Chapter 21 - Bacterial Pathogenicity Flashcards
pathogen
a microbe capable of causing disease
host
organism being infected
pathogenicity
ability to cause disease - pathogens very in their ability
opportunistic pathogen
a microbe that typically infects a compromised host - such as by weakened immune system or breach to body’s natural defenses
virulence
measurement of pathogenicity - highly virulent more likely to cause disease
Host-pathogen interaction
always changing, and the virulence of a pathogen is important, but so is the number of microbes that gained entry into the host, location, and overall health of the host.
reservoir
natural site of home for a pathogen - can be animate or inanimate
carriers
assist in spreading pathogen from reservoir to a host and then to another infected host - show no signs of the disease
zoonosis
disease that primary occurs w/in animal pops but can be spread to humans
nosocomial infection
hospital-acquired infection
transmission
mechanism by which a pathogen is picked up by a host
direct contact
host-to-host contact - kissing, fucking, where one person is coming into contact w/ another fluids.
Droplet transmission
considered to be direct contact - transmission by respiratory droplets. Droplets are sneezed or coughed by infected and inhaled by a host nearby - not long distances, don’t live long
Indirect contact
transfer through an intermediary such as object or person. example shared toy or doorknob. Also health care worker - 1 pt to another pt
fomite
inanimate object w/ a pathogen on it
Airborne Transmission
pathogens that are small particles or droplets in the environment and remain infectious over time and distance - fungal sports during dust storm
fecal-oral transmission
infected host shedding pathogen in their feces that then contaminates food/water and consumed by next host
vectorborne transmission
when mosquitoes, flies, ticks, are involved. Can be when the vectors picks up agents on external body. However typically is when infectious agent bites and infected host and then spreads it w/ bite on uninfected host.
Virulence Factors
characteristics that contribute to the capabilities of a bacterium to be virulent - such as physical or chemical structures
pathogenicity islands
genes that code for virulence factors - commonly found clustered on pathogens chromosome or plasmid DNA - facilitate sharing of virulence factors between bacteria due to HGT - leads to development of new pathogens over time
how can one distinguish pathogenicity island?
look for G+C content that differs from the rest of the genome - also presence of insertion like sequences flanking the gene cluster
quorum sensing
often controls genes for virulence factors - ensures gene activation when pathogen population is @ optimal density
why is quorum sensing important
triggering genes too soon could alert host’s immune system and cut bacterial infection short
Adherence
adhesion to host cells as well as resistance from phagocytosis - can involve polysaccharide layers made by bacteria (capsule of slime layer) as well as pilus or flagellum
Colonization
After adherence to a surface, a colony is built by increasing in number and utilizing resources available. Important for pathogen survival
Invasion
ability of a pathogen to spread to other locations in the host - when signs/symptoms of a disease will occur
Invasion - what happens during this?
bacterial pathogens produce chemicals (enzymes) that effect host’s cells and tissues.
collagenase.
Enzyme released during invasion - breaks down collagen found in connective tissue
leukocidins
enzyme released during invasion - destroy hosts WBC’s and decrease resistance
Hemolysins
enzyme released during invasion - lyse host’s RBC’s, releasing iron - growth limiting factor for bacteria
bacteremia
bacteria in the blood stream
septicemia
massive, systemic infection (sepsis) and can result in septic shock and death
Toxins
very specific virulence factor produced by some bacterial pathogens - poisonous to the host
Toxigenicity
organism’s ability to make toxins
exotoxin
heat-sensitive soluble proteins released into environment by living organism - associated w/ specific diseases w/ toxin genes often carried on plasmids or by prophages
Type I exotoxin
cell surface-active: bind to cell receptors and stimulate cell response. ex. superantigen
superantigen
type 1 exotoxin - stimulates host T Cells that then produce excessive amount of the signaling molecule cytokine leading to increased inflammation and tissue damage
Type II exotoxin
membrane damaging: exert their effect on cell membrane, often by forming pores. Can lead to lysis as cytoplasmic contents rush out and H2O rushes in, results in disruption of osmotic balance.
Type III exotoxin
intracellular: gain access and stimulate reaction w/in target cell. ex. AB-Toxin
AB-Toxin
Type III exotoxin - composed of 2 units (A + B). B is binding portion of toxin, recognizes and binds to correct cell type. A contains enzymatic activity and is delivered to cell by the B Portion. A portion then acts on the host cell leading to decreased cell function or death. example of AB is tetanus toxin. each AB-toxin is associated w/ different disease.
AB-Toxin on Neuron
A subunit will cleave cellular synaptobreven, resulting in decrease in neurotransmitter release. Results in spastic paralysis of the host.
endotoxin
made by gram negative bacteria as a component of outer membrane. Outer membrane contains LPS and a toxic component (lipid a). Lipid A is heat stable and only released when cell is lysed. - effect is same regardless: fever, diarrhea, weakness, and blood coagulation. Can result in endotoxin shock.
