Microbiology Week 2 Flashcards
What is the purpose of Koch’s postulate?
to identify the organism causing an infectious disease
identifies cause
Tenets of Koch’s postulate
- The organism is found in diseased animal but not healthy
- The organism can be isolated and grown alone
- The organism isolated in pure culture causes the same disease when re-inoculated into suspectible animals
- The organism can be re-isolated
Limitations to Koch’s
Some organisms can’t be grown away from host
Some diseases can be caused by multiple organisms
Carrier states
What is a carrier state?
some animals/humans can be colonized by a pathogen without developing disease
Virulence factors
a factor produced by a pathogen that is important for causing disease
Examples of virulence factors
toxins, adhesins, capsules, etc.
What determines the type of disease a pathogen causes?
Its virulence factors
What is virulence?
the number of organisms it takes to start an infection
the disease producing power of an organism / potency
What should happen with inactivation of the virulence gene?
a measurable loss of virulence
What should happen when wild-type genes are added to an inactive virulence gene?
should restore virulence
Example of virulence factor and pathogen
Cholera toxin is a virulence factor for the bacterium, Vibrio cholerae
What 2 things do successful pathogens need to overcome?
the host defense
the normal flora / microorganisms
infection vs. intoxication
infection is when we introduce actual microorganisms into our bodies
intoxication is when we eat foods containing the toxins of bacteria
in intoxications, we do not consume the actual pathogen. we consume the virulence factors
How does disease actually occur? (2)
damage by directly from pathogen factors or damage from the immune response
Steps of the infectious cycle (6)
- Pathogen enters body
- Pathogen adherence and colonization
- Pathogen invasion through epithelium (sometimes)
- Pathogen evasion of host defenses
- Cell tissue / damage (toxins or immune)
- Dissemination of pathogen so it can infect a new host
Advantages of intracellular pathogen growth
Nutrients are supplies
the pathogen is initially protected from immune system and some antibiotics
Disadvantages of intracellular pathogen growth
Mammalian cells are good at killing invaders
Takes a lot of energy to stay alive intracellularly
2 types of intracellular pathogens
Facultative
Obligate
What are all viruses?
obligate intracellular pathogens
What are most fungi?
Facultative intracellular pathogens
With exception of cryptococcus which is extracellular
What are most protozoa ?
facultative intracellular pathogens
what is another word for protoza?
parasite
What is true of most gram-positive bacteria?
they are extracellular
except for: listeria monocytogenes
Vibrio cholerae
extracellular pathogen
Colonizers
they are good microorganisms
commonly found in the gut and skin
protect against harmful bacteria
Opportunists
organisms normally do not cause harm
at the wrong place and wrong time, can cause disease
example of an opportunist
when inserting a catheter through the skin, staph might be able to get into the bloodstream
Pathogens
organisms that are always harmful to us
Do you italicize viruses?
No
PCR
primer recognition of known viral or bacterial genetic sequences
If a differential diagnosis is infectious, what is the next step to identify?
bacterial, viral, fungal or parasitic
When should you collect a specimen?
ideally before starting antimicrobials
What can cause a false positive when examining microorganisms?
not taking into account the resident microflora
What can cause a false negative when examining microorganisms?
prior antimicrobial use
How do viruses and prions violate Koch’s postulate?
they cannot be cultured on cell-free media
qualitative culture
use for sterile body sites (CSF and blood)
false positives from contamination are common
semi-qualitative culture
helps decide whether the isolated organisms is colonizing or contaminating only
helps to decide if the organism is the cause
Words for infection of bloodstream
Bacteremia or fungemia
What is a common problem with blood cultures?
improperly collected cultures can be contaminated by organisms from the skin’s microbiome
How should blood cultures be collected?
2 sets from 2 different sites
How can you help rule out contamination from the GI tract in urine samples?
absence of epithelial cells (their prescence would indicate contimination)
prescence of white blood cells (indicates infection)
high concentration of organisms
only one kind of bacteria
What can CSF help diagnosis?
meningitis
since CSF bathes the meninges
Meninges
3 layers that surround the CNS
Sputum
a substance spat out from the lower airways (different than saliva)
What can stool help identify?
parasites infecting the gut / gastroenteritis
