Pathogenic Mechanisms of Bacteria Flashcards
What are the two types of host defenses?
1) Body surfaces.
2) Defenses of tissues and blood.
What is the first line of defense for the body?
Skin and mucosal surfaces.
What are four defenses of the skin?
1) Dry, acidic pH conditions.
2) Low temperature (<37C).
3) Sloughing cells.
4) Resident micro flora.
What is the function of the acidic conditions and low temperature of the skin?
To limit bacterial growth.
What is the function of sloughing cells as a defense?
To remove bacteria from the skin’s surface.
What is the function of the skin’s resident micro flora?
To compete for colonization.
What does SALT stand for?
Skin associated lymphoid tissue.
What cells secrete mucus?
Goblet cells.
How do mucous membranes participate in host defense?
Mucus secreted by goblet cells acts as a lubricant. It acts as a physical barrier that traps bacteria before they reach the membrane itself.
What does mucus secrete?
Secretory immunoglobulin A.
What are three substances that mucus contains that either kill bacteria or inhibit their growth?
1) Lysozyme.
2) Lactoferrin.
3) Lacto peroxidase.
What does lysozyme do?
It splits the muramic acid linkage in bacterial cells and degrades bacterial peptidoglycan.
What type of bacteria is lysosyme extremely effective against?
Gram-positive bacteria.
What does lactoferrin do?
Lactoferrin is a protein that binds iron with a high affinity. Iron is an essential nutrient for bacteria. Most bacteria are unable to compete with lactoferrin for iron. Thus lactoferrin reduces iron availability to bacteria.
Where is lactoferrin found?
Lactoferrin is found in milk and many mucosal secretions, such as tears and saliva.
What is lacto peroxidase?
It has been identified as an antimicrobial agent in milk, saliva, and tears. Lacto peroxidase is toxic to many bacteria.
What does GALT stand for?
Gastrointestinal (gut) associated lymphoid tissue.
What does MALT stand for?
Mucosa associated lymphoid tissue.
What do GALT/MALT do?
They produce secretory antibody which prevents bacterial adherence to mucosal cells.
What are five defensive substances of tissue and blood?
1) Transferrin.
2) PMNs.
3) Monocytes.
4) Macrophages.
5) Complement.
What are four ways bacteria can survive inside PMN’s or macrophages?
1) Strategy to escape phagosome before it fuses with the lysosome.
2) Ability to prevent phagosome-lysosome fusion from occurring.
3) Preventing acidification of the vacuole or short-circuiting the process of fusion itself.
4) Reduce the effectiveness of the toxic compounds released into the phagolysosome after fusion occurs.
What are pathogens?
Pathogens are disease-causing microorganisms.
What is pathogenesis?
It is the physiological processes involved in the generation of clinical signs of disease or the means by which a pathogen causes illness.
What is pathogenicity?
It is the capacity of a microbe to cause disease.
What is virulence?
It is the ability of a microbe to cause disease efficiently (high virulence) or inefficiently (low virulence).
What is a virulence factor?
It is a component of a pathogen that contributes to its disease-producing potential.
What are Koch’s postulates?
1) The organism must always be found in humans/animals with the infectious disease but not found in healthy ones.
2) The organism must be isolated from humans’animals with the infectious disease and grown in pure culture.
3) The organism isolated in pure culture must initiate disease when re-inoculated into susceptible animals.
4) The organism should be re-isolated from the experimentally infected animals.
What is the pathogenic capacity of an organism determined by?
By its virulence factors.
What are five methods by which pathogens cause disease?
1) Adhesion.
2) Colonization.
3) Invasion.
4) Immune response inhibitors.
5) Toxins.
What bacterial species can penetrate the gut epithelial layer?
Salmonella typhimurium.
What are the three routes by which Salmonella typhimurium can penetrate the gut epithelial layer?
1) Salmonellae enter and kill M cells and then infect macrophages and epithelial cells.
2) Salmonellae invade the luminal surface of epithelial cells.
3) Salmonellae enter dendrites of dendritic cells that are sampling the gut luminal contents.
What are M cells?
They are epithelial cells found on the intestinal mucosa.
What do M cells do?
They transport organisms and particles from the gut lumen to immune cells across the epithelial barrier, and thus are important in stimulating mucosal immunity.
What is apoptosis?
It is a form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area.
What are the two major categories that virulence factors can be classified into?
1) Factors that promote bacterial colonization and invasion.
2) Factors that cause damage to the host.
What are five virulence factors that promote colonization and survival?
1) Fimbriae (pili).
2) Nonfimbrial adhesions.
3) Invasins.
4) Motility and chemotaxis.
5) IgA proteases.
What is the best mechanism of adherence?
Attachment mediated by rod-shaped protein structures called pili or fimbriae.
How are cell surface proteins on some bacteria help with adherence?
They mediate tighter binding of bacteria to the host cell.
What are invasins?
Invasins are bacterial surface proteins that provoke phagocytic ingestion of the bacteria by host cells.
How do capsules help bacteria survive?
They protect the bacteria from the host’s inflammatory response (complement activation and phagocyte-mediated killing).
What are siderophores?
Siderophores are low molecular weight compounds that chelate iron with very high affinity.
Why is iron important?
It is essential for bacterial growth and its concentration in nature are generally quite low.
