lecture exam #3 Flashcards
thermal death point
the lowest temperature at which all microbes in a fluid culture will be killed in 10 minutes.
thermal death time
the minimal time required to kill all the bacteria in a liquid culture at a given temperature.
decimal reduction time
the length in time at which 90% of a bacterial population will be killed at a given temperature.
Kirby-Bauer Test
measures the zone diameter of the ABX compared to a table.
MIC: minimum inhibitory concentration. the smallest effective dose to inhibit growth.
inversely related to the zone of inhibition.
small zone = big MIC : need more chemicals to inhibit growth.
big zone = small MIC : less chemicals needed to inhibit growth.
therapeutic index
the ratio of a drug dose that is toxic to humans compared to the minimal effective dose.
assesses the risks against the benefits.
TI = TD50/ED50
TD50: toxic dose to 50% of the population
ED50: effective dose to 50% of the population.
! safety zone: a larger zone is better for over the counter while a narrow zone must be monitored by the hospital.
ID50
infectious dose.
the dose that will cause an infection to 50% of the population.
measures the virulence.
high ID50: means you need to encounter more microbes in order to get sick. therefore, it is less potent.
low ID50: means you need to encounter less microbes in order to get sick. therefore, it is very potent.
LD50
lethal dose.
the lethal dose for 50% of the population.
measures the amount of toxins released by the microbe that harm the host.
a high LD50 = low virulence. you need a larger volume/dose of the toxin for it to be lethal.
low LD50 = high virulence. you need a smaller volume/dose of the toxin for it to be lethal, very potent!
principles of effective disinfecting
- the concentration of the disinfectant
- organic matter
- pH
- time
enzymes help penetrate host defenses by increasing the virulence of a pathogen.
what are some of those enzymes/functions?
- coagulases - coagulate fibrinogen. coagulase test between staph.
- kinases - DIGEST fibrin clots (break down blood clots)
- hyaluronidase - breaks apart bonds by digesting polysaccharides.
- collagenase - break down the collagen layer to get into deeper tissue.
- IgA protease - destroy igA antibodies
exotoxins vs endotoxins
- endotoxins:
are hydrophilic proteins that come from DNA and are a part of metabolic processes. mostly in gm (+) bacteria. harm over and over due to its enzymatic nature. - exotoxins:
are hydroPHOBIC lipids part of the GM (-) cell wall (lipid A portion) that are NOT part of the metabolic process. are usually released after lysis and cause an immune response to cytokines and coagulation.
the immune response tells the hypothalamus to induce a FEVER!!!
siderophores
use the host’s nutrients!
bind to iron more effectively than human cells do, so they take this nutrient necessary for our red blood cells.
how to pathogens damage host cells?
- using host nutirents
- causing direct damage
- producing toxins
portals of entry:
- mucous membrane:
- respiratory tract: MOST COMMON (common cold, tuberculosis, pneumonia)
- gastrointestinal tract (Hep A and typhoid fever)
- genitourinary tract (STI like chlamydia)
- conjunctiva (around the eye) - skin
- hair follicles
- sweat glands - parenteral
- cuts, open wounds, etc
the 2 methods of microbial control:
- physical: heat and radiation.
- dry heat
- most heat - chemical
where can growth be controlled?
- nonliving
disinfectant/sanitizing (surfaces) and sterilizing (vegetative and endospores) - living
antiseptic
