Microbial Pathogenesis Flashcards
Pathogen
microbial agent of disease; causes disease by hiding from immune system or using virulence factors to escape/resist
Ectoparasite
lives on surface of host (ex. mosquito)
Endoparasite
lives inside the body of host
Infection
occurs when a pathogen or parasite enters or begins to grow on a host, is measured by infectious dose (ID)
Pathogenicity
the organism’s ability to cause disease
Infectivity
how easily an organism can spread and cause disease
Virulence
measure of disease severity, measured via the infectious dose (ID) and/or the lethal dose (LD)
LD50
the dosage of microbes that will kill half of the infected hosts
Lower LD indicates __________
higher virulence
Primary pathogens
cause disease in healthy host
Opportunistic pathogens
causes disease in immunocompromised hosts
Pathogenicity Islands
where virulence genes are found in chromosomes, plasmids, or phage genomes (contains a cluster of virulence genes)
Carlos J. Finlay
first to identify Aedes aegypti as a vector of yellow fever
Walter Reed
confirmed in 1901 that the mosquito Aedes aegypti is the vector of transmission for yellow fever
To cause disease, all pathogens must….
- Enter a host
- Find their unique niche
- Avoid, circumvent, or subvert normal host defenses
- Multiply
- Transit to a new susceptible host
Type 1 pili adhesion
static attachment to host cell via mannose residues; grow from outer membrane
Type 4 pili adhesion
used by N. meningitidis; continually assembles and disassembles, growing from inner membrane, “twitching motility”
M protein nonpilus adhesion
used by S. pyogenes; binds to fibronectin in the extracellular matrix between host cells for attachment and invasion of tissues; complement regulatory factor H
Pertactin Nonpilus adhesion
used by B. pertussis; binds to host cell integrin for attachment in respiratory tract
Exotoxins
proteins produced by various types of bacteria, kill host cells, and unlock nutrients
Types of exotoxins
Damage cellular membranes (Alpha toxin)
AB Exotoxins (Anthrax, Cholera, and Shiga toxin)
Alpha toxin
found in S. aureus; forms pores in target membranes and red blood cells and causes leakage (responsible for beta hemolysis)
Anthrax toxin
in B. anthracis and consists of Edema factor (raises cAMP levels), Lethal factor (cleaves protein kinases), and protective antigen (binds multiple host cell receptors)
Cholera toxin
made by V.cholerae via lysogenic phage; binds to intestinal cell membranes, trigger endocytosis of cholera toxin complex, and consists of ADP ribosylates a host cell target that leads to sharp increase in cAMP levels, interferes with ion channels, and massive water loss leading to watery stools
Shiga toxin
an AB5 exotoxin produced by Shigella dysenteriae and E.coli O157:H7 that disrupts protein synthesis inhibitors
Endotoxins
found in N.meningitidis, part of LPS of Gram negative bacteria (Lipid A), hyper activates immune system to harmful levels
How does LPS act as an endotoxin for Gram negative cells?
Lipid A is released as Gram negative bacteria die caused a “cytokine storm” and can trigger fever, shock, and death
Three bacterial secretion systems
Type II (pilus like), Type III (syringe like), and Type IV (conjugation system like)
Type 2 Secretion System
- used by P. aeruginosa and V. cholerae; a modification of the same system used for type IV pilis biogenesis
- proteins to be secreted first enter the periplasm, then get folded and secreted via and outer membrane pore
Type 3 Secretion System
- found in Salmonella, Yersenia, Shigella, and Esherichia species
- a reengineered flagellar synthesis mechanism that uses a molecular syringe to inject proteins from the bacterial cytoplasm directly into host
Type 4 Secretion System
- found in A. tumefaciens and B. pertussis
- an evolutionary modification of a conjugation of pilus that secretes protein only, or proteins plus DNA
- allows bacterial pathogens to secrete proteins directly from their cytoplasm or from their periplasms
Extracellular avoidance examples
Capsule: prevents phagocytosis
Protein A: prevents opsonization (S. aureus)
Intracellular avoidance examples
Hemolysin: used to break out of cell once in phagosome (S.dysenteriae, L.monocytogenes)
Prevent fusion with lysosome (Mycobacterium, Legionalla, and Salmonella)
Mature in acidic environment once fused (C. burnetii)
