Control of Microbial Growth Flashcards
decontamination/infection
-nuetralization or removal of microbes
-goal is to reduce number/impact of potentially harmful organisms
sterilization
-processing of killing all microorganisms
-sterility can be thought of as binary, its either sterile or it isnt
decimal reduction time
amount of time it takes to reduce number of microbes by a factor of 10
-depends on pH, salt concentration, moisture levels, presence of fats/sugars proteins in samples (can decrease heat penetration)
decima reduction time and food safety
pastuerization
-prevent spoilage and protect against food borne pathogens with certain foods and beverages
-heated for a specific amount of time to eliminate pathogens and to reduce spoiling agents
milk pasteruization time
-71C for 15seconds
-balances between minimal loss of food quality and safety
-not sterilization
-heat resistant lactic acid bacteria survive pastuerization and are what cayse the milk to spoil over time
autoclaves
-sterilization
-use steam to sterilize by heat
-endospores require 121 for 15mins
-water (steam) is pressureized to increase boiling temp allowing it to be 121
-high pressure steam circulated through autoclave
ultraviolet light
-damages DNA and is lethal to microbes at high enough intensities
-useful for sterilizing surfaces or aire, but poor penetrating power
ionizing radiation
improved penetrating power and is used to sterilize surgical supplies labwear and food
filtration
-passing liquids through fiters with pore size of 0.2microns is a common way to sterilize solutions
-high quality filters are very effective but not as reliable as autoclaving
-used for some applications in the lab instead of heat since heat can cause damage
how do many chemical products work (also damage human cells)
-membrane disruption, protein denaturation, oidizing agent
sterilizants
kill microbes
-formadelhyde
disinfectants
-largely for surfaces, kill many/most microbes but not all
-lysol
sanitizers
-similar to disinfectants but less harsh to human also generally less effective
-soaps
antiseptics
-kill or inhibit growth of microbes, non toxic enough to use on tissues
antimicrobial agent
chemical that kills or inhibits the growth of microbes
cidal
-agent that kill cells
-irreversible
static
-agents that do not kill but that inhibit growth
-prevent growth but microbes are not dead and can recover
lytic
-agents that kill cells and cause them to lyse
Minimum inhibitory concentration
-lowest concentration of a compound that fully inhibits microbial growth
-determined using serial dilutions of the compound
zone of inhibition
-antimicrobial activity can also be assessed using solid media combined with disks that contain compound of interest
-disk places on agar plate and diffuses
-closer disk = higher concentration of antimicrobial agent
-the size of the zone of inhibition (area of no growth) indicated suceptibility to compound
-kirby bauer test
antibiotics
-specific mechanisms to taget microbes rather than generic and non specific toxitcityes such as widely inactivating proteins or disrupting membranes
-topical antibiotics are antibiotics in creams
-other antibiotics are typically ingested and must not harm human cells
-generally a small molecule that target specific aspect
alexander fleming
-discovered penecillin from mold on a contamination plate
-also discovered lysozyme
sulfa drugs
first effective ingested Ab was protosil that inhibits folate biosynthesis (folate essential cofactor)
-not effective in test tibe only in live animals as protosil is a pro drug that must be processed by body into its active form (sulphanilamide)
what are the general specific targets that antibiotics target
-cell wall synthesis
-translation, DNA replication, essential biosynthetic processes
how does penecillin work
-inhibits pencillin binding proteins which are proteins that catalyze transpeptidation reaction that crosslink cell wall
-cell wall constanly remodeled in growing bacteria (autolysin proteins)
-penicillin prevents digested wall from being repaired - cell wall loses integrity and cells lyse due to osmotic pressure
where do Ab come from
-microbes produce/secrete antibiotics as competition mechansim
-many AB are natural products isolated from microbes
-Streptomyces (actinomyces) have been a very rich source of Ab
-streptomyces are soil dwelling bacteria that produce large numbers of antibiotics
why does streptomyces have antimicrobial secreting properties
-large genomes, many interesting biosynthetic gene clusters
AMR
-for many pathogens, we are running out o foptions to treat multi-drug resistant strains
4 main mechanisms of resitance
-modification of drug target
-enzymatic inactivation of drug
-preventing access to bacterial cell
-metabolic by pass
how does a microbe become AMR
-altered genetically in a way that reduces sensitivity to Ab
-can occur due to mutation but msot commonly HGT
-improper use of Ab
perisistance
-antibiotc sensitvie populations include rare cells that are transiently tolerance to Ab
-most Ab depend on metabolic activity and often growth in order to be effect, so if your not building a cell wall or inhibitng cell wall synthesis it is not effective
-peristers are genetically unchanged and can be killed bu AB once again after they emerge from tolerant state
dormancy
-is a common route to peristance
Persister vs resister
