![➢ DISINFECTION - refers to the use of physical or
chemical agents known as disinfectants, including
ultraviolet light, heat, alcohol, and bleach, to inhibit or
destroy microorganisms, especially pathogens.
• It is a process that reduces the number of viable
microorganisms to an acceptable level but may not
inactive some viruses and bacterial spores.
• When a chemical is used on skin or other tissue, the
process is called ANITISEPSIS, and the chemical is
called an ANTISEPTIC [Disinfection of living tissues is
antisepsis]
• Antiseptics and disinfectants often have the same
components, but disinfectants are more concentrated or
can be left on a surface for longer periods of time. Of
course, some disinfectants, such as steam or
concentrated bleach, are not suitable for use as
antiseptics.
➢ANTISEPSIS - the destruction or inhibition of micro-
organisms on living tissues by application of an antiseptic
solution.](https://image.slidesharecdn.com/lecture4controllingmicrobialgrowthintheenvironment-part1-250427082536-a4cbfd4c/85/Lecture-4-Controlling-Microbial-Growth-in-the-Environment-Part-1-pdf-8-320.jpg)
Lecture 4 Controlling Microbial Growth in the Environment- Part 1.pdf
- 1. Lecture 4 – Part (1): Controlling Microbial Growth in the Environment
- 2. ❑ Learning Outcomes: 1. Differentiate among , cleaning, asepsis, antisepsis, disinfection, sterilization, degermination, sanitization, decontamination, and explain their practical uses. 2. Describe the factors that need to be considered before deciding on the most appropriate method to be used for microbial control.
- 3. ❑ Learning Outcomes: 4. Identify the two most resistant groups of microbes, and explain why they are resistant to many antimicrobial agents. 5. Describe how antimicrobial agents act against cell walls, cytoplasmic membranes, proteins, and nucleic acids. 6. Describe the different physical methods that can be used in the control of microbial growth.
- 6. ❑ Introduction The control of microbes in health care facilities, in laboratories, and at home is a significant and practical aspect of microbiology. In this chapter, we study the terminology and principles of microbial control, the factors affecting the efficacy of microbial control, and various chemical and physical means to control microorganisms and viruses.
- 7. ❑ Terminology ➢ CLEANING - It is a process that removes visible contamination but does not necessarily destroy micro organisms. It is necessary prerequisite for effective disinfection or sterilization. ➢ ASEPSIS -Term used to describe methods which prevent contamination of wounds and other sites, by ensuring that only sterile objects and fluids come into contact with them. ➢ Examples of surgical asepsis include the use of disposable sterile supplies, such as syringes, needles, and surgical gloves. Asepsis (Noun) Aseptic (Adjective)
- 8. ➢ DISINFECTION - refers to the use of physical or chemical agents known as disinfectants, including ultraviolet light, heat, alcohol, and bleach, to inhibit or destroy microorganisms, especially pathogens. • It is a process that reduces the number of viable microorganisms to an acceptable level but may not inactive some viruses and bacterial spores. • When a chemical is used on skin or other tissue, the process is called ANITISEPSIS, and the chemical is called an ANTISEPTIC [Disinfection of living tissues is antisepsis] • Antiseptics and disinfectants often have the same components, but disinfectants are more concentrated or can be left on a surface for longer periods of time. Of course, some disinfectants, such as steam or concentrated bleach, are not suitable for use as antiseptics. ➢ANTISEPSIS - the destruction or inhibition of micro- organisms on living tissues by application of an antiseptic solution.
- 9. ➢ STERLIZATION - it is the process of destruction or removal of all microorganisms, including viruses and bacterial endospores from surface or medium, including spores. • When all forms of microbial life, including endospores are eliminated. • In practical terms, sterilization indicates only the eradication of harmful microorganisms and viruses.
- 10. ➢ DECONTAMINATION -process that removes pathogenic microorganisms from an object to make it safe to handle. The level of microbial contamination is reduced enough that it can be reasonably assumed free of risk of infection transmission. Disinfection, antisepsis, and sterilization are forms of decontamination. Decontamination Disinfection Antisepsis Sterilization
- 11. ➢ SANITIZING - is the process of disinfecting places and utensils used by the public to reduce the number of pathogenic microbes to meet accepted public health standards. Example: sanitize restaurant utensils and dishes, and chemicals are used to sanitize public toilets. ➢ Degerming is the removal of microbes from a surface by scrubbing, such as when you wash your hands or a nurse prepares an area of skin for an injection. ➢ GERMICIDE Any chemical agent that kills microorganisms (Such as any antiseptic or disinfectant agents)
- 12. ➢ PASTEURIZATION Using heat to kill vegetative bacteria and reducing the number of microbes that have the potential for food spoilage
- 13. So far, we have seen that there are two major types of microbial control—sterilization, which is the elimination of all microbes, and antisepsis or disinfection, which each denote the destruction of vegetative (nonspore) cells and many viruses.
- 14. Table 9.1 Terminology of Microbial Control
- 15. ❑ The Selection of Microbial Control Methods • Ideally, agents for the control of microbes should be: • Inexpensive • Fast-acting • Stable during storage • Capable of controlling microbial growth while being harmless to humans, animals, and objects. Unfortunately, such ideal products and procedures do not exist—every agent has limitations and disadvantages.
- 16. ❑ The Selection of Microbial Control Methods • Factors Affecting the Efficacy of Antimicrobial Methods 1. Site to be treated • Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects • Moreover, when performing medical procedures, medical personnel must choose a method and level of microbial control based on the site of the procedure because the site greatly affects the potential for subsequent infection. • Example on the next slide.
- 17. ❑ The Selection of Microbial Control Methods • Factors Affecting the Efficacy of Antimicrobial Methods For example, the use of medical instruments that penetrate the outer defenses of the body, such as needles and scalpels, carries a greater potential for infection, so they must be sterilized; however, disinfection may be adequate for items that contact only the surface of a mucous membrane or the skin. In the latter case, sterilization is usually required only if the patient is immunocompromised.
- 18. • Factors Affecting the Efficacy of Antimicrobial Methods 2. Relative susceptibility of microorganisms Germicide classification In 1972, Dr. Earl Spaulding proposed a system for classifying liquid chemical germicides and inanimate surfaces and proposed a system called: “The Spaulding Classification System” Which has subsequently been used by the CDC, the FDA (Food and Drug Administration), and opinion leaders in the United States. ❑ The Selection of Microbial Control Methods
- 19. • Factors Affecting the Efficacy of Antimicrobial Methods 2. Relative susceptibility of microorganisms Germicide classification • Spaulding’s classification system categorizes: ➢Disinfection level: sterilization, high-level disinfection, intermediate-level disinfection, and low-level disinfection. ➢Items: Critical, semi-critical & non-critical. The degree of risk for patient infection from contamination involved in the use of the items or equipment ❑ The Selection of Microbial Control Methods
- 20. The Spaulding Classification System
- 21. CRITICAL • Critical items are those associated with a high risk of infection if the items are contaminated with any microorganism, including bacterial spores. This category includes: • Surgical instruments • Cardiac and urinary catheters • Implants • Ultrasound probes used in sterile body cavities
- 22. CRITICAL • Critical category includes: • Surgical instruments • Cardiac and urinary catheters • Ultrasound probes used in sterile body cavities
- 23. SEMI-CRITICAL • Semi-critical items are those that come in contact with mucous membranes or non-intact skin. Semi- critical items include: • Respiratory therapy and anesthesia equipment • Endoscopes (some varieties)
- 24. NON-CRITICAL • Non-critical items are those that come in contact with intact skin but not mucous membranes. Examples of non-critical items are: • Bedpans • Blood-pressure cuffs • Crutches • Bed rail • Linens • Bedside tables
- 25. Figure 9.2 Relative susceptibilities of microbes to antimicrobial agents.
- 26. ❑ The Selection of Microbial Control Methods 2. Relative susceptibility of microorganisms ➢The most resistant microbes include the following:- 2.1 Bacterial endospores: • Endospores are considered the most resistant microbial form. • Cysts are other structures that some microorganisms can form to help protect them in harsh conditions • The endospores of Bacillus and Clostridium (Gram- positive bacteria) are the most resilient forms of life. They can survive environmental extremes of temperature, acidity, and dryness and can withstand many because they form spores.
- 27. ENDSPORES Dormant, highly resistant structures formed by vegetative bacterial cells in unfavorable environments. ▪ Two-phase life cycle: 1. Vegetative state Cell is metabolically active 2. Endospore state Dormant • Are resistant to high temperatures, most disinfectants, antibiotics, and some radiation • Survive until environmental stimuli trigger germination
- 28. Endospores re-enter vegetative growth and cell division by a complex process called germination; which is a phase triggered by some environmental triggers
- 29. ❑ The Selection of Microbial Control Methods 2. Relative susceptibility of microorganisms ➢The most resistant microbes include the following: 2.2 Species of mycobacteria: The cell walls of members of this species such as Mycobacterium tuberculosis contain a large amount of a waxy lipid. The wax allows these bacteria to survive drying and protects them from most water-based chemicals; therefore, medical personnel must use strong disinfectants or heat to treat whatever comes into contact with tuberculosis patients, including utensils, equipment, and patients’ rooms
- 30. Mycobacterium tuberculosis • Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain.
- 31. ❑ The Selection of Microbial Control Methods • Factors Affecting the Efficacy of Antimicrobial Methods 3. Environmental conditions 3.1 Temperature and pH • Affect microbial death rates: Warm disinfectants, for example, generally work better than cool ones because chemicals react faster at higher temperatures • Alter the efficacy of antimicrobial methods
- 32. ❑ The Selection of Microbial Control Methods • Factors Affecting the Efficacy of Antimicrobial Methods 3. Environmental conditions 3.2 Organic materials: Organic materials, such as fat, feces, vomit, blood, and the intercellular matrix of biofilms, interfere with the penetration of heat, chemicals, and some forms of radiation, and in some cases these materials inactivate chemical disinfectants. • For this reason, it is important to clean objects before sterilization or disinfection so that antimicrobial agents can thoroughly contact all the object’s surfaces.
- 33. ❑ Action of Antimicrobial Agents We will go through many types of chemical and physical microbial controls; however, you should remember that regardless of the chosen method, their modes of action fall into two basic categories: 1. Alteration of cell walls or cytoplasmic membrane • Cell usually wall maintains integrity of cell • Cells burst due to osmotic effects when damaged • Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cell • Cellular contents leak out when damaged • Non-enveloped viruses have greater tolerance of harsh conditions
- 34. • Why are nonenveloped viruses more resistant than enveloped viruses? Viral envelopes are not present in all viruses, but capsids are a universal feature.
- 35. • Why are nonenveloped viruses more resistant than enveloped viruses? In enveloped viruses, the envelope is a membrane composed of proteins and phospholipids that is responsible for the attachment of the virus to its target cell. Damage to the envelope by physical or chemical agents prevents viral replication. The lack of an envelope in nonenveloped viruses accounts for their greater tolerance of harsh environmental conditions, including antimicrobial agents.
- 36. ❑ Basic Principles of Microbial Control • Action of Antimicrobial Agents 2. Damage to proteins and nucleic acids • Protein function depends on 3-D shape and bonds • Extreme heat or certain chemicals damage proteins • Chemicals, radiation, and heat can alter or destroy nucleic acids • Produce fatal mutants
- 37. Methods of Microbial Control: Physical Methods
- 38. Physical Methods of Microbial Control 1. Heat-related Methods: - Moist heat method: boiling, autoclaving, and pasteurization. - Dry heat method. 2. Refrigeration and freezing. 3. Radiation
- 39. Physical Methods of Microbial Control 1. Heat-Related Methods: temperature or heat is the most used physical method. • Effects of high temperatures: • Destroy proteins • Interfere with integrity of cytoplasmic membrane and cell wall • Disrupt structure and function of nucleic acids
- 40. Physical Methods of Microbial Control • Thermal death point (TDP) • Lowest temperature at which all microbes in a particular liquid will be killed in 10 minutes • Thermal death time (TDT) • Length of time required to kill the microorganism in a particular liquid at a given temperature • Decimal reduction time (DRT) • Related to bacterial resistance • Indicates the time in which 90% of the bacterial population will be killed at a given temperature • It is referred to to measure the effectiveness of heat sterilization.
- 41. Physical Methods of Microbial Control • Heat-Related Methods A. Moist Heat Method: • Require special equipment. Used to disinfect, sanitize, sterilize, and pasteurize • Destroy proteins and destroys cytoplasmic membranes • More effective than dry heat • Methods of microbial control using moist heat: • Boiling • Autoclaving • Pasteurization
- 42. Physical Methods of Microbial Control • Heat-Related Methods A. Moist Heat Method : • Boiling: • Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses within 10 minutes at sea level. • Boiling time is critical • Different elevations require different boiling times: it is important to realize that at higher elevations, water boils at lower temperatures because atmospheric pressure is lower. • Endospores, protozoan cysts, and some viruses (such as hepatitis viruses) can survive boiling Eukaryotes are often multi-celled organisms as protozoa
- 43. Physical Methods of Microbial Control • Heat-Related Methods A. Moist Heat Method : • Boiling: • Because bacterial endospores can withstand boiling for more than 20 hours, boiling is not recommended when true sterilization is required. Boiling is effective for sanitizing restaurant tableware or disinfecting baby bottles.
- 44. Physical Methods of Microbial Control • Heat-Related Methods A. Moist Heat Method : • Autoclaving: • Pressure applied to boiling water prevents steam from escaping: Practically speaking, true sterilization using heat requires higher temperatures than that of boiling water. To achieve the required temperature, pressure is applied to boiling water to prevent the escape of heat in steam.
- 45. Physical Methods of Microbial Control • Heat-Related Methods A. Moist Heat Method : • Autoclaving: • Boiling temperature increases as pressure increases: The reason that applying pressure succeeds in achieving sterilization is that the temperature at which water boils increases as pressure increases.
- 46. Autoclave Consists of pressure chamber, pipes to supply and release the steam, and valves to remove air—control of pressure; also gauges to monitor the procedure. Usually takes 20 minutes
- 48. Physical Methods of Microbial Control • Heat-Related Methods A. Moist Heat Method : • Autoclaving: Scientists use several means to ensure that an autoclave has sterilized its contents:- ✓ A chemical (color indicator) that changes color when the proper combination of temperature and time has been reached. ✓ Using of plastic beads that melt when sterile conditions are met. ✓ A biological indicator of sterility uses endospores of bacteria such as Bacillus impregnated into tape. After autoclaving, the tape is aseptically inoculated into sterile broth. If no bacterial growth appears, the original material is considered sterile.
- 50. Physical Methods of Microbial Control • Heat-Related Methods A. Moist Heat Method : • Pasteurization • Used for milk, ice cream, yogurt, and fruit juices • Not sterilization
- 51. Physical Methods of Microbial Control • Heat-Related Methods B. Dry Heat Method • Used for materials that cannot be sterilized with moist heat: Some substances, such as powders and oils, cannot be sterilized by boiling or with steam. • Others, such as some metal objects, can be damaged by repeated exposure to steam. For such materials, sterilization can be achieved by the use of dry heat, as occurs in an oven.
- 52. Physical Methods of Microbial Control • Heat-Related Methods B. Dry Heat Method • Requires higher temperatures for longer time than moist heat because dry heat penetrates more slowly. For instance, whereas an autoclave needs about 15 minutes to sterilize an object at 121C, an oven at the same temperature requires at least 16 hours to achieve sterility. • Dry-heat methods of sterilization include: • Incineration: is ultimate means of sterilization • Use of a hot-air oven.
- 53. Incineration is the process of burning hazardous materials at temperatures high enough to destroy contaminants
- 55. Physical Methods of Microbial Control • Think about it: • Why are Bacillus endospores used as sterility indicators?
- 56. Physical Methods of Microbial Control Bacterial spores are frequently used as a biological indicator (BI) of sterility, primarily because bacterial spores exhibit elevated resistance to chemical and physical methods of sterilization
- 57. Physical Methods of Microbial Control Why is moist heat as a microbial control more effective than dry heat? Because water is a better conductor of heat than air. An example from your kitchen readily demonstrates this: you can safely stick your hand into an oven at 350 F for a few moments, but putting a hand into boiling water at the lower temperature of 212 F would burn you severely.
- 58. Physical Methods of Microbial Control 2. Refrigeration and freezing • Refrigeration: temperatures between 0°C and 7°C or freezing temperatures below 0°C. • These processes decrease microbial metabolism, growth, and reproduction because chemical reactions occur more slowly at low temperatures. • Cold temperatures are only bacteriostatic for many microbes. • Halts the growth of many pathogens. • Some pathogens named psychrophilic (cold-loving) are capable of reproduction in a refrigerated environment
- 59. Physical Methods of Microbial Control 2. Refrigeration and freezing • Microbicidal agent • Agent designed to destroy microbes • Bacteriocidal, fungicidal, virucidal • Microbiostatic • Microbial growth is at standstill • Bacteriostatic, fungistatic
- 60. Physical Methods of Microbial Control 3. Radiation • Irradiation is the sterilization process in which objects sensitive to extreme heat are exposed to radiation. • Using ionizing radiation directly or indirectly causes damage to the DNA or RNA genetic material inside a microorganism. • If the DNA or RNA is damaged, the pathogenic cell dies. Germicidal lamps that emit UV light are commonly used in the laboratory to disinfect equipment.