Bacterial Adherence and Virulence

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Questions and Answers

What is the main reason why burns increase the risk of infection?

Physical barrier to microbes is removed (correct)

Inflammation caused by bacterial toxins

Necrosis of skin tissue

Impaired immune defenses due to malnutrition

Which type of stain is commonly used to identify bacteria in tissue samples?

Mucicarmine

Giemsa

Gram (correct)

Silver

What is the best location to visualize microorganisms in a tissue sample?

Area of necrosis

Border of the lesion

Advancing edge of the lesion (correct)

Center of the lesion

Which of the following bacteria can be directly identified in H&E-stained sections?

Candida Signup and view all the answers

What is the role of histopathology in diagnosing infectious agents?

It provides an important clue as to the etiology of the infection Signup and view all the answers

What is the advantage of using specific antibody probes to identify microorganisms?

It enables the identification of microorganisms that are difficult to culture Signup and view all the answers

What is the primary characteristic of suppurative inflammation?

Increased vascular permeability and leukocytic exudates, predominantly neutrophils Signup and view all the answers

Which type of bacteria is typically associated with granulomatous inflammation?

Mycobacterium tuberculosis Signup and view all the answers

What is the term for bacteria that evoke pus formation?

Pyogenic bacteria Signup and view all the answers

What is the result of collections of neutrophils in suppurative inflammation?

Forming abscesses Signup and view all the answers

What is the characteristic of diffuse mononuclear interstitial infiltrates?

Common feature of chronic inflammatory processes Signup and view all the answers

What is the result of untreated acute bacterial infection in a joint?

Destroys the joint in a few days Signup and view all the answers

What type of bacteria typically spares alveolar walls in the lung?

S.pneumoniae Signup and view all the answers

What is the characteristic of the lesions formed by S.aureus and Klebsiella pneumoniae?

Destroy alveolar walls and form abscesses that heal with scar formation Signup and view all the answers

What is the primary function of adhesins on the surface of bacteria?

To bind to host cells and facilitate adherence Signup and view all the answers

Which of the following bacteria produces a neurotoxin that inhibits the release of neurotransmitters?

Clostridium tetani Signup and view all the answers

What is the primary component of the outer cell wall of gram-negative bacteria?

Lipopolysaccharide (LPS) Signup and view all the answers

What is the consequence of high LPS concentration in the host?

Septic shock, DIC, and ARDS Signup and view all the answers

What is the primary function of Toll-like receptor 4 (TLR-4) in the host response to LPS?

Recognition of LPS and triggering of an inflammatory response Signup and view all the answers

Which of the following bacteria is a pyogenic bacterium that produces a fimbriae?

Streptococcus pyogenes Signup and view all the answers

What is the primary function of exotoxins produced by bacteria?

To directly cause cellular injury and disease manifestations Signup and view all the answers

What is the consequence of low LPS concentration in the host?

Activation of T lymphocytes and cytokine production Signup and view all the answers

Study Notes

Bacterial Adherence to Host Cells

Adhesins are bacterial surface molecules that bind to host cells.
Fibrilla cover the surface of Gram-positive bacteria, such as Streptococcus pyogen.
Fimbria (or pili) are filamentous proteins on Gram-negative bacteria, such as E. coli and N. gonorrhea.

Virulence of Intracellular Bacteria

Facultative intracellular bacteria infect epithelial cells, macrophages, or both.
Virulence factors concern the ability to bind and enter cells, and survive within them.
Examples of intracellular bacteria include Shigella, enteroinvasive E. coli, M. tuberculosis, and M. leprae.

Bacterial Endotoxin

Bacterial endotoxin is a lipopolysaccharide (LPS) found in the outer cell wall of Gram-negative bacteria.
LPS is composed of a long-chain fatty acid anchor (lipid A) connected to a core sugar chain.
Free LPS attaches to a circulating LPS-binding protein, which binds to a specific receptor (CD14) on monocytes, macrophages, and neutrophils.
Engagement of CD14 results in intracellular signaling, causing cell activation and production of effector cytokines.

Host Response to LPS

Low LPS concentration: cytokines >> activation of T lymphocytes.
High LPS concentration: cytokines (TNF, IL1, IL12) >> septic shock, DIC, ARDS.

Bacterial Exotoxins

Exotoxins are secreted proteins that directly cause cellular injury and frequently underlie disease manifestations.
Some exotoxins are bacterial enzymes (proteases, hyaluronidases, coagulases, fibrinolysins).
Many exotoxins alter intracellular signaling or regulatory pathways.
Examples of exotoxins include neurotoxins produced by Clostridium botulinum and Clostridium tetani.

Patterns of Inflammatory Responses to Infection

Neutrophil-rich acute suppurative inflammation is typical of many bacteria ("pyogenic" bacteria) and some fungi.
Mononuclear cell infiltrates are common in many chronic infections and some acute viral infections.
Granulomatous inflammation is the hallmark of M. tuberculosis and certain fungi.
Cytopathic and proliferative lesions are caused by some viruses.

Suppurative Inflammation

This pattern is the reaction to acute tissue damage, characterized by increased vascular permeability and leukocytic exudates, predominantly neutrophils.
Collections of neutrophils may give rise to localized liquefactive necrosis, forming abscesses.
The necrotic tissue and inflammatory cells constitute pus, and bacteria that evoke pus formation are called "pyogenic."

Diagnosing Infectious Agents

The histopathology of various infections provides an important clue as to etiology.
Some infectious agents can be directly identified in H&E-stained sections.
Special stains can identify organisms based on their cell wall or cell coat characteristics.
Microorganisms can also be identified after labeling with specific antibody probes.
Organisms are usually best visualized at the advancing edge of a lesion rather than at its center, particularly if there is necrosis.

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Description

This quiz covers the mechanisms of bacterial adherence to host cells, including adhesins, fibrils, and fimbria. It also explores the virulence of intracellular bacteria, including facultative intracellular bacteria that infect epithelial cells and macrophages.