LM 2.1: Intro to Bacteria Flashcards
what are the major steps in the infectious process?
- encounter
- entry
- spread
- multiplication
- damage
- outcome
* spread and multiplication order is interchangable
what is encounter?
agent meets host
birth is usually the first exposure to microbes but there are sme microbes like HIV that can cross the placent
during and shortly after birth we first encounter and establish normal flora = not pathogenic! they actually protect us
what is entry?
agent enters and colonizes the hos
what is spread?
agent spreads from site of entry
what is multiplication?
agent grows in host
what is damage?
agent directly or host indirectly cause tissue damage
what is outcome?
agent wins (death of the host), host wins (elimination of agent) or they tie (coexist)
what are the two types of encounters?
- exogenous encounters
diseases acquired from contact with the environment
ex. catching a cold, food poisoning, tuberculosis etc.
2. endogenous encounters
diseases caused by agents present in/on the body.
ex. a cut leading to staphylococcus infection from staph already on your skin
ex. a ruptured appendix leading to abdominal infection by resident flora
what has increased the encounter of pathogens?
- rise of large dnese human populations (cities)
- increasing trade and transportation
- domestication of animals = zoonotic diseases
what is an infectious dose?
Minimum number of a particular infectious agent required to cause disease
what is ID50?
the dose that causes infection in 50% of a test population
what is LD50?
the dose that causes death (lethality) in 50% of a test population
so if a lower number of bacteria is needed to infect 50%, it would be a better bacteria, more virulent
how does the portal of entry of a pathogen effect the pathogen?
- skin
- inhalation
- ingestion
depending on the route, it changes the ID50 of the pathogen
skin is more infectious than infestion
what re the 2 ways that pathogens can enter the body?
- ingress
2. penetration
what is ingress?
entry of the pathogen into the body cavities that are contiguous with the outside environment
- skin
- internal mucosal epithelia
- GI tract: bladder and pancreas
- respiratory tract
- urinary tract
- peritoneum
- middle ear
what is penetration?
pathogen crossing an epithelial layer into deeper tissues
what are some bacterial infections that do ingress?
- cholera
- pertussis
- diphtheria
- most bladder infectiosn
what are the protective barriers against ingress?
INHALATION
1. larynx and sinuses
- sweeping action of the ciliary epithelium
INGESTION
1. stomach acid
- bile salts
- peristalsis
what are some of the pathogens that infect via penetration?
- hookworm burrows through intact skin on foot
- Salmonella typhi crosses intestinal epithelium
- Streptococcus pyogenes produces exoenzymes that weaken tissue barriers
what are the two categories of pathogen spread?
- lateral propagation
- disseminaiton to distant sites
many host defenses impede both kinds of spreading but many microbial strategies have evolved to overcome those defenses
what is lateral propagation?
a type of pathogen spread
movement from the site of infection to contiguous tissues. Includes cell-to-cell spread
what is dissemination to distant sites?
a type of pathogen spread
movement to remote sites in the body
most commonly happens through the blood (hematogenous)
which diseases don’t have to multiply to cause disease?
so most pathogens need to replicate to cause disease but the exception is diseases caused by prior toxin production (intoxications)
like when the bacteria have preformed a toxin before they’re ingested
ex. food poisoning due to prior toxin
production by Staphylococcus
aureus or Bacillus cereus
what is the incubation period?
time between infection and first symptoms
this is the time that pathogens need to overcome initial defenses and grow
which infection causes damage due to the host response?
H. pylori
ulcer formation due to Helicobacter pylori infection is thought to be due primarily to toxins released by macrophages
which bacteria causes TB?
mycobacterium tuberculosis
TB is successful because it doesn’t make everyone that’s infected get sick!
the sucess come from a tiny fraction of “hits” on people exposed to TB
what is microbe correlation?
whenever we find someone
with a given disease, we find
the suspect bacterium
correlation does NOT prove causation
what is gene correlation?
whenever we mutate a given gene,
the bacterium loses virulence
correlation does NOT prove causation
what is Koch’s postulates 1 and 2?
his postulates in determining is a microorganism is causing a disease are as follows:
the organism is routinely found in lesions of the disease (correlation)
so correlation IS important – it establishes the list of suspects but it is NOT sufficient to “convict” any of them
the organism
can be isolated
in pure culture
on laboratory media from the legions of that disease
what are Koch’s postulates 3a and 3b?
once you isolate the organism you then inoculate experimental
animals with this
isolated organism to see if it
produces the same disease
then you need to make sure the organism can be recovered from the lesions in these experimental animals
what are the limits of the Koch’s postulates?
- In some cases the organism is gone by the time symptoms appear (Lyme disease).
- Some organisms have never been cultured on lab media or even on cell lines (T. pallidum); others rapidly lose virulence factors when cultured on lab media.
- Some organisms only cause a disease in humans (so far as we know).
- Some organisms only cause disease as part of a species group (polymicrobial infections)
nevertheless, where they can be used, Koch’s postulates are still the gold standard of proof.
what are the top 3 infectious diseases that are killing people?
- TB (bacterial)
- malaria (protozoal)
- AIDS (viral)
how big are most bacteria?
1-2 microns
what are the 5 groups of infectious agents?
- viruses
- bacteria
- fungi
- protozoa
- animalia
what are siderophores?
the ability to take up transferrin
this allows the pathogen to get access to iron which it needs to grow
what are qinines?
they are used to kill malarial protozoa
but now we have chloroquin-resistant plasmodium that’s being spread by DDT-resistant mosquitos….lol what have we done
are genetic disease alleles anti-microbial?
the infectious agents aren’t the only thing changing the host-parasite competition!
why do we even have genetic diseases? why weren’t the eliminated via natural selection?
we think it’s because the selective pressure exerted by microbial pathogens is so strong that it has favored the spread of infection-resistance genes, even when those genes are associated with genetic diseases
ex. sickle cell!! because it helps protect against malaria
what is the trade-off model for evolution of virulence?
a less ill, more mobile host is able to infect many others over a longer period of time
