Adenovirus and Host Cell Attachment

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Questions and Answers

What role do bundle-forming pili (Bfp) play in EPEC infections?

They facilitate attachment to the human intestine, leading to severe diarrhea in children.

Identify the primary function of afimbrial adhesins in bacterial infections.

They contribute to tighter binding of bacteria after initial adhesion via pili.

How do uropathogenic E. coli (UPEC) contribute to urinary tract infections?

UPEC strains use specific fimbriae to adhere to the urinary tract lining, leading to infections.

What is the primary role of bacterial adhesins in the context of host cells?

Bacterial adhesins facilitate the binding of bacteria to specific host receptors, enabling colonization. Signup and view all the answers

What types of infections are associated with extraintestinal pathogenic E. coli (ExPEC)?

ExPEC is associated with meningitis and septicaemia in humans. Signup and view all the answers

Describe the structural features of fimbrial adhesins.

Fimbrial adhesins are hair-like structures 5-7nm in diameter, primarily composed of protein subunits called pilin. Signup and view all the answers

What is the significance of pili structure in bacterial pathogenesis?

Pili structure allows bacteria to adhere to specific host cells, which is crucial for infection establishment. Signup and view all the answers

What is the difference between fimbrial and afimbrial adhesins?

Fimbrial adhesins have hair-like structures, while afimbrial adhesins include capsule or protein adhesins that do not have such filaments. Signup and view all the answers

What are the implications of host receptor recognition for bacterial infection?

Host receptor recognition determines the specificity of bacterial adhesion and subsequent infection. Signup and view all the answers

Explain the relationship between pili and bacterial attachment.

Pili act as appendages that allow bacteria to physically attach to host cells and tissues. Signup and view all the answers

Explain the 'lock and key' mechanism in bacterial attachment.

The 'lock and key' mechanism refers to the specific interaction between bacterial adhesins and host cell receptors, allowing for precise binding. Signup and view all the answers

What characterizes the urinary tract infections caused by UPEC?

They involve specific pili types that enable bacteria to adhere to the urinary tract, avoiding urine flushing. Signup and view all the answers

How does the structure of fimbrial adhesins aid in their function?

The diverse structure of fimbrial adhesins enables different types to specifically recognize and bind to various host receptors. Signup and view all the answers

How do affimbrial adhesins and pilus anchorage work together?

Afimbrial adhesins enhance the stability of the bacterial attachment initiated by pili. Signup and view all the answers

What role do UPEC strains play in urinary tract infections (UTIs)?

UPEC strains utilize fimbrial adhesins to adhere to the uroepithelial cells, facilitating the development of UTIs. Signup and view all the answers

In what ways can bacterial and host cells overcome their negative charge to facilitate adhesion?

Bacterial adhesins help circumvent electrostatic repulsion between bacteria and host cells, allowing for adhesion. Signup and view all the answers

Discuss the importance of understanding the pathogenesis of E. coli infections.

It is vital for developing effective prevention and treatment strategies for infections caused by various E. coli strains. Signup and view all the answers

How many human species and serotypes of adenoviruses are known to exist?

There are 7 human species and over 50 serotypes of adenoviruses. Signup and view all the answers

What role do fimbrial adhesins play in bacterial infections?

Fimbrial adhesins help bacteria adhere to host tissues, facilitating colonization. Signup and view all the answers

How do afimbrial adhesins differ from fimbrial adhesins in function?

Afimbrial adhesins do not have the hair-like projections of fimbrial adhesins and mediate adhesion through non-fimbrial structures. Signup and view all the answers

Describe the significance of bacterial pili structure in disease processes.

Bacterial pili, made of protein, are critical for adhesion to host cells and biofilm formation. Signup and view all the answers

What is the relationship between UPEC and urinary tract infections (UTIs)?

Uropathogenic Escherichia coli (UPEC) are the primary cause of UTIs, facilitating infection through their adhesins. Signup and view all the answers

Explain the concept of host receptor recognition in viral infections.

Host receptor recognition involves viruses binding to specific receptors on host cells to gain entry. Signup and view all the answers

What factors determine a virus's host range?

A virus's host range is determined by its capsid or envelope structure and the compatibility with host cell receptors. Signup and view all the answers

What is tissue tropism in the context of viral infections?

Tissue tropism refers to a virus's preference for specific cell or tissue types within the host. Signup and view all the answers

How does the structure of bacterial pili contribute to antibiotic resistance?

The structure of bacterial pili can enhance biofilm formation, providing a protective environment against antibiotics. Signup and view all the answers

In what way do non-fimbrial adhesins aid pathogenic bacteria?

Non-fimbrial adhesins facilitate the attachment of pathogenic bacteria to host cells independently of fimbriae. Signup and view all the answers

Why is understanding host receptor recognition important for developing antiviral therapies?

Understanding host receptor recognition can aid in designing therapies that block viral entry into host cells. Signup and view all the answers

What is the primary structure that makes up the shaft of a pilus?

The shaft of a pilus is composed of repeating protein subunits known as pilins. Signup and view all the answers

Describe the function of the specialized tip structure in some fimbrial adhesins like Pap pili.

The specialized tip structure in Pap pili recognizes specific cells, such as bladder and kidney cells. Signup and view all the answers

Explain how Uropathogenic E. coli (UPEC) causes urinary tract infections (UTIs).

UPEC causes UTIs by using type 1 pilus-mediated attachment to bladder epithelium. Signup and view all the answers

What role do fimbriae/pili play in the disease process of E.coli, particularly in cases of diarrhoea?

Fimbriae/pili enable E. coli to adhere to host tissues, which is critical for establishing infections such as diarrhoea. Signup and view all the answers

How do adhesive subunits along the length of the shaft differ from those with a specialized tip structure in fimbrial adhesins?

Adhesive subunits along the shaft interact with cells via multiple anchorage points, whereas those with a specialized tip recognize specific cell types. Signup and view all the answers

What role do fimbrial adhesins play in microbial colonisation?

Fimbrial adhesins help bacteria adhere to host epithelial cells, facilitating colonisation. Signup and view all the answers

How do afimbrial adhesins differ from fimbrial adhesins?

Afimbrial adhesins do not have long, hair-like structures and are involved in binding at a molecular level. Signup and view all the answers

Describe the basic structure of bacterial pili.

Bacterial pili are slender, hair-like appendages made primarily of protein that extend from the bacterial surface. Signup and view all the answers

What mechanism do UPEC bacteria utilize to cause urinary tract infections?

UPEC utilize fimbrial adhesins to adhere to the urethral and bladder epithelial cells. Signup and view all the answers

What is the significance of host receptor recognition in microbial colonisation?

Host receptor recognition allows pathogens to identify and attach to specific cells within the host. Signup and view all the answers

In what way do bacteria evade mucociliary clearance in the respiratory tract?

Bacteria can adhere to epithelial cells and interfere with the ciliary action, allowing them to bypass mucociliary clearance. Signup and view all the answers

How does the intestinal environment protect against bacterial colonisation?

The intestinal environment is protected by mucus, bile, acidic conditions, and gut flora that prevent pathogen adherence. Signup and view all the answers

What adaptations do pathogens use to overcome host defences in the skin?

Pathogens can invade through layers of dead keratinised skin or penetrate intact skin to overcome host defences. Signup and view all the answers

List one example of a pathogen restricted to epithelial surfaces in the respiratory tract.

Mycoplasma pneumoniae is an example of a pathogen restricted to epithelial surfaces in the respiratory tract. Signup and view all the answers

What defensive mechanism does the urinary tract employ to reduce microbial colonisation?

The urinary tract employs the flushing action of urine to help remove microbes and prevent colonisation. Signup and view all the answers

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Study Notes

Viral Attachment to Host Cells

Viruses require specific receptors to invade host cells.
Adenoviruses: Double-stranded DNA viruses, significant in human respiratory diseases, with 7 species and 50+ serotypes.
Found in mammals, birds, and amphibians.
Attachment through Penton fibers featuring a slender shaft and a globular head; different subtypes target various receptors.

Bacterial Attachment to Host Cells

Bacterial adhesins facilitate binding to host receptors using structures like:
- Fimbrial/pilus adhesins
- Afimbrial adhesins
Mechanism mimics a "lock and key" to overcome electrostatic repulsion between bacterial and host cells.

Fimbrial Adhesins

Bacterial fimbriae: Hair-like structures (5-7 nm diameter) with varying morphology; primarily composed of pilin protein subunits.
Each fimbriae type can recognize distinct host receptors.
Examples include:
- E. coli (causing urinary tract infections, food poisoning)
- Corynebacterium diphtheriae (diphtheria)
- Vibrio cholerae (cholera)

Post-Colonisation Dynamics

After colonisation, pathogens may either stay at the infection site or invade deeper into host tissues.
Notable bacterial pathogens that cross epithelial surfaces include:
- Mycobacterium tuberculosis (respiratory tract)
- Treponema pallidum (syphilis)
- Bacillus anthracis (anthrax)

Host Range and Tissue Specificity of Viruses

Viruses exhibit a host range defined by the organisms they can infect, dependent on their capsid/envelope structure.
Tissue tropism indicates that certain viruses preferentially infect specified cell or tissue types.

Afimbrial Adhesins

These adhesins enhance binding after initial pilus contact with host cells, contributing to more stable adhesion.

Colonisation Overview

Colonisation refers to the establishment of a stable microbial population within a host.
Positive attachment to host cells is critical in initiating infectious diseases.
Primary colonisation sites include:
- Respiratory tract, intestinal tract, reproductive tract, urinary tract, skin, and mucosa.

Host Defenses vs. Microbial Evasion

Hosts employ various defenses, like mucociliary clearance in the respiratory tract and the acidic environment in the intestines, to limit colonisation.
Pathogens have evolved mechanisms to adhere and evade defenses, such as:
- Influenza virus interfering with ciliary action
- Legionella replicating in alveolar macrophages

Key Pathogens and Their Locations

Bacterial pathogens remaining on epithelial surfaces include:
- Mycoplasma pneumoniae (respiratory tract)
- Neisseria gonorrhoeae (urogenital tract)
- Salmonella enterica (intestinal tract).

Fimbrial Adhesins Structure and Function

Fimbriae are composed of helically arranged pilin subunits, with specialized tip structures for recognizing specific host cells (e.g., Pap pili in uropathogenic E. coli).
Fimbrial structure diversity allows for attachment to different tissues, enhancing infection potential.

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