bacterial pathogenicity Flashcards
What is the difference between pathogenicity and virulence, and how can a single organism exhibit different levels of virulence?
Pathogenicity refers to the ability of an organism to cause disease, while virulence indicates the severity or degree of harm the organism causes. Different environmental conditions, host factors, and bacterial load can influence the level of virulence an organism exhibits.
What are the main steps in the life cycle of a pathogen, and how does each step contribute to disease progression?
The steps include transmission, colonization, invasion, proliferation, and re-transmission. Each step allows the pathogen to enter, survive, multiply, and spread, ensuring both its survival and the progression of infection.
How do bacteria adhere to host tissues, and why is this important for colonization?
Bacteria use adhesins (proteins or polysaccharides) to bind to receptors on host cell surfaces. This is crucial for colonization because without adherence, bacteria cannot establish themselves in the host and may be cleared by immune responses.
What are bacterial adhesins, and how do they interact with host cell receptors?
Bacterial adhesins include fimbrial proteins, surface proteins, and polysaccharides (capsules, teichoic acids). They interact with host cell receptors via protein-protein or protein-carbohydrate interactions, allowing bacteria to attach firmly to host tissues.
Explain the difference between extracellular and intracellular bacterial invasion. What are the benefits for pathogens using each strategy?
Extracellular invasion involves breaking down tissue barriers with enzymes, allowing bacteria to spread to new tissues. Intracellular invasion allows bacteria to hide inside cells, avoiding immune detection and sometimes exploiting host cellular machinery for replication.
Describe how intracellular bacteria invade non-phagocytic cells and provide an example of this process.
Intracellular bacteria, such as Salmonella or Pseudomonas, use a secretion system to inject invasion proteins into non-phagocytic cells, recruiting host proteins like actin to induce a phagocytosis-like process. This allows the bacteria to enter and survive inside the host cells.
What are the main virulence factors that contribute to bacterial pathogenicity, and how does each one function?
Virulence factors include adhesion (to colonize host cells), invasion (to penetrate tissues), evasion of host defenses (to avoid immune response), obtaining nutrients (to survive), and toxicity (to damage host cells). Each factor supports the pathogen’s ability to establish and maintain an infection.
How does a pathogen’s infectious dose (ID50) and lethal dose (LD50) relate to its virulence
The ID50 is the amount of pathogen needed to infect 50% of hosts, while the LD50 is the amount needed to kill 50% of hosts. Lower ID50 and LD50 values indicate higher virulence, as it takes fewer pathogens to cause infection or death.
What role do extracellular enzymes like proteases and glycanases play in bacterial invasion, and why are they important for spreading infections?
These enzymes break down components of the extracellular matrix and the cell junctions between host cells, allowing bacteria to penetrate deeper into tissues, access nutrients, and evade immune barriers, thereby spreading infection.
What are the key factors that determine whether a pathogen will cause disease after transmission?
Key factors include pathogenicity and virulence of the organism, transmission routes, the pathogen’s ability to adhere to and invade host cells, and the host’s immune response.
Compare direct and indirect transmission of pathogens and give an example of each.
Direct transmission involves immediate contact between hosts (e.g., respiratory droplets in tuberculosis). Indirect transmission occurs via intermediaries like contaminated objects or vehicles (e.g., contaminated food causing Salmonella infections).
How do fimbriae contribute to the pathogenicity of Escherichia coli in urinary tract infections (UTIs)?
Fimbriae on E. coli, such as P-pili or Type I pili, bind to sugar moieties (globobiose, mannose) on glycolipids of epithelial cells lining the urinary tract, allowing the bacteria to adhere, resist flushing by urine, and establish infection.
What are the different transmission routes for pathogens, and how do they influence the spread of disease?
Transmission routes include respiratory (e.g., influenza), faecal-oral (e.g., Salmonella), body fluids (e.g., HIV), and indirect via fomites or vehicles (e.g., contaminated water in cholera). The route affects how quickly and broadly a pathogen can spread.
Why are mucosal surfaces more favorable for pathogen entry than the skin, and what makes them an ideal site for infection?
Mucosal surfaces are warm, moist, and rich in nutrients, providing a more hospitable environment for pathogens. Additionally, the immune defenses at mucosal sites are often less effective than the physical barrier of healthy skin.
How do bacterial pathogens use host immune cells, such as phagocytes, to their advantage during intracellular invasion?
Some pathogens invade and survive within phagocytes by resisting digestion in the phagolysosome or modifying it, allowing them to use the host cell as a niche for replication and spread without being detected by the immune system.
