Ch. 10 Flashcards
Why can an organism in one host be a pathogen in another?
speculate it is because of disruption in the balance of normal microbiota and host factors
immune system recognizes our normal microbiota, but in some cases….
our immune system mounts a defense against our normal microbiota
examples of normal microbiota that can be also be opportunistic pathogens
Group B streptococci infections (doesn’t affect mother but affects baby). E. coli in the appendix that enters abdominal cavity, and weakened immune system allows yeast infections
tropism
capability of a virus to infect a distinct group of cells in the host. can limit spread of infection in some cases
Does tropism stay the same?
no it can change. 60-80% of new infectious diseases in humans emerged bc of expanded tropism. Ex: HIV, Covid
pathogenicity
ability of a microbe to cause a disease. all or nothing, so pathogen or not
virulence
degree or extent of disease a pathogen causes
what is virulence determined by?
microbe, host, and evolves over time
virulence factors
ways a pathogen is able to overcome host defenses like pathogen toxicity, transmission factors
attenuated pathogen
a weakened, less vigorous virus. can be used to make vaccines that can stimulate an immune response
why is virulence evolving?
because it changes in response to host factors as well as environmental factors.
Infectious does-50 (ID50)
- # of cells or virions in the case of viruses that are needed to establish an infxn in 50% of all exposed susceptible hosts
- more infectious = a lower ID50
- highly infectious does not mean more dangerous
lethal-dose 50 (LD50)
amount of toxin that’s needed to kill 50% of affected hosts that are not treated
LD50 and ID50 can change based on what?
species affected, human immune fitness, route of exposure (inhaled, injected, airborne)
toxins
small amount of molecules that generate a range of adverse effects. can cause tissue damage, suppress immune responses, etc
toxigenic
microbes that make toxins
toxemia
when toxins get in the bloodstream and spread throughout the body
endotoxins
can enter from localized or systemic infections. lipid portion, toxic to us and animals, released when gram-negative bacteria divide or die. if present in sufficient quantities, endotoxins causes septic shock.
the immune system and/or antibiotics kill gram-negative pathogens, which causes…
endotoxemia: endotoxins getting in the bloodstream
exotoxins can be what?
gram pos or gram neg
exotoxins are often classified into three main families based on their mode of action. what are they?
- type 1: membrane acting extracellular toxins. bind but don’t enter the cell (staph and strep)
- type 2: membrane damaging toxins. disrupt or destabilize the cell membrane. cell lyses (hemolysins)
- type 3: intracellular toxins. enter the cell to exert their effects (Pertussis)
toxicity level of endotoxins
lower (relatively high LD50)
toxicity level of exotoxins
higher (many have a low LD50)
5 steps to infection
- Enter the host
- Adhere to host tissues
- Invade tissues and obtain nutrients
- Replicate while warding off immune defenses
- Transmit to a new host
1) enter the host
- portal of entry: any site that a pathogen uses to enter the host. mucous membranes = most common
- some pathogens have more than 1 portal of entry
- portal of entry = often mode of transmission
- site where disease develops (not necessarily the only or main site affected)
integumentary system
blocks most microbes from entering the body. consists of skin, hair, nails, and associated glans
ocular
conjuctiva: enters thru eyes = pink eye
parenteral
enter thru bloodstream, subcutaneous tissues, muscles usually by injections
most common portal of entry
respiratory system. coughs and sneezes = travel through droplets in the air. doesn’t necessarily cause respiratory infections
digestive-system pathogens
frequently have fecal-oral transmission. invade mucosal surfaces of the GI tract
urogenital
sexually transmitted pathogens. enter through the mucosal lining of the vagina/cervix or urethra in men
transplacental entry
vertical transfer of pathogens. mother to baby
- adhering to host tissues
- Adhesins: virulence factors used to stick to host cells in a specific or nonspecific manner
- Bacterial adhesins include: cell wall components, capsules, fimbriae, pili
quorum sensing
a communication mechanism between bacteria that allows specific processes to be controlled, such as biofilm formation, virulence factor expression
- pathogen must invade tissues and obtain nutrients
- Once adhered the pathogen may remain on cell surfaces, reside inside the cell, or invade deeper by passing through or between cells.
- bacteria produce siderophores that snatch iron
- extracellular enzymes: break down nutrients in the local environment and allows pathogens to scavenge nutrients as they damage host tissues
invasins
- allow pathogens to invade host tissues. ex: flagella, collagenases, neuraminidases, coagulases, kinases
- local acting factors
- usually membrane associated or secreted enzymes
mechanism of action for invasins
break down host tissue, form blood clots, allow to replicate, induce host to take up the pathogen, motile
pili and fimbriae are binding factors that are examples of ____, which are virulence factors that allow pathogens to _______ to host tissues
adhesins, adhere/stick
In contrast, flagella and collagenases tend to act as ______ which help pathogens spread deeper into host tissues
invasins
pathogens generate cytopathic effects which…
damage host cells.
- cytocidal: own cells will die
- noncytocidal: damaged not death
Viral pathogens generate cytopathic effects when they:
- invade host cells
- release toxins that can damage cell
- obtaining nutrients
oncogenic pathogen
own host cell that turns to cancer
- pathogen must evade host immune defenses so it can replicate
most pathogens don’t make it this far but can either hide or undermine immune system
hide - intracellular pathogens
spend a majority of their time inside host cells. Ex: viruses
hide - latency
quietly exist inside a host. usually causes persistent or recurrent disease
hide - antigenic masking
pathogen may conceal antigenic features
hide - mimicry
emulating host molecules
hide - variation
periodically altering the surface molecules. immune system doesn’t recognize bc the previous virus changed
undermining the host immune system
immune suppression. pathogens suppress immune function by targeting immune cells, making protases, interfere with transcription of interleukins, interfere with molecular makeup
- pathogen must be transmitted to a new host to repeat the cycle
Symptoms can facilitate transmission to others
Itchiness🡪 scratching bacteria under nails
Coughing/Sneezing 🡪 droplets in the air that spread
Diarrhea 🡪 secretions, frequent bowel movements
portal of exit
route used for exit. often the portal of entry
maintaining a reservoir (source of infxn)
environmental, organism, fomite
biosafety levels are based on what?
level of infectivity, extent of disease caused and mortality rate, mode of transmission, availability of treatment and preventions
BSL-1 agents
very well characterized. rarely cause disease
ex: E.coli
BSL-2 agents
cause disease, not airborne agents, treatable, preventable, vaccines available
Ex: influenza, staph, herpes
BSL-2 plus
dangerous, incurable, no vaccines
Ex: HIV
BSL-3 agents
some are treatable and can be transmitted through the air. serious or lethal human diseases
Ex: mycobacterium tuberculosis, certain influenza strains
BSL-4 agents
no cure, most dangerous, lethal in humans. dangerous and “exotic” pathogens
Ex: ebola
standard precautions used with all patients
hand hygiene, gloves if risk of exposure to wounds, bodily fluids, or mucous membranes, barrier gowns and face shields when splash risk, disinfection
transmission precautions - contact precautions
wound/skin infection, resistant infection, infectious diarrhea
- limit patient transport
- special attention to hand washing
- gloves at all times
- gown at all times
- single patient use equipment
Examples: MRSA, Gram negative antibiotic resistant bacteria, and C. difficile
transmission precautions - droplet precautions
most respiratory infections, influenza, pertussis
- limit patient transport
- procedural mask at all times
transmission precautions - airborne precautions
tuberculosis, rubeola (measles), varicella (chickenpox)
- limit patient transport
- N95 or comparable respirator
- Place patient in Airborne infection isolation room (AIIR) facility
