Chapter 13 - Controlling Microorganisms Flashcards
What are the relative resistances of microbes?
- Highest resistance
- Moderate resistance
- Least resistance
What are the terminology and methods of control?
- Sterilization
- Disinfection
- Antiseptic
- Sanitization
- Degermation
What are three methods used to destroy microorganisms? (decontamination)
Physical, chemical, and mechanical methods
Microorganisms that are targeted usually cause:
Infection or spoilage
What are some examples of microorganisms that are capable of causing infection or spoilage that need to be destroyed?
- Vegetative bacterial cells and endospores
- Fungal hyphae and spores, yeast
- Protozoan trophozoites and cysts
- Worms
- Viruses
- Prions
Microbial death is hard to detect, microbes often reveal no conspicuous _____ _____ to begin with
Vital signs
Microbial death is permanent loss of ____________ capability, even under optimum growth conditions
Reproductive
- Factors that affect death rate
The effectiveness of a particular agent is governed by several factors. What are these factors?
- Number of microbes
- Nature of microbes in the population
- Temperature and pH of environment
- Concentration or dosage of agent
- Mode of action of the agent
- Presence of solvents, organic matter, or inhibitors
- Practical concerns in microbial control
Selection of method of control depends on what 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?
What are the cellular targets of physical and chemical agents?
- The cell wall
- The cell membrane
- Protein and nucleic acid synthesis
- Proteins
What are the methods of physical control?
- Heat
- Cold temperatures
- Desiccation
- Radiation
- Filtration
What are the two modes of action and relative effectiveness of heat?
- Moist heat
2. Dry heat
Lower temperatures and shorter exposure time; coagulation and denaturation of proteins
Moist heat
Moderate to high temperatures; dehydration, alters protein structure; incineration
Dry heat
Bacterial endospores most resistant - usually require temperatures above _______
Boiling
What are the thermal death measurements?
- Thermal death time (TDT)
- Thermal death point (TDP)
Moist heat methods include what two things?
- Steam under pressure - sterilization
- Autoclave - 15 psi/121 degrees C/10-40 minutes
- Steam must reach surface of item being sterilized
- Item must not be heat or moisture sensitive
- Mode of action - denaturation of proteins, destruction of membranes and DNA
Intermittent sterilization for substances that cannot withstand autoclaving
Tyndallization
- Items exposed to free-flowing steam for 30-60 minutes, incubated for 23-24 hours and then subjected to steam again
- Repeat cycle for 3 days
- Used for some canned foods and laboratory media
- Disinfectant
Boiling water at 100 degrees C for 30 minutes to destroy _______________ pathogens
- Disinfection
Non-spore-forming
Heat is applied to kill potential agents of infection and spoilage without destroying the food flavor or value
Pasteurization
- 63-66 degrees C for 30 minutes (batch method)
- 71.6 degrees C for 15 seconds (flash method)
- Not sterilization
___ ____ using higher temperatures that moist heat
Dry heat
What are the two forms of dry heat?
- Incineration
2. Dry ovens
Flame or electric heating coil
Incineration
150-180 degrees C - coagulate proteins
Dry ovens
What are the two forms of cold?
- Microbiostatic
- Refrigeration
- Used to preserve food, media, and cultures
Slows the growth of microbes
Microbiostatic
0-15 degrees C and freezing <0 degrees C
Refrigeration
Gradual removal of water from cells, leads to _________ __________
Metabolic inhibition
Not effective microbial control - many cells retain ability to grow when water is ____________
Reintroduced
Freeze drying; preservation
Lyophilization
Deep penetrating power that has sufficient energy to cause electrons to leave their orbit, breaks DNA
Ionizing radiation
What are some examples of radiation?
- Gamma rays, X-rays, cathode rays
- Cold (low temperature) sterilization
- Used to sterilize medical supplies and food products
Little penetrating power - must be directly exposed
Nonionizing radiation
- UV light creates pyrimidine dimers, which interfere with replication
- Filtration
Physical removal of microbes by passing a ___ or ______ through filter.
Used to sterilize heat sensitive _______ and ___ in hospital isolation units and industrial clean rooms.
- Gas or liquid
- Liquids and air
What are chemical agents in microbial control?
- Disinfectants
- Antiseptics
- Sterilants
- Degermers
- Preservatives
What are 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
What are the levels of chemical decontamination?
- High-level germicides
- Intermediate-level
- Low-level
What are factors that affect germicidal activity of chemicals?
- Nature of the material being treated
- Degree of contamination
- Time of exposure
- Strength and chemical action of the germicide
What are the germicidal categories?
- Halogens
- Phenolics
- Chlorhexidine
- Alcohols
- Hydrogen peroxide
- Detergents and soaps
- Heavy metals
- Aldehydes
- Gases
- Dyes
What are the halogens?
- Chlorine
2. Iodine
Cl2, hypochlorites (chlorine bleach), chloramines
Chlorine
I2, iodophors (betadine)
Iodine
- Disrupt cell walls and membranes and precipitate proteins
- Low to intermediate level - bactericidal, fungicidal, virucidal, not sporicidal
- Lysol
- Triclosan
Phenolics
Antibacterial additive to soaps
Triclosan
- A surfactant and protein denaturant with broad microbial properties
- Low to intermediate level
- Hibiclens, Hibitane
- Used as skin degerming agents for preoperative scrubs, skin cleaning, and burns
Chlorhexidine
- Ethyl, isopropyl in solutions of 50-95%
- Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi
- Intermediate level
Alcohols
- 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
Hydrogen peroxide
- Glutaraldehyde and formaldehyde kill by alkylating protein and DNA
- Glutaraldehyde in 2% solution (Cidex) used as sterilant for heat sensitive instruments
- High level
Aldehydes
- Disinfectant, preservative, toxicity limits use
- Formalin - 37% aqueous solution
- Intermediate to high level
Formaldehyde
- Ethylene oxide, propylene oxide, chlorine dioxide
- String alkylating agents
- High level
- Sterilize and disinfect plastics and prepackaged devices, foods
Gases and aerosols
What is 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
- Ethylene oxide, propylene oxide, and chlorine oxide
- Strong alkylating agents
- High level
- Sterilize and disinfect plastics and prepackaged devices, foods
Gases and aerosols
- Quaternary ammonia compounds (quats) act as surfactants that alter membrane permeability of some bacteria and fungi
- Very low level
Detergents and soaps
Mechanically remove soil and grease containing microbes
Soaps
- Solutions of silver and mercury kill vegetative cells in low concentrations by inactivating proteins
- Oligodynamic action (little power)
- Low level
- Merthiolate, silver nitrate, silver
Heavy metals
- Aniline dyes are very active against gram-positive species of bacteria and various fungi
- Sometimes used for antisepsis and wound treatment
- Low level, narrow spectrum of activity
Dyes as antimicrobial agents
- Low level of activity
- Each are a narrow spectrum
- Each effect something specific
Acids and Alkalis
