Chapter 13- Control of microbial growth Flashcards
Microbial spectrum
Refers to how many different types of microorganisms an antimicrobial kills
How clean is clean?
Clean is a relative term. Whether an object or surface is “clean enough” depends on its intended use. Microbial load can be reduced by washing, vacuuming, and dishwashing
What are the negative impacts of sterilization?
Requires time, is labor intensive, can degrade the quality of the item being treated, or have a toxic effect on users
CDC biosafety levels are ranked by
The severity of disease and ease of transmission. There are 4 levels
BSL-1
Microbes are not known to cause disease in healthy hosts and pose minimal risk to workers and the environment. Non Pathogenic strains of E. coli is an example, along with viruses that infect animals other than humans. Few precautions are necessary
BSL-2
Microbes are typically indigenous and are associated with diseases of varying severity. They pose a moderate risk. PPE (lab coat, gloves) are necessary if working with these organisms in the lab, along with an eyewash station and autoclave. Staphylococcus aureus is an example, mumps and measles viruses.
BSL-3
Microbes are indigenous or exotic and cause serious or potentially lethal diseases through respiratory transmission (inhalation). Individuals need to work in biosafety level labs to prevent transmission. Individuals must wear a respirator.
Mycobacterium tuberculosis is an example, so is HIV. Treatment exists for diseases categorized at levels 2 and 3
BSL-4
Microbes are dangerous and exotic, posing a high risk of aerosol-transmitted infections, which are frequently fatal without treatment or vaccines. Few labs are at this level, because they require full PPE (full body suits) and for the lab to be sealed and under negative pressure. Individuals must shower and change clothes when exiting. Ebola and Marburg viruses are examples. Typically, there is no treatment for these organisms
Sterilization
Process by which all living cells, spores, and viruses are destroyed on an object. This is done in medical, laboratory, manufacturing, and food industry settings
Disinfection
The killing or removal of disease producing organisms from inanimate surfaces. It does not necessarily result in sterilization because endospores can remain. Vinegar is a natural disinfectant due to its acidity, while chlorine is a chemical disinfectant used on surfaces
Antisepsis
Similar to disinfection but applies to removing pathogens from the surface of living tissues, such as the skin
Antiseptic
A chemical agent that can be safely used externally on living tissues to destroy microorganisms or inhibit its growth. Neosporin or iodine is an example. Must be able to penetrate deeply without causing tissue damage
Sanitation
Consists of reducing the microbial population to safe levels and usually involves cleaning an object as well as disinfection. Used for food handling equipment and reduces bacterial numbers to meet public health standards. Includes dishwashers, which use hot water and air, resulting in the death of microbes through high temperatures. Hospitals use chemical disinfectants for sanitation
2 classes of antimicrobials
- Cidal agents
- Static agents
Cidal agents
Kill microbes. Bactericidal, algicidal, fungicidal, virucidal, depending on what type of microbe is killed
Static agents
Inhibit or control growth. Bacteriostatic, algistatic, fungistatic, virustatic, depending on what type of microbe is inhibited. These agents are less toxic to humans and can better preserve the integrity of the item that is treated. In an otherwise healthy individual, static agents can be used to treat an infection. The immune system will do the rest of the work to clear the infection
How are disinfectants selected?
- Must be fast acting in the presence of organic materials
- Must be effective against all microorganisms without destroying tissue or acting as a toxin if ingested
- Easily penetrate the material to be disinfected without discoloration or damage
- Easy to prepare and stable in the environment where it is to be used
- Inexpensive and easy to use
- Not have an unpleasant odor
Microbial death curve
Demonstrates the progress and the effectiveness of a disinfectant- shows how many microbes have been killed. When exposed to a microbial control protocol, a fixed percentage of microbes will die regardless of the population size. Therefore, the percentage of microbes killed is more useful information than the actual number. The curve is plotted as a semilog plot
Decimal reduction time (D value)
The amount of time it takes for a specific
protocol to produce a one order-of-magnitude decrease in the number of organisms, or the death of 90% of the population. Ideally, you want at least 90% of the population to be killed
Factors that influence the speed at which lethal damage accumulates (6)
- The initial population size
- Population composition
- Agent concentration or dose of radiation- too high of a concentration is toxic and can degrade the materials
- Duration of exposure to the disinfecting agent
- Presence of organic material (blood, feces) that can inhibit disinfectant action, organic load
- Biofilm formation
How does population size influence the effectiveness of a disinfectant?
The larger the population, the longer it takes to decrease it to a specific number
How does population composition influence the effectiveness of a disinfectant?
Are spores involved? Different types of microbes need different exposure times to the disinfectant
Physical control measures (4)
- Temperature extremes
- Pressure (usually combined with temperature)
- Filtration
- Radiation
What type of heat is very effective at killing microbes?
Moist heat. Heat is the preferred sterilizing agent as long as it doesn’t damage the materials. Heat alters the membranes of microbes and denatures their proteins. Boiling is one example, but it is less effective against endospores and at higher altitudes
Why is dry heat sometimes used to kill microbes?
Dry heat is less effective, but sometimes required- moist heat can oxidize certain materials. Dry heat takes longer to penetrate the cells, so it’s much slower. Examples include incineration or a dry heat sterilizer like an oven
Steam autoclave
Uses a combination of heat and pressure to kill spores and thermophiles. Standard autoclave conditions are 121℃ at 15 psi (pounds per square inch) for 20 minutes. Uses moist heat and is considered the most effective method of sterilization
Thermal death point (TDP)
The lowest temperature that kills all the bacteria in a 24 hour culture after a 10 minute exposure. Some organisms are more heat tolerant than others
Thermal death time (TDT)
Time required to kill all the bacteria in a culture at a specified temperature