Explain with examples how successful bacterial infection often depends on structural and enzyme virulence factors.
Answers
Resistance to bacterial infections is enhanced by phagocytic cells and an intact immune system. Initial resistance is due to nonspecific mechanisms. Specific immunity develops over time. Susceptibility to some infections is higher in the very young and the very old and in immunosuppressed patients.Virulence Factors
Virulence factors help bacteria to (1) invade the host, (2) cause disease, and (3) evade host defenses. The following are types of virulence factors:
Adherence Factors: Many pathogenic bacteria colonize mucosal sites by using pili (fimbriae) to adhere to cells.
Invasion Factors: Surface components that allow the bacterium to invade host cells can be encoded on plasmids, but more often are on the chromosome.
Capsules: Many bacteria are surrounded by capsules that protect them from opsonization and phagocytosis.
Exotoxins: Exotoxins include several types of protein toxins and enzymes produced and/or secreted from pathogenic bacteria. Major categories include cytotoxins, neurotoxins, and enterotoxins.
Siderophores: Siderophores are iron-binding factors that allow some bacteria to compete with the host for iron, which is bound to hemoglobin, transferrin, and lactoferrin.