CH. 25 Microbial Pathogenicity Flashcards
What is pathogenicity? What influences the degree of pathogenicity of a microbe?
Pathogenicity allows the pathogen to cause disease. Virulence genes/factors such as chromosomal, plasmid- or phage-based influence the degree of pathogenicity
What are the different ways in which a pathogen may be transmitted?
Contact:
-Direct: physical contact between source & host
-Indirect: transmission via inanimate object (fomite)
-Droplet: short distance (sneezing, coughing, etc. travels <1 meter)
Vehicle:
-Waterborne: contaminated/water treatment system compromised
-Airborne: dust particles/pet dander
-Foodborne: contaminated food, uncooked food, etc.
Vertical Transmission: mother -> child
Vector:
-Mechanical: passive via body parts
-Biological: involves with parasite life cycle
What is a reservoir? List them
A reservoir is the source of the disease microbes
-Human: shows symptoms of disease or does not (carriers)
-Animal: zoonoses
-Non-Living: soil or water (environmental)
What is meant by portals of entry when referring to an infectious microbe?
It is the way microbes would enter the human
-Mucous Membranes: respiratory tract; gastrointestinal (GI) tract; genitourinary tract
-Skin: hair follicles, sweat glands, conjunctiva
-Parenteral Route: deposition of microbes directly under skin or mucous membrane
What are virulence factors?
Virulence factors are molecular structures that enable microbes/pathogens to cause disease. They consist of the following:
-Adhesins (fimbriae/pili)
-Extracellular enzymes
-Exotoxins
-Endotoxins
-Intracellular pathogens
-Extracellular pathogens (capsule, phase variation)
What are adhesions? What is their function?
Adhesions mediate bacterial attachment to host cells. These occur within:
-Pili/fimbriae
-Glycoproteins
-Non-pili/non-fimbriae proteins
Fimbriae: E coli
M protein: Streptococcus spp
Opa protein: Neisseria spp
What are extracellular enzymes? How do they function as virulence factors? Provide examples of these enzymes
They are enzymes that are secreted by a cell and function outside the cell. They function as virulence factors by controlling the infection and spreading into further tissues within their host
Examples:
-Coagulases: clot blood; isolate bacteria from host
-Kinases: destroy blood clots
-Hyaluronidase: hydrolyzes hyaluronic acid, polysaccharide bridging cells of connective tissue to allow the microbe to spread
-Collagenase: digests collagen in connective tissues (muscles, organs, etc.)
-Proteases: destroy host proteins
What are exotoxins?
Bacteria that can secrete protein toxins into their surroundings that subvert the host function
What are the five classes of exotoxins? Briefly describe each.
Cell membrane disrupters: cause leakage of cell constituents (hemolysins, leukocidin)
Protein synthesis disrupters: target eukaryotic ribosomes (diphtheria, shiga toxins)
Second messenger pathway disrupters: alter ion transport & fluid movement (cholera toxin)
Superantigens: over-stimulate immune system; excess cytokines
Proteases: cleaves specific host proteins (tetanus toxin)
What is the basic structure of such toxins? What is the effect of cholera toxin? of Shiga toxin?
Toxin structure consists of two subunit structures (AB toxins):
-B subunit binds host; A unit contains toxic activity
-Action: destroys specific host cell structures/inhibit metabolic functions (can be VERY lethal)
-Antitoxins: toxoid forms provide immunity
Cholera toxin activates second messenger pathways and Shiga toxins inhibit protein synthesis
What are endotoxins? When and how do these cause their effect?
They are the lipid portion (Lipid A) of the LPS layer of Gram-negative bacteria. They are released when cells die & lyse
-Exert effect by stimulating macrophages to release toxic levels of cytokines
-Can also activate blood clotting proteins and induce fever
-Endotoxic shock: a drastic drop in blood pressure
What is Lipid A?
A lipid component of an endotoxin held responsible for the toxicity of gram-negative bacteria
What strategies do intracellular pathogens have to survive in their host? How do obligate intracellular pathogens differ from facultative ones?
Strategies:
-Breakout of phagosome via hemolysin secretion (Shigella, Listeria)
-Prevent phagosome-lysosome fusion via secretion of proteins (Salmonella)
-Tolerate the phagosome environment (Coxiella burnetii)
Obligate intracellular pathogens must remain inside the host to live and facultative intracellular pathogens can live both outside and inside the host
What strategies do pathogens have to avoid the extracellular immune response?
Some pathogens secrete a thick capsule to cover surface proteins used for recognition/attachment by the host (Streptococcus pneumoniae, Neisseria meningitidis)
Some pathogens make proteins to bind, or to degrade, antibodies (Staphylococcus aureus)
Some pathogens cause apoptosis of phagocytes and others can cause phase variation (altering surface antigens)
What is the purpose of protein secretion as a virulence factor? What is the protein secretion mechanism and what is involved? What is the end result?
“Molecular syringes” in the intracellular pathogens membrane attach & deliver proteins (invasions) to the host cell for the purpose of subverting host functions to their benefit and inducing membrane ruffling (the rearrangment of the cytoskeleton). The end result is that it causes the englufment of bacteria
