Final: Ch 9: Physical & Chemical Control Flashcards
4 techniques for controlling microorganisms
sterilization
disinfection
decontamination (sanitization)
antisepsis
Sterilization
kill/remove all microorganisms (including endospores) in a material/object
ex. autoclave or chemical sterilants
Disinfection
remove vegetative bacteria (not endospores)
ex bleach, iodine, boiling
Decontamination (sanitization)
mechanical removal of microorganisms/other debris to reduce contamination to safe levels
ex. soaps, detergents
Antisepsis “degerming”
reduces the # of microbes on the human skin
decontamination on living tissues
ex. alcohol, surgical hand scrubs
Sepsis
the growth of microorganisms in the blood and other tissues
Antiseptics
chemical agents applied directly to exposed body surfaces to prevent vegetative pathogens
skin and mucous membranes, wounds, and surgical incisions
- prepping skin before surgical incisions
- swabbing an open sore
- ordinary hand washing w/a germicidal soap
Chemicals can be used to kill or inhibit microbial growth (few chemicals achieve sterility)
chemical agents are used on living tissues (as antiseptics) and on inanimate objects (as disinfectants)
3 Major principles of microbial control
- a definitive proportion of the organisms die in a given time interval
- not all microbes die immediately - the fewer organisms present, the shorter the time needed to achieve sterility
- microbes differ in their susceptibility to antimicrobial agents
- need to match antimicrobial agents appropriately
Effectiveness of control depends on (factors):
of microorganisms
target population (bacteria, fungi, spores, viruses)
temp
pH
concentration of agent
mode of action (what is it attacking?)
interfering agents (solvents, debris, saliva, blood, feces)
Microbial death
microbial death = when they are no longer reproducing (permanent loss of reproductive capability even under optimal conditions)
they can still be metabolizing and stuff but if they arent reproducing = dead
Targets to control microbial presence
injure cell wall injure cell membranes interfere w/nucleic acid synthesis interfere w/protein synthesis interfere w/protein function remove microbes
Target: Cell wall
bacteria and fungi: -block synthesis -degrade cellular components -destroy or reduce stability Agent: -chemical: penicillin, detergents, alcohols -physical: heat and radiation
Target: cell membrane
All microbes and enveloped viruses: -bind and penetrate lipids -lose selective permeability (leakage) Agent: -chemical: surfactants -physical: heat and radiation
Target: nucleic acid synthesis
irreversibly bind to DNA: -stop transcription and translation -cause mutations Agent: -chemical: formaldehyde -physical: heat and radiation
Target: protein synthesis
Binds to ribosomes: -stops translation -prevents peptide bonds Agents: -chemical: chloramphenicol -physical: heat and radiation
Target: protein function
Block protein active sites Prevent binding to substrate Dentature protein Agent: -chemical: alcohols, acids, phenolics, metallic ions -physical: heat and radiation
Physical control methods: temperature and radiation
Temp -moist heat -dry heat -cold Radiation -ionizing -ultraviolet
Killing with heat: oxidize and denature
most common method of sterilization
modes of action:
-oxidize & denature
Effectiveness varies with: kinds of microbes, their number, intensity, length of exposure, pH, moisture, nature of product
Moist heat sterilization
most common and efficient method 2 kinds: -boiling -steam sterilization (autoclave) moist heat is much hotter than dry (100 degrees in Oregon feels much hotter than in Arizona)
Boiling
effective on glassware and instruments
kills fungi, protozoa, bacteria, viruses in 10-30 min
requires 3 separate boilings to kill endospores
Pros: can use at home
Cons: messy, time consuming, materials may require drying, endospores may require longer time
Steam sterilization (autoclaving)
uses: liquids, glassware, instruments, bandages, contaminated material
steam must reach all surfaces to be effective
most efficient and convenient
kills all microbes in 15-20 min
materials may need drying
Dry heat
types: -oven (hot air) sterilization -flaming inoculating loops -incineration/burning Temp and time of exposure is greater than moist heat
Ovens
heat at 160-170 c for 2 hrs
kills microbes and endospores by oxidation or denaturation
used on glassware and instruments
cant be used on liquid media, cloth, plastics or articles wrapped in paper
Incineration
destroys contaminated materials: -blood soaked swabs, bandages -contaminated materials and objects -entire diseased animal carcasses safe and effective
Thermal death time (TDT)
shortest length of time required to kill all test microbes at a specified temp
Thermal death point (TDP)
lowest temp required to kill all microbes in a sample in 10 minutes
Radiation
movement of energy in waves thru space and materials
high frequency = greatest penetrability
-waves strike molecules and knock out electrons
-releases ions and creates free radicals in cells
-ions attach to proteins and nucleic acids, damage cell structures, cause cell death
kills microbes on surfaces and within materials
good for heat sensitive items
UV radiation
moderate wavelengths = low penetrability
wont penetrate paper glass or skin
kills microbes on surfaces
cross links DNA, inhibits replication, not safe to use on skin, causes burns and cancer
uses: sterilizes surfaces in labs and operating rooms; also vaccines, serum, toxins, drinking water and waste water
germicidal lamp in hospitals, schools, food prep areas
High energy Ionizing radiation
gamma rays, x rays, electron beams
gamma rays use to sterilize glassware, surgical instruments, sterile drapes
electron beams used to sterilize pharmaceuticals, disposable plastic syringes, surgical gloves, etc
Mechanical control methods
filtration:
- liquid
- gas
Filtration
the passage of liquids and gases thru screen-like material w/pore sizes small enough to retain microbes
removes microbes - doesnt kill or inhibit them
used to sterilize air and heat sensitive material
gases are forced thru under positive pressure
liquids are either forced thru under pressure or pulled thru under vacuum
fluids are collected in sterile vessels
Uses of filtration
heat sensitive material
removes bacteria, but not viruses, from plasma
Air filtration
used in operating rooms, burn units, laminar flow hoods in high security pathogen
use high efficiency particulate air (HEPA)
Chemical Agents
Range from disinfectants and antiseptics to sterilants ad preservatives
Aqueous solutions
Tinctures
Aqueous solutions (chemical agents)
chemicals dissolved in pure water as the solvent
Tinctures (chemical agents)
chemicals dissolved in pure alcohol or water-alcohol mixtures
Chemical agents: Principles of Effective distribution
pay attention to the properties and concentration of the disinfectant
consider: the presence of organic matter, degree of contact with microorganisms, and temp
Chemical agents: Qualities that an ideal disinfectant should have
antimicrobial activity solubility stability lack of toxicity for humans and animals minimum activity by extraneous material activity at ordinary temps ability to penetrate material safety availability and low cost
Chemical agents: how do you know if a disinfectant works?
Test it!
serial dilution test
disk diffusion test
Chemical agents: Serial-dilution test
calculates # of surviving microbes after 10 min in disinfectant solution
the MIC
Minimum inhibitory concentration (MIC)
the concentration required to inhibit growth of a specific isolate in vitro under standardized conditions
determined by finding the lowest dilution w/out visible growth during serial dilution testing
will vary for individual isolates
Chemical agents: Disk diffusion test
filter paper disk is soaked w/disinfectant/antibiotic and applied to inoculated plate
look for inhibited growth
Chemical agents: Types of chemical control agents
Phenols
Phenolics
Halogens: Iodine, chlorine
Alcohols
Heavy Metals
Quaternary Ammonium Compounds (Quats): Zephiran, cepacol
Chemical food preservatives: sodium dioxide, sodium benzonate, sodium nitrate
Aldehydes
Gaseous Chemosterilizers: ethylene oxide
Peroxygens: hydrogen peroxide, benzoyl peroxide, peracetic acid
Controlling microbes in the lab: Refrigeration & Freezing
Bacteriostatic: inhibits growth and toxin production
slow freezing kills many microbes, but not all
survivors multiply when returned to growth temps (toxins produced previously are not affected)
not a sterilant
Controlling microbes in the lab: Desiccation
at ambient temps essentially bacteriostatic -kills many microbes (species sensitive) -used to prepare foods, meats -not a reliable sterilant!! Does not kill endospores and protozoan cysts
Controlling microbes in the lab: Lyophilization
slow freezing under vacuum
removes water w/out ice crystal formation in cells = avoids cell damage
used to store bacteria and viruses as POWDERS
lyophilized microbes can be rehydrated and grown in culture
Controlling microbes in food: Microwave radiation
kills bacteria by heating
unreliable sterilant!!!
- ovens have “cold spots”
- materials must be rotated to achieve even temp distribution
- wont kill Trichinella cysts
a new version for labs sterilizes media in 10 min
Controlling microbes in food: Osmotic pressure
adding large amounts of salt or sugar to foods creates a hypertonic environment for bacteria - causes plasmolysis
pickling, smoking, and drying foods have been used for centuries to preserve
osmotic pressure is never a sterilizing technique!!!
Controlling microbes in food: Pasteurization
Disinfection of beverages
stops fermentation
mild heat (71) used to kill pathogens and reduce microbe populations
prevents transmission of milk-borne diseases
need to maintain taste and appearance
Controlling microbes in food: Gamma Rays
kills bacteria in food
eliminates insects
prevents premature sprouting of seeds
extends shelf life
used on poultry, pork, fresh fruits, white potatoes, spices
may discolor food and/or alter taste
animals fed irradiated feed lose weight
no demonstrated risk from residual radiation
6 factors that affect the action of antimicrobial agents
- # of microbes
- target population
- temp pH
- concentration of agent
- mode of action
- interfering agents
High decontamination
types of microbe killed: endospore
applications: medical devices
Medium decontamination
types of microbe killed: fungal spores, viruses, resistant pathogens
applications: disinfect items that come into contact with mucous membranes, but are non invasive
Low decontamination
types of microbes killed: vegetative bacteria, vegetative fungal cells, some viruses
applications: clean electrodes, straps and pieces of furniture that touch skin surfaces but not mucous membranes
