Terminology and Methods of Control
- Sterilization–aprocessthatdestroysallviable microbes, including viruses and endospores
- Disinfection–aprocesstodestroyvegetative pathogens, not endospores; inanimate objects
- Antiseptic–disinfectantsapplieddirectlyto exposed body surfaces
- Sanitization–anycleansingtechniquethat mechanically removes microbes, wet cloth, public items
- Degermation–reducesthenumberofmicrobes through mechanical means
Decontamination
Physical, chemical, and mechanical methods to destroy or reduce undesirable microbes in a given area
Relative resistance of microbes
Highest resistance --Prions, bacterial endospores Moderate resistance --Pseudomonas sp. --Mycobacterium tuberculosis --Staphylococcus areus --Protozoan cysts Least resistance --Most bacterial vegetative cells --Fungal spores and hyphae, yeast --Envelope viruses --Protozoan trophozoites
Microbial death
- Hard to detect, Microbes often reveal no conspicuous vital signs to begin with
- Permanent loss of reproductive capability, even under optimum growth conditions
Methods of control(critical, semi critical, noncritical)
Critical-tissue(sterile)
Semi critical-mucosa(disinfectant)
Noncritical-skin(disinfectant)
Selection a method of control depends on circumstances:
- does the application require sterilization
- Is the item to be reused
- can the item withstand heat, pressure, radiation, or chemicals
- Is the method suitable
- Will the agent penetrate to the necessary extent
- Is the method cost and labor efficient and is it safe
Cellular targets of chemical and physical agents
- cell wall–cell wall becomes fragile and cell lyses; some antimicrobial drugs, detergents, and alcohol
- cell membrane–loses integrity;detergent surfactants
- Protein and nucleic acid synthesis – prevention of replication, transcription, translation, peptide bond formation, protein synthesis; chloramphenicol, ultraviolet radiation, formaldehyde
- Proteins – disrupt or denature proteins; alcohols, phenols, acids, heat
Methods of physical control
- HEAT–MOIST AND DRY
- Coldtemperatures
- Desiccation
- Radiation
- Filtration
- heat-Moist and dry
- Moist heat-Lower temperatures and short exposure time, Coagulation and denaturation of proteins
- Dry heat-moderate to high temperatures, dehydration, alters protein structure, incineration
- -bacterial endospores most resistant, usually require temperatures above boiling
- -Thermal death time(TDT)-shortest length of time required to kill all microbes at a specified temp
- -Thermal death point(TDP)-lowest temp required to kill all microbes in a sample in 10 minutes
- -steam under pressure- sterilization
- autoclave(a steam pressure oven)
- Mode of action- denaturation of proteins, destruction Of membranes and DNA
- Tyndalization- intermittent sterilization for substances that cannot withstand autoclaving, 3 day repeat cycle, disinfectant used for some canned foods/lab media
- boiling(not a method of sterilization)-100C for 30min. destroys non endospore forming
- Pasteurization-kills spoilage/infection without destroying flavor/nutritional value-batch method(63-66c for 30min),flash method(71.6c for 15 sec)
- dry ovens coagulate protiens
Methods of physical control
- Heat–moist and dry
- COLDTEMPERATURES
- Desiccation
- Radiation
- Filtration
- Microbiostatic–slows the growth of microbes • Refrigeration- 0–15C and freezing(does not allow microbial growth) <0C
- Used to preserve food, media, and cultures
Methods of physical control
- Heat–moist and dry
- Coldtemperatures
- DESICCATION
- Radiation
- Filtration
- gradual removal of water from cells, leads to metabolic inhibition
- not effective microbial control-Many cells retain ability to grow when water is reintroduced
Methods of physical control
- Heat–moist and dry
- Coldtemperatures
- Desiccation
- RADIATION
- Filtration
Ionizing radiation (low doses mutation, high does fatal)– deep penetrating(preserve food)
power that has sufficient energy to cause electrons to leave their orbit, breaks DNA
– Gamma rays, X- rays, cathode rays
– Used to sterilize medical supplies and food products
Nonionizing radiation – little penetrating power so it must be directly exposed(sterilize water, surfaces)
– UV light creates pyrimidine dimers, which interfere with replication
Methods of physical control
- Heat–moist and dry
- Coldtemperatures
- Desiccation
- Radiation
- FILTRATION
Physical removal of microbes by passing a gas or liquid through filter
Used to sterilize heat sensitive liquids and air in hospital isolation units and industrial clean rooms
Microbial Control(agents, qualities)
• Disinfectants,antiseptics,sterilants, degermers, and preservatives • Some desirable qualities of chemicals: – Rapid action in low concentration – Solubility in water or alcohol, stable – Broad spectrum, low toxicity – Penetrating – Noncorrosive and nonstaining – Affordable and readily available
Levels of Chemical Decontamination
• High-level germicides(cavicide)
–kill endospores;maybe sterilants
– Devices that are not heat sterilizable and intended to be used in sterile environments (body tissue)
• Intermediate-level
–kill fungals pores(not endospores), tubercle bacillus, and viruses
– Used to disinfect devices that will come in contact with mucous membranes but are not invasive
• Low-level
–eliminate only vegetative bacteria, vegetative fungal cells, and some viruses
Factors that affect germicidal activity of chemicals
- Nature of the material being treated(metal, plastic)
- Degree of contamination(blood or vomit on item, presence of organic matter)
- Time of exposure and temp.
- Strength and chemical action of the germicide
Chemical agents used in healthcare(p.338 table)

3 most common halogens(bromine, chlorine, iodine) main two chlorine and iodine
bromine- not volatile, carcinogenic, can’t smell, small amounts in H20
• Chlorine–Cl2,hypochlorites(chlorinebleach), chloramines
– Denaturate proteins by disrupting disulfide bonds – Intermediate level
– Unstable in sunlight, inactivated by organic matter – Water, sewage, wastewater, inanimate objects
• Iodine-I2,iodophors(betadine)
– Interferes with disulfide bonds of proteins
– Intermediate level
– Milder medical and dental degerming agents, disinfectants/ointments
Phenolics(chemical agent, germicide)
• Disrupt cell walls and membranes and precipitate proteins
• Low to intermediate level – bactericidal, fungicidal, virucidal,notsporicidal
– Lysol
– Triclosan – (can cause stunted brain development, for chronic exposure, in makeup/sunscreens) antibacterial additive to soaps
Phenolics(chemical agent, germicide)
• Disrupt cell walls and membranes and precipitate proteins
• Low to intermediate level – bactericidal, fungicidal, virucidal,notsporicidal
– Lysol
– Triclosan – (can cause stunted brain development, for chronic exposure, in makeup/sunscreens) antibacterial additive to soaps
-Used as skin degerming agents for preoperative scrubs, skin cleaning, and burns
alcohols
-optimal dilution 70%
• Ethyl, isopropyl in solutions of 50-95%
• Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi, no resistance bacteria dies or doesn’t
• Intermediate level
Hydrogen Peroxide
-no residue, not stable, only lasts up to 2 months
• Produce highly reactive hydroxyl-free radicals that damage protein and DNA while also decomposing to O2 gas – toxic to anaerobes
• Antiseptic at low concentrations; strong solutions are sporicidal
Aldehydes(power disinfectants)
• KillbyalkylatingproteinandDNA
– Glutaraldehyde in 2% solution (Cidex) used as sterilant for heat sensitive instruments
• High level
– Formaldehyde – disinfectant, preservative, toxicity
limitsuse
• Formalin – 37% aqueous solution • Intermediate to high level
Gases and Aerosols
- Ethylene oxide, propyleneoxide(residue is highly toxic)
- Strong alkylating Air filter agents
- High level
- Sterilize and disinfect plastics and prepackaged devices, foods
Detergents and Soaps
Quaternary ammonia compounds(quats)
- act as surfactants that alter membrane permeability of some bacteria and fungi
- very low level
- soaps- mechanically remove soil/grease containing microbes
