Microbiology Pathogenicity Overview

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Questions and Answers

What is a characteristic of lysogeny in bacteria?

Bacteriophages can only infect gram-positive bacteria.

Bacteriophages can cause lysis of all bacterial cells.

Bacteriophages integrate their DNA into the bacterial genome. (correct)

Bacteriophages replicate independently of the host's DNA.

What causes symptoms in fungal diseases?

Destruction of red blood cells.

Massive immune response to viruses.

Direct infection of the bloodstream.

Production of toxins, allergic reactions, or tissue invasion. (correct)

Which of the following best defines a portal of exit?

The mechanism by which a pathogen is engulfed by immune cells.

The initial site of pathogen entry into the body.

The site through which a pathogen exits the host to infect another individual. (correct)

The location where antibiotics are administered.

How do helminthic diseases primarily cause health issues?

Through the presence of large parasitic worms causing blockage or nutrient loss. Signup and view all the answers

What is a major characteristic of protozoan diseases?

They result in the destruction of host tissues or immune responses. Signup and view all the answers

Which of the following is the most common portal of entry for pathogens?

Mucous membranes Signup and view all the answers

What does ID50 represent in the context of infectious diseases?

The number of pathogens needed to infect 50% of a population Signup and view all the answers

Which structure is NOT used by microbes for adhesion to host cells?

Flagella Signup and view all the answers

How do capsules contribute to the pathogenicity of bacteria?

By preventing phagocytosis by immune cells Signup and view all the answers

What is the significance of a low LD50 in a pathogen?

It indicates a higher virulence requiring fewer infectious particles to cause death Signup and view all the answers

Which of the following is an example of a pathogen entering through the gastrointestinal tract?

Salmonella Signup and view all the answers

What role do fimbriae play in bacterial infection?

They help bacteria adhere to host cell receptors Signup and view all the answers

Which of the following is NOT a method of pathogen entry into the body?

Lymphatic system Signup and view all the answers

What is the primary function of peptidoglycan in bacterial cell walls?

To contribute to pathogenicity Signup and view all the answers

Which enzyme is produced by Staphylococcus aureus to avoid phagocytosis?

Coagulase Signup and view all the answers

What is antigenic variation?

Alteration of surface proteins to evade immune response Signup and view all the answers

How do bacteria typically use the host's cytoskeleton for entry into cells?

By manipulating host receptors for endocytosis Signup and view all the answers

Which mechanism do bacteria use to prevent destruction by phagocytosis?

Having capsules that impede phagocyte adherence Signup and view all the answers

What role do siderophores play in bacterial infection?

They bind iron to facilitate nutrient acquisition Signup and view all the answers

How do exotoxins primarily damage host cells?

By inhibiting protein synthesis Signup and view all the answers

What distinguishes endotoxins from exotoxins?

Endotoxins are components of Gram-negative bacteria's outer membrane Signup and view all the answers

Which type of toxin stimulates excessive immune responses?

Superantigens Signup and view all the answers

What is the purpose of the Limulus Amebocyte Lysate (LAL) assay?

To detect endotoxins in pharmaceuticals Signup and view all the answers

What defines the function of plasmids in bacterial pathogenicity?

Plasmids can carry genes for antibiotic resistance and toxins Signup and view all the answers

Which of the following is a consequence of microbial direct damage?

Destruction of host tissues through enzyme secretion Signup and view all the answers

How do leukocidins function in the context of bacterial pathogenicity?

They kill white blood cells, including phagocytes Signup and view all the answers

Study Notes

Pathogenicity Overview

Pathogens enter the body through specific portals, including mucous membranes (respiratory, gastrointestinal, genitourinary, conjunctiva) and skin (cuts, abrasions, hair follicles).
The parenteral route involves direct entry into tissues via punctures, injections, or bites.

Virulence Factors

ID50 (Infectious Dose 50): The number of pathogens needed to infect 50% of a population.
LD50 (Lethal Dose 50): The number of pathogens needed to kill 50% of a population.
Lower ID50/LD50 values indicate higher virulence.

Adherence Mechanisms

Microbes adhere to host cells using adhesins, glycocalyx (e.g., capsules), fimbriae, and pili.
- Adhesins are bacterial surface proteins that bind to host cell receptors.
- Glycocalyx enhances adherence to surfaces, forming biofilms.
- Fimbriae and pili are hair-like appendages enabling adherence.

Evasion of the Immune System

Capsules: Polysaccharide or protein layers that prevent phagocytosis.
Cell wall components:
- Peptidoglycan can contribute to pathogenicity.
- Mycolic acid in Mycobacteria prevents digestion within phagocytes.
- Lipopolysaccharide (LPS) in Gram-negative bacteria triggers inflammatory responses.
Coagulases: Cause blood clotting, hindering immune detection.
Kinases: Break down fibrin, allowing bacterial spread.
Hyaluronidase: Breaks down connective tissue, aiding spread.
Collagenase: Breaks down collagen in connective tissue, aiding spread.

Antigenic Variation

Pathogens alter their surface proteins to evade the host immune response (e.g., Influenza virus).

Internalization Mechanisms

Some bacteria use the host cell's cytoskeleton (actin filaments) to enter cells via receptor-mediated endocytosis or phagocytosis.
Examples include Salmonella interacting with host receptors and inducing membrane ruffling.

Avoiding Phagocytosis

Bacteria evade phagocytes through capsules, leukocidins, preventing phagosome-lysosome fusion, or escaping from the phagosome.

Nutrient Acquisition

Siderophores are small molecules that bind iron, helping bacteria acquire this essential nutrient for growth (e.g., E. coli).

Direct and Toxin-Mediated Damage

Direct damage: Microbes physically damage tissues by releasing enzymes that break down tissue constituents (e.g., Streptococcus pyogenes).
Toxin production involves exotoxins secreted by pathogenic bacteria and endotoxins, parts of Gram-negative cell walls.

Toxin Types

Exotoxins: Protein toxins damaging or destroying host cells, often very potent (e.g., Diphtheria toxin).
Endotoxins: Components of Gram-negative cell walls (LPS), released on bacterial death. These trigger strong inflammatory responses, potentially causing fever, shock, and death (e.g., E. coli LPS).

Mechanisms of Action

A-B toxins: Two-part toxins (A = active, B = binding), damaging cells by disrupting cellular functions.
Membrane-disrupting toxins: Damage host cell membranes.
Superantigens: Cause excessive immune responses by activating large numbers of T cells.
Genotoxins: Damage host cell DNA, leading to mutations and cancer.

Diagnostic Tools

LAL assay: Detects endotoxins (LPS) in pharmaceuticals and medical devices using horseshoe crab blood cells.

Genetic Factors

Plasmids: Carry genes for antibiotic resistance, virulence factors, or toxins (e.g., Shiga toxin in E. coli).
Lysogeny: Bacteriophages integrating their DNA into the bacterial genome, potentially causing toxin production (e.g., Corynebacterium diphtheria).

Causation of Symptoms

Fungal, protozoan, helminthic, and algal diseases’ symptoms arise from toxin production, allergic reactions, tissue invasion, parasite presence, or toxin release.

Portal of Entry vs. Exit

Portal of entry is the site of pathogen entry into the body.
Portal of exit is the site of pathogen exit from the body.

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Description

This quiz explores the key concepts of pathogenicity, including how pathogens enter the body, their virulence factors like ID50/LD50, and mechanisms of adherence to host cells. Test your knowledge on the strategies pathogens use to evade the immune system.