stealth siderophores that are resistant to neutralization measures.
Mother-to-Child Transmission
- Infection can be transmitted across the placenta, during delivery, or through breastfeeding.
- Different bacteria and viruses can be transmitted through these methods to cause disease.
Pathogenic Infection
- Microbes cause disease by killing host cells directly or by releasing toxins.
- Exposure, adhesion, invasion, colonization, toxins, tissue damage lead to disease state.
Microbial Toxins
- Exotoxins are secreted proteins that may cause characteristic diseases (diphtheria, tetanus, cholera).
- Examples of Exotoxins classes are cytolytic, A-B toxins, and superantigens.
- Endotoxins are components of outer bacterial layers, released from dying cells of gram-negative bacteria and is a potent activator of inflammatory reactions (ex. LPS).
Exotoxins (Specific Types)
- Pore-forming toxins (PFTs). Water-soluble molecules causing oligomerization and generating pores in the host cell membrane leading to cell death.
- Membrane-disrupting enzymes. Proteins that degrade sphingomyelin and phospholipids of the cell membrane leading to cell death.
- A-B toxins. Have a binding subunit (B) and an active subunit (A) which cause disease through different mechanisms (e.g., cholera toxin).
- Superantigens. Trigger excessive and ineffective activation of T-cells and release of cytokines, leading to toxic shock syndrome.
Endotoxins
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Part of outer cell wall of Gram-negative bacteria and released when the bacterial cell wall breaks.
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Examples are Lipid A and O antigens.
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At low concentrations, stimulate protective responses (e.g., increases in cytokines, antibody synthesis, inflammatory response).
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At high concentrations, cause shock and death through disseminated intravascular coagulation, hypotension and hypoglycemia.
Phagocytes and Inflammation
- Macrophages use surface receptors, initiate phagocytosis, leading to lysis, release of cytokines and the induction of leukocyte infiltration (inflammation) into affected sites.
Inflammation
- Localized physical condition involving redness, swelling, heat, pain, in response to injury or infection.
- Is a defense mechanism, where the immune system recognizes damaged cells, irritants, and pathogens to begin the healing process.
- The four cardinal signs are: redness, heat, pain, swelling.
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Description
Test your knowledge on modes of infection transmission and key concepts of the immune response. This quiz covers various aspects including innate and adaptive immunity, inflammation, and the role of different immune cells in fighting infections. Perfect for students of immunology and microbiology!
