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Questions and Answers
What is the main purpose of sterilization?
Which method is specifically known for killing all endospores?
What is the primary mechanism of action for chlorhexidine?
What type of agent is referred to by the suffix '-cide'?
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Which method is NOT a form of sterilization?
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Which of the following is an example of a halogen used as a disinfectant?
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What is the primary purpose of pasteurization?
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What is the function of antisepsis?
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What is the role of iodine in antiseptic applications?
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What type of alcohol is considered most effective for disinfecting?
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Which of the following statements is true about dry heat sterilization?
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What does degerming refer to?
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What is the effect of alcohol on bacteria and fungi?
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Which statement accurately describes quaternary ammonium compounds (quats)?
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Which of the following statements about heavy metals is true?
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Which method is NOT effective as a disinfectant or antiseptic?
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What is the primary role of vacuum filtration in microbial control?
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Which method can result in the killing of some bacteria but not endospores?
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What characterizes the bacteriostatic effect of low temperatures?
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Which type of filtration can remove microbes larger than 0.3 mm?
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What is NOT a characteristic of radiation used for sterilization?
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How do phenolic compounds work as disinfectants?
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The disk diffusion method helps determine the effectiveness of which kind of agents?
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What is the effect of osmotic pressure on microorganisms?
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Study Notes
Control of Microbial Growth
- Sterilization is the complete removal or destruction of all microorganisms and viruses.
- Disinfection is the destruction of most microbes, including pathogens.
- Antisepsis is the disinfection of skin or living tissue, normally using less harsh treatments.
- Degerming is the removal of most microbes from a limited area.
- Sanitization lowers microbial counts to meet public health standards.
Bactericidal vs Bacteriostatic
- -cide agents kill microbes
- -static agents stop the growth of microbes
- Asepsis is an area free of significant contamination
Using Heat to Destroy Microbes
- Heat kills microbes by destroying enzymes and is a bacteriocidal (germicidal) method.
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Boiling for 5 minutes disinfects (not sterilizes) and kills:
- Most pathogenic bacteria (but not all endospores)
- Most viruses
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Pasteurization eliminates pathogens and slows spoilage by heating to:
- Classic treatment: 63°C for 30 minutes
- HTST (High temperature short time): 72°C for 15 seconds
- UHT (Ultra High Temperature): 140°C for 3 seconds
- Destroys all microorganisms that can grow under normal storage conditions.
-
Autoclave sterilizes using pressure (15 psi) and steam (121°C) for about 15 minutes, killing all endospores:
- Used for culture media, hospital instruments, and materials that can withstand heat and moisture.
- All solid surfaces must be exposed to steam and all liquids must reach 121°C.
-
Dry Heat Sterilization uses various methods:
- Direct flaming sterilizes inoculation needles and loops in a microbiology laboratory.
- Incineration is an effective way to dispose of contaminated materials.
- Hot air sterilization uses a drying oven at 170°C for 2 hours to sterilize dry materials that are not temperature sensitive.
Filtration
- Vacuum forces liquids through filters with very small pores (0.1 mm, 0.22 mm, or 0.45 mm).
- Pores are too small for bacteria to pass through.
- Used to sterilize temperature-sensitive liquids like antibiotics, enzymes, and some vaccines.
Air Filtration
- High-efficiency particulate air (HEPA) filters remove microbes larger than 0.3 mm.
- Used in some operating rooms to remove microbes.
Low Temperatures
- Refrigeration slows or stops microbial growth (bacteriostatic).
- Freezing stops microbial growth (bacteriostatic) and only kills a small portion of microbes.
High Pressure
- High pressure treatment may kill many bacteria, but not endospores (bacteriocidal).
- Not a sterilizing method.
Desiccation
- Removal of water (drying) slows or stops growth but usually does not kill microbes (bacteriostatic).
Osmotic Pressure
- High concentrations of salts and sugars create a hypertonic environment which can:
- Kill some bacteria (bacteriocidal or bacteriostatic)
- Molds and yeasts are more resistant
Radiation
- Destroys DNA.
- X-rays and Gamma rays penetrate materials.
- UV and high-energy electron beams are used on surfaces.
Microwaves
- Do not kill microorganisms directly, but heat water.
- High temperatures can be used to disinfect materials.
Chemical Disinfectants
- Most chemical disinfectants can only be used for disinfection, not sterilization.
- The disk diffusion method determines effectiveness by placing a disk of filter paper soaked in a disinfectant on an inoculated agar plate.
- A zone of clearing around the disk indicates the effectiveness of the disinfectant.
Types of Disinfectants and Antiseptics
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Phenolic Compounds disrupt plasma membranes and denature proteins (bacteriocidal):
- Effective and remain active long after application.
- Useful for disinfecting soiled surfaces (saliva, pus, feces).
- Often mixed with other compounds to reduce toxicity.
- Examples include:
- Original formulations of Lysol (household disinfection)
- Hexachlorophene (useful against bacteria causing skin infections in newborns)
- Triclosan (used in personal hygiene products)
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Biguanides attack the plasma membrane (bacteriocidal):
- Chlorhexidine is used to control microbes on skin and mucous membranes.
- Used in surgical hand scrubs and can persist for up to 6 hours.
- Kills some viruses, but does not destroy endospores.
-
Halogens destroy proteins and membranes:
- Used as disinfectants and antiseptics.
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Chlorine forms hypochlorous acid in water and is a strong oxidizing agent that denatures enzymes.
- Examples:
- Household bleach (sodium hypochlorite)
- Chlorine dioxide (sterilizing gas)
- Examples:
-
Iodine is frequently used an antiseptic.
- Examples:
- Tincture of iodine (in alcohol solution)
- Iodophore (linked to a carrier molecule for slow release)
- Examples:
-
Chlorine forms hypochlorous acid in water and is a strong oxidizing agent that denatures enzymes.
- Used as disinfectants and antiseptics.
-
Alcohols denature proteins and disrupt membranes:
- Kill bacteria and fungi, but do not kill endospores or some viruses.
- Act quickly and evaporate.
- Often used for disinfecting surfaces and skin degerming.
- Types used:
- Ethanol (70% most effective)
- Isopropanol (rubbing alcohol)
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Heavy Metals like copper, silver, zinc, and mercury inhibit microbes:
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Silver nitrate (1%) is used as:
- Eye drops for newborns to protect against gonorrheal opthalmia.
- Silver sulfadiazine is a topical cream for burns.
- Silver ions are incorporated into bandages and catheters to slow microbial growth.
- Copper sulfate inhibits algae in reservoirs.
- Mercuric chloride controls mildew in paint (toxic!).
- Zinc chloride is an antiseptic in mouthwashes.
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Silver nitrate (1%) is used as:
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Regular soaps and detergents are not disinfectants or antiseptics, but are important for mechanical removal of microbes:
- Soap breaks up oily deposits and film, allowing water to wash them away along with microbes.
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Quaternary Ammonium Compounds (Quats) are cationic detergents that kill most bacteria, fungi, and some viruses:
- Do not kill endospores or some Gram negative bacteria.
- Strongly antimicrobial, colorless, tasteless, odorless, and non-toxic at low concentrations.
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Description
Test your knowledge on the principles of microbial control, including sterilization, disinfection, and antisepsis. This quiz covers various methods of heat utilization and the differences between bactericidal and bacteriostatic agents. Familiarize yourself with key terms and concepts essential for understanding microbial growth control.
