Micro 4: Microbial Pathogenesis Flashcards
What is a pathogen?
a microbe capable of causing disease, especially in immunocompetent people
What is pathogenesis?
the mechanism of disease development
What is virulence?
a measure of a microbe’s ability to cause disease
What is a virulence factor?
any number of products produced by pathogens that allow the microbe to invade, evade host defense, and/or cause disease
What is colonization?
the presence and multiplication of microorganisms with tissue invasion or damage
What is infection?
colonization that generally leads to disease
What is an epidemic?
a disease that rapidly affects many people in a fixed period of time
What is a pandemic
a disease that affects people worldwide
What is an endemic?
a disease that is constantly present at a low level in a certain population
What are primary (frank) pathogens?
microbes that are always associated with disease, regardless of whether the host is immunocompetent or compromised
What are opportunistic pathogens?
pathogens that only cause disease in immunocompromised patients. While the symptoms may appear severe, these pathogens are actually less virulent that primary pathogens because they can only affect compromised individuals
most bacteria fall somewhere in between frank and opportunistic pathogens
What are some of the determinants of infection?
- Number of microorganisms present (innate)
- Virulence of microbe
- Immune status of host (innate)
- Past immune history of the host (adaptive)
What is the initial phase of pathogenesis?
The incubation phase, which consists of the time from the initial contact until the presentation of symptoms of an infection occur. This stage includes: Transmission, in which the host comes into contact with the microbe. This microbe must evade host defenses to colonization and potentially initiate an infection, and many times adherence is a requirement. The localized followed by systemic spread of the infection is the final stage of this phase
What is the difference between prodromal and specific symptoms of an infection?
prodromal symptoms are nonspecific to a particular pathogen and typically precede the presentation of the pathogen induced (specific- i.e. unique to that pathogen) symptoms following infection
What is the most common route of infection for viruses?
respiratory, maybe less so with bacteria. Very hard to control- easy transmission
What are the most common portals of entry for microorganisms into the body?
sites where skin and mucous membranes meet- respiratory, GI, and GU tracts
T or F. Viruses are obligate intracellular pathogens
T.
How do microbes get into cells?
Bacteria and other microbes enter cells through a receptor-mediated endocytosis event. Under normal circumstances, endocytosed material merges with an intracellular phagosome and is transported to lysosomes for breakdown. Pathogens, on the other hand, have evolved mechanisms to evade their destructions. The mechanisms include:
- escape from the phagosome prior to lysosome intervention
- Inhibition of phagosome-lysosome fusion
- blockage of acidification of the enzymes designed to degrade them
What is a Type III secretion system?
exclusive to pathogenic microbes, this system allows the bacterium to introduce its own receptors onto the surface of the target cell, and can then attach to that receptor to mediate its own entry into the cell
What is transcytosis?
a type of transcellular transport in which various macromolecules are transported across the interior of a cell. Macromolecules are captured in vesicles on one side of the cell, drawn across the cell, and ejected on the other side (ex. M cells). This allows bacteria to gain access to subepithelial layers to allow them to enter cells that may not have a receptor on the surface and to spread systemically within the host
Systemic dissemination (spread) of infection commonly occurs through what three routes?
blood, lymph, and CSF. Sometimes, distal damage following systemic spread can be attributed to toxin dissemination rather than the actual spread of the bacteria itself
What are some non-toxin virulence factors used by bacteria to evade phagocytosis and initiate/spread infection?
- capsules
- collagenase and hyaluronidase
- coagulase
- IgA protease
- Protein A
How does the presence of a capsule help pathogenic bacteria evade destruction and promote infection?
capsules are antiphagocytic. There are, however, vaccines that target capsule components in order to break them down and allow for opsonization
What are three examples of pathogenic bacteria that are very dependent on their capsules to initiate an infection?
Str. pneumoniae, H. influenzae, and N. meningitidis
