Bacterial Pathogenesis Quiz

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Questions and Answers

What is a characteristic of chronic bacterial infections?

They may exist without producing symptoms. (correct)

They always produce symptoms.

They are always caused by the normal flora.

The organism never reactivates.

What is the first stage of bacterial pathogenesis?

Host responses.

Colonization by growth of bacteria.

Evasion of primary host defenses.

Transmission from an external source. (correct)

Which mechanism enhances the ability of E. coli to cause disease?

Enzymatic degradation.

Capsule formation.

Pili adhesion. (correct)

Biofilm production.

During which type of transmission does a pathogen pass from mother to child?

Vertical transmission. Signup and view all the answers

What is the role of biofilm in bacterial infections?

To protect bacteria from immune defense mechanisms. Signup and view all the answers

Which of the following does NOT contribute to bacterial adherence to surfaces?

Cilia movement. Signup and view all the answers

What is the function of normal flora in the human body?

They compete with pathogenic organisms. Signup and view all the answers

Which factor is primarily responsible for the persistence of Pseudomonas in the lungs of cystic fibrosis patients?

Biofilm formation. Signup and view all the answers

What is the primary function of pathogenicity islands in bacteria?

They encode virulence factors like adhesins and exotoxins. Signup and view all the answers

Which type of toxin is an integral part of the Gram-negative bacterial cell wall?

Endotoxin Signup and view all the answers

What is a key characteristic of exotoxins?

They are secreted by both Gram-positive and Gram-negative bacteria. Signup and view all the answers

Which disease is characterized by an immune response against the M protein of Streptococcus pyogenes?

Rheumatic fever Signup and view all the answers

What term describes the period before specific symptoms of an infectious disease appear?

Incubation period Signup and view all the answers

What role do receptors on the surface of cells play in bacterial infection?

They determine the organs affected by the bacteria. Signup and view all the answers

Which statement is true regarding nonpathogenic bacterial variants?

They lack pathogenicity islands entirely. Signup and view all the answers

What is the mortality rate associated with endotoxin production?

30-50% Signup and view all the answers

What is the primary characteristic of an opportunistic organism?

It rarely causes disease in immuno-competent people. Signup and view all the answers

Which of the following best defines virulence?

The quantitative measure of pathogenicity. Signup and view all the answers

Which organism requires a lower infectious dose to cause disease based on the provided information?

Shigella Signup and view all the answers

What are the two main arms of host defenses mentioned?

Adaptive and innate immunity. Signup and view all the answers

Which mechanism of bacterial infection involves the release of polypeptides?

Exotoxin production. Signup and view all the answers

What distinguishes a pandemic from an epidemic?

A pandemic has a worldwide distribution. Signup and view all the answers

What type of infection is constantly present at a low level in a specific population?

Endemic infection Signup and view all the answers

Which of the following best describes an asymptomatic infection?

Infection detected only by the presence of antibodies. Signup and view all the answers

What role does collagenase play in bacterial pathogenesis?

It helps degrade collagen allowing bacterial spread. Signup and view all the answers

Which virulence factor prevents phagocyte adherence to bacteria?

Capsule Signup and view all the answers

What is the primary function of IgA protease in bacterial infections?

Degrades IgA to facilitate adherence to mucous membranes. Signup and view all the answers

In which type of inflammation do neutrophils predominate?

Acute pyogenic infections Signup and view all the answers

What mechanism do obligate intracellular parasites like Chlamydia use to survive within host cells?

Inhibiting fusion of the phagosome with the lysosome. Signup and view all the answers

Which of the following bacteria is known for employing pili as a virulence factor?

Escherichia coli Signup and view all the answers

What is the main function of coagulase in Staphylococcus aureus infections?

Accelerates fibrin clot formation to protect bacteria. Signup and view all the answers

What is a key function of the M protein found on Streptococcus pyogenes?

Binds IgG to avoid immune responses Signup and view all the answers

Study Notes

Pathogenesis of Bacteria

Pathogen: An organism capable of causing disease.
Opportunistic organism: Rarely causes disease in immunocompetent individuals but can cause serious infection in immunocompromised patients.
Virulence: A quantitative measure of pathogenicity. It's the number of organisms required to cause disease. A lower LD50 (lethal dose) or ID50 (infectious dose) indicates higher virulence.
Infectious dose: The number of organisms needed to cause disease. The infectious dose varies between different bacteria species. For example, Shigella requires fewer organisms than Salmonella to cause diarrhea.
Infectious diseases: Occur when microorganisms overwhelm the host defenses. This leads to the production of symptoms. The number of organisms and their virulence are critical determinants. Host defenses include innate and acquired immunity. Asymptomatic infections are common and diagnosed using antibodies against the organism in the patient's serum.
Bacterial infection mechanisms:
- Direct invasion and inflammation: Bacteria directly invade tissues and cause inflammation.
- Toxin production: Bacteria produce toxins that damage tissues.
  - Exotoxins: Polypeptides released by bacteria.
  - Endotoxins: Lipopolysaccharides part of the cell wall of Gram-negative bacteria.
- Immune-mediated mechanisms

Types of Bacterial Infections

Communicable infections: Spread from host to host (e.g., tuberculosis). Contagious infections are highly communicable.
Epidemic infections: Occur more frequently than usual.
Pandemic infections: Have a worldwide distribution.
Endemic infections: Constantly present at a low level in a specific population.
Latent infections: Result in a latent state, reactivating the growth of the organism and recurrence of symptoms.
Chronic carrier state: Organisms grow with or without producing symptoms in the host.
Normal flora: Permanent residents of the body, variations according to anatomical site.
Colonization: The presence of a new organism that's neither normal flora nor a cause of symptoms.

Stages of Bacterial Pathogenesis

Transmission: Entry from an external source.
Evasion of primary host defenses: Overcoming defenses like skin or stomach acid.
Adherence to mucous membranes: Attaching to tissues.
Colonization: Growth at the site of adherence.
Disease symptoms: Caused by toxin production or invasion/inflammation.
Host responses: Nonspecific and specific immunity.
Progression or resolution: Outcome of the infection.

Transmission

Human-to-human: Direct contact or airborne transmission.
Non-human sources: Soil, water, animals, fomites.
Vertical transmission: From mother to offspring (placenta, birth, breast milk).
Horizontal transmission: Person-to-person.
Reservoirs: Animals can be carriers of bacteria.
Vectors: Animals transmit bacteria.

Adherence to cell surfaces

Pili, capsules, glycocalyces: Structures enhancing the ability to adhere to host cells. E.coli and Neisseria gonorrhoeae use pili for adherence, while Streptococcus epidermidis and viridans streptococci strongly adhere to heart valves via glycocalyces.
Biofilm: Protective matrix formed by bacteria, composed of polysaccharides and proteins; often on prosthetic valves and IV catheters. This protects bacteria from antibodies, antibiotics, and neutrophils.

Invasion and Inflammation

Enzymes: Collagenase and hyaluronidase degrade collagen and hyaluronic acid, allowing the spread of bacteria.
Coagulase: Accelerates fibrin clot formation, thus protecting bacteria from phagocytosis. (Staphylococcus aureus)
IgA protease: Degrades IgA, allowing organisms to adhere to mucous membranes. (Neisseria gonorrhoeae, Haemophilus influenzae, and Streptococcus pneumoniae)
Leukocidin: Destroys neutrophils and macrophages.
Capsules: Prevent phagocytes from attaching to bacteria. Anti-capsular antibodies enhance phagocytosis.
Cell wall proteins: Prevent complement activation and phagocytosis (Gram-positive cocci, like Streptococcus pyogenes).

Inflammation & Intracellular Survival

Types of inflammation: Acute pyogenic (e.g., pneumonia: neutrophils predominate), Chronic granulomatous (e.g., tuberculosis: macrophages and T-cells predominate).
Intracellular survival: Essential to bacterial ability to cause disease; commonly leading to granulomatous lesions.

Intracellular Parasites

Obligate intracellular parasites: Require living host cells for reproduction (Chlamydia, Rickettsia).
Facultative intracellular parasites: Can survive either intracellularly or extracellularly (Mycobacterium, Legionella, Brucella, Listeria).
Mechanisms for intracellular survival:
- Inhibiting phagosome-lysosome fusion.
- Inhibiting phagosome acidification.
- Escaping into the cytoplasm.

Bacterial Invasion

Invasins: Proteins on bacterial surfaces that interact with host cells to invade them.
Actin microfilaments: Driving bacterial movement into host cells.
Phagosomes: Vacuoles that contain bacteria inside host cells.
Cytoplasm/adjacent cells: Bacteria can stay in vacuoles, migrate to the cytoplasm, or use tunnels to reach neighboring cells.

Different Strains of Bacteria

Genetic elements: Bacteria may belong to the same genus and species but cause different diseases. These elements, such as plasmids, transposons, genomic phages, and pathogenicity islands, encode virulence factors and are responsible for different diseases among bacterial types.

Toxin Production

Exotoxins: Secreted proteins from bacteria; highly toxic and potent. Include diphtheria toxin and cholera toxin. Toxoid is a chemically modified toxin.
Endotoxins: Components of the outer membrane of Gram-negative bacteria (lipopolysaccharides); fever, hypotension and shock are possible consequences.

Immunopathogenesis

Immune response: Symptoms of diseases like rheumatic fever and acute glomerulonephritis are due to the immune response against bacterial antigens. Antibodies cross-react with host tissues, resulting in inflammation.

Typical stages of Infectious Diseases

Incubation period: Time between acquiring the organism and symptom onset.
Prodromal period: Period with nonspecific symptoms.
Specific-illness period: Period of specific symptoms.
Recovery period: Period during which the patient becomes a chronic carrier or enters a latent state.

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Description

Test your knowledge on the characteristics and mechanisms of bacterial infections and pathogenesis. This quiz covers key concepts such as bacterial adherence, transmission, and the role of biofilms. Challenge yourself with questions on pathogenicity islands and the immune response to bacterial toxins.