Host pathogens Flashcards
microbiota
the microorganisms that normally colonize various sites in/within the body without causing disease
resident microbiota
inhabit sites for extended periods
transient microbiota
inhibit temporarily for days, weeks, or months then disappear
colonization
ability of microbe to stay affixed to a body surface and replicate
what does our microbiota do
competitively exclude pathogens
- covering of binding sites prevents attachment
- consumption of available nutrients
- production of compounds toxic to other bacteria
how is microbiota acquired
humans are initially colonized by microorganisms at birth
what can perturb our microbiota
by age 3, a child’s microbiome looks a lot like an adult’s and it becomes much more stable
pathogen
any bacterium, virus, fungus, protozoan, or helminth that causes disease
pathogenicity
the ability of an organism to cause disease
true (primary) pathogens
can cause disease in a host regardless of the host’s resident microbiota or immune system
* are never part of the normal microbiota
opportunistic pathogens
cause disease only under opportunistic conditions
- changes in the composition of the normal microbiota
- can be members of normal microbiota or common in the environment
infection
successful colonization and multiplication of microorganism within a host with or without the manifestation of disease
infectious disease
illness caused by damage to host cells by an infectious agent or its products resulting in signs and symptoms
virulence
degree or severity of disease
lethal dose 50 (LD50)
the number of microbes that kills 50% of an experimental group of animal hosts
infectious dose 50 (ID50)
number of microbes that will cause infection in approximately 50% of an experimental group of hosts
stages of pathogenesis
exposure and entry
adhesion to skin or mucosa
invasion through epithelium and immune invasion
infection
toxins or host immune response
tissue damage, disease
fecal-oral portal of entry
through mucosal surfaces of gastrointestinal transportct
respiratory portal of entry
through musical surfaces of respiratory tract
transplacental portal of entry
through the placenta to infect a fetus
skin portal of entry
through epithelial surfaces
urogenital portal of entry
through mucosal surfaces of genital and urinary tracts
parenteral portal of entry
through injection into the bloodstream (for example, infect bites or needle sticks)
adhesion
fimbriae adhesions
cell wall adhesions
glycocalyzx (slime and capsular polysaccharides)
invasion
ability of some pathogens to spread through tissues
produce enzymes or toxins which serve as virulence factors that allow them to colonize and damage host tissues as they spread deeper into body
immune evasion : antigenic variation
acquire changes in the genes for surface antigens that alter the structure of surface antigens that antibodies would otherwise recognize
virulence factors for immune evasion
capsule
protease
some bacteria resist phagocytic destruction by
preventing fusion of the lysosome with the phagosome
escaping from the phagosome before the lysosome fuses
preventing acidification of the phagosome
resisting killing by lysosomal chemicals
exotoxins
proteins produced by pathogenic bacteria (gram positive and negative) and secreted
endotoxins
lipid A portions of LPS that are part of the outer membrane of the cell wall of gram negative bacteria. they are liberated when the bacteria die and the cell wall breaks apart
exotoxin mode of action: cytolytic toxins
work by disrupting the cytoplasmic membrane integrity, causing cell lysis and death
exotoxin mode of action: AB toxins
consist of two subunits, A and B. B subunit binds host cell receptor and transfers subunit A across the cell membrane and this usually inhibits protein synthesis or disrupts ion homeostasis
exotoxin mode of action : superantigen toxins
overactivate the immune system by activating non specifically CD4+ T cells which leads to an excessive cytokine release and excessive inflammatory response
most genes for exotoxins are carried on
plasmids or phages
body makes antibodies (anitoxins)
provide immunity
inactivate exotoxin (heat, chemical)
toxoid vaccine to stimulate antibody production
in an endotoxin ____ is the toxic part
lipid A
endotoxins only come from gram _
negatie
high/low dose of exotoxin
low
high/low dose of endotoxin
high
are exotoxins release actively or passively from bacteria
actively
are endotoxins released actively or passively from bacteria
passively
endemic
disease consistently present (often as low level) in a population
sporadic
when occasional cases are reported as irregular intervals
epidemic
occurrence of more cases of disease then expected in a given area over a particular period of time
pandemic
an epidemic occurring on several continents and usually affecting an exceptionally high proportion of the global population
prevalence
number of existing cases of disease in a population during a defined period of time
- how much of a population is affected
incidence
number of new cases of disease that vela in a population during a defined period of time
- how quickly are people becoming infected
mortality rate
incidence of death due to a disease during a particular time period
case fatality rate
mortality rate / incidence rate
infectious disease
may or may not be communicable
communicable disease
an infectious disease that is contagious and which can be transmitted from one infected host to another
period of disease
incubation period
prodromal period
period of illness
period of decline
period of convalescence
droplet transmission
close range (within 3 feet)
fomites
inanimate objects that transmit pathogens
droplet nuclei
inhaled by those over a long distance
zoonoses
when a disease comes from animals
acute disease
symptoms develop rapidly
chronic disease
symptoms develop gradually over months or years of lifetime and are slow to resolve
latent disease
the causal pathogen goes dormant for extended periods of time with no active replication. no symptoms unless organism reactivates and infection again becomes acute
