Pathogenicity and Infection Flashcards
host
larger organism tat supports the survival and growth of a pathogenic microorganism
infection
a microbe growing and multiplying on or within a host
may or may not result in overt disease
infectious disease
any change from a state of health
part or al of the host is incapable of carrying on normal functions due to presence of a pathogen or its products
pathogen
any organism that causes disease
primary pathogen
causes disease by direct interaction with the healthy host
opportunistic pathogen
may be a part of normal microbiota and causes disease when the host is immunocompromised
pathogenicity
ability of a pathogen to cause disease
virulence
degree of harm inflicted on its host
extracellular pathogens
remain in tissues and fluids but never enters host cells during disease
intracellular pathogens
grow and multiply within host cells
two types
facultative intracellular pathogens
reside within the cells of the host or in the environment but can also be grown in pure culture without host cell support
obligate intracellular pathogens
only grow inside of host celss
incubation period
time between pathogen entry and development of signs and symptoms
prodromal stage
mild, non-specific signs and symptoms
illness period
disease is more severe and displays signs and symptoms
convalescence
recovery stage
signs
objective changes that can be directly observed and measured
fever, rash
symptoms
subjective changes, often used in broader score of clinical signs
pain, loss of appetite
disease syndrome
set of characteristic signs and symptoms for a disease
what does the host provide a pathogen?
protection, nutrients, and energy
what are three factors affecting the success of transmission?
virulence of invading organisms
number of invading organisms
presence of adhesion and invasion factors
when does disease ensue?
when organism produces molecules that directly damage the host cells to stimulates host immune cells to destroy infected tissue
animate sources of pathogens
humans or animals
inanimate sources of pathogens
water, food
reservoir
natural environmental location in which the pathogen normally resides
vector
organism that spreads disease from one host to another
what are some examples of vectors?
mosquitoes, ticks, fleas, mites, or biting flies
what are the five main routes of disease transmission?
airborne, contact, vehicle, vector-borne, vertical transmission
what increases efficiency of transmission?
extensive multiplication
tropism
pathogen must make contact with appropriate host tissue determined by specific cell surface receptors
what are the three types of airborne transmission?
droplets (direct)
droplet nuclei (indirect)
aerosols (indirect)
droplets
up to 2 mm in diameter
produced when liquids are placed under force (saliva, mucus, etc)
can travel <1m
droplet nuclei
1-5 um in diameter
result from evaporation of the larger droplets
may remain airborne for hours or days and travel long distances
dust particles
aerosolized, smaller than 1 um can be dispersed even further
microorganisms adhere to dust particles
can survive long periods outside host and can lead to hospital-acquired infections
contact transmission
host touching source or reservoir of the pathogen
what are the two types of contact transmission?
direct and indirect
direct contact
person to person
physical interaction required
touching and sexual contact
indirect contact
involves an inanimate object (fomite) that transfers infectious agent between hosts
vehicles
materials that indirectly transmit pathogens
ex: surgical instruments, drinking vessels, food, water, biological materials such as fluids and tissues, and air
a single source containing pathogens can contaminate a common vehicle that causes multiple infections
vector
living organisms that can transmit a pathogen
most are arthropods (insects, ticks, fleas) or vertebrates (dogs, cats, skunks, bats)
why does the pathogen benefit from vector transmission?
allows for extensive reproduction and spread between hosts
highly virulent and cause diseases such as malaria, rabies, West Nile virus, etc
important that pathogens do not harm their vectors
external (mechanical) transmission
passive carriage of pathogen on body of vector
no growth of pathogen during transmission
internal transmission
carried within vector
harborage transmission
pathogen does not undergo changes within vector
biologic transmission
pathogen undergoes changes within vector
vertical transmission
occurs when the unborn child acquires a pathogen from an infected mother
not as common as horizontal transmission
babies born with an infection disease are said to have a congenital infection
infectious dose (ID50)
number of microbes required to cause disease in 50% of inoculated hosts
varies among pathogen
lethal dose (LD50)
dose that kills 50% of a group of experimental hosts within a specified period
influenced by susceptibility of the host- immune system, nutrition, cleanliness, and emotional health
adherence and invasion
entry and adhesion establish colonization
portal of entry
skin, respiratory, gastrointestinal, urogenital systems, or conjuctiva of the eye
colonization
establish a site of microbial replication on or within host
adherence structures
pili, fimbriae, membrane and capsular materials, specialized adhesion molecules on microbes cell surface
infectivity
ability to create a discrete point of infection
invasiveness
ability to spread to adjacent structures
active penetration
occurs through production of lytic substances that alter host tissue
attack the extracellular matrix and basement membranes of integuments and intestinal linings
degrade carbohydrate-protein complexes between cells
disrupt the host-cell surface
passive penetration
not related to the pathogen itself (skin lesions, insect bites, wounds)
bacteremia
presence of viable bacteria in the blood
septicemia
bacterial or fungal toxins in the blodd
why is clostridium retain considered noninvasive?
it does not spread fro one tissue to the other, but toxins become blood borne
why are bacillus anthraces and plague invasive?
they produce toxins that spread from one tissue to another
formation of actin tail by intracellular bacterial pathogens (listeria, shigella, etc.)
bacteria use cell surface proteins to polymerize host actin
actin tail propels bacteria to the hosts surface where it forms a protrusion
protrusion is engulfed by adjacent cell and evades the immune response
list five ways that successful pathogens elude initial Jost responses and the adaptive immune system?
- survive and replicate inside host cells
- make capsules to avoid phagocytosis
- produce enzymes that inactivate innate resistance mechanisms
- mutate cell surface proteins
- squeeze between host cells
what is phage variation?
switch among different genes that encode similar proteins after pili protein sequence and expressi
how do bacteria suppress host immune response?
infect cells of the immune system and diminish function while ensuring their own survival
some bacteria produce a slippery mucoid capsule that prevents phagocytosis by host immune cells
eliminate O-antigen on LPS to diminish recognition and clearance
biofilm benefits
biofilm bacteria are protected from nutrient deprivation, predators, environmental shifts, antimicrobial agents, and host immune cells
some pathogenic bacteria within biofilms exchange plasmids, nutrients, and quorum-sensing molecules altering their behavior
makes the biofilm community less sensitive to antibiotics and host defense mechanisms
pathogenicity islands
large segments of bacterial chromosomal and plasmid DNA found to encode virulence factors
increase bacterial virulence
absent in nonpathogenic members of same genus or species
genes can be spread from one bacterial cell to another
toxin
substance that disrupts the normal metabolism of host cells
toxigenicity
substance that disrupts the normal metabolism of host cells
intoxications
disease that result from entry of a specific preformed toxin into host
do not require the presence of the actively growing pathogen, just the toxin
exotoxins
soluble, heat-ladle proteins
often travel from the site of infection to other body tissues or target cells where they exert their effects
encoded by genes on plasmids or prophages within bacteria
among the most lethal substances known
types of exotoxins
AB toxin
AB toxin
two subunit types:
-A catalyzes the reaction that causes toxicity
-B binds to host cell receptor
specific site exotoxins
membrane destabilizing
superantigens
superantigens
stimulate about 30% of host T cells of the immune system
causes T cells to overexposes genes that encode cytokine and release pro-inflammatory molecules
results in failure of multiple host organs allowing time for the microbe to disseminate
endotoxin-LPS
gram negative cell wall is toxic to mammals
called endotoxin because it is bound to the bacterium and released when the microorganisms lyses
toxic component is the lipid portion lipid A
endotoxin general features
heat stable
toxic in nanogram amounts
generally similar despite source
cause general system effects
-fever, shock, damage to lining of blood vessels, weakness, diarrhea, inflammation, intestinal hemorrhage, and fibrinolysis
mycotoxins
toxins produced by fungi
aflatoxins
food crop contaminant
produced by aspergillum bacterias
cause chronic and acute liver disease and liver cancer
stachybotrys trichothecene inhibit DNA, RNA, and protein synthesis
induce inflammation, disrupt surfactant phospholipids in the lungs, and may lead to pathological changes in tissues
ergots
produce hallucinogen lysergic acid (LSD)
