History and Definitions of Microbial Control

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Questions and Answers

What are two microbial characteristics that can affect the effectiveness of antimicrobial treatments?

Microbial load and presence of organic matter.

Explain how microbial control agents damage cellular proteins.

They break hydrogen bonds and covalent bonds within the proteins.

Why is moist heat sterilization considered more effective than dry heat sterilization?

Moist heat sterilization coagulates cellular proteins, making it more efficient in killing microorganisms.

What temperature range is used for dry heat sterilization and how long must the exposure last?

The temperature range is 148–260°C, and the exposure must last at least 45 minutes. Signup and view all the answers

What is the principle behind the sterilization effect of dry heat?

The principle is the oxidation of microorganisms by heat. Signup and view all the answers

Describe one physical method of microbial control that involves temperature variations.

Low heat can be used as a method for microbial control. Signup and view all the answers

What is the boiling point of water and how does it relate to microbial control?

The boiling point of water is 100°C, which is a critical temperature for the boiling method of sterilization. Signup and view all the answers

What are two methods of dry heat sterilization mentioned?

Direct flaming and incineration. Signup and view all the answers

What is the boiling point of water at a pressure of 15 psi in Celsius?

121°C Signup and view all the answers

What is the primary goal of pasteurization?

To neutralize pathogens without altering the flavor of food. Signup and view all the answers

Describe the Tyndallization method.

It involves moist heat at 100°C using free-flowing steam and is performed through 2 to 3 exposures with intervals. Signup and view all the answers

What exceptions to heat sterilization are mentioned for microbial control?

Bacterial endospores and parvovirus. Signup and view all the answers

What is a HEPA filter used for?

To remove microbes from the air. Signup and view all the answers

What temperature and duration are involved in HTST pasteurization?

At least 72°C for 15 seconds. Signup and view all the answers

What does UHT sterilization stand for and what are its parameters?

Ultra High Temperature; at least 135°C for 2-5 seconds. Signup and view all the answers

Explain the process of inspissation in low temperature sterilization.

It is a fractional method of sterilization at 60°C in an oven, alternating with intervals for 2 to 3 days. Signup and view all the answers

Who proposed the early notion of germ theory and how did he believe microbes were transferred?

Girolamo Fracastoro proposed that seed-like 'spores' could be transferred through direct contact, contaminated clothing, or the air. Signup and view all the answers

What practice did Ignaz Semmelweis promote to prevent disease during childbirth?

Semmelweis promoted handwashing before medical procedures. Signup and view all the answers

What is the significance of John Snow's work in the history of microbial control?

John Snow conducted studies that traced cholera outbreaks, demonstrating the importance of epidemiology in public health. Signup and view all the answers

What surgical advancement is associated with Joseph Lister?

Joseph Lister introduced aseptic surgery, emphasizing handwashing and the use of carbolic acid as an antiseptic. Signup and view all the answers

What process did Louis Pasteur develop to kill spoilage microorganisms?

Pasteur developed the process known as pasteurization. Signup and view all the answers

What was Robert Koch's major contribution to microbiology?

Robert Koch was the first to identify the link between a specific microbe and a known disease. Signup and view all the answers

Who is credited with the development of the first vaccine against smallpox?

Edward Jenner is credited with commercializing the first vaccine against smallpox using cowpox scabs. Signup and view all the answers

What does sterilization refer to in microbial control?

Sterilization refers to the removal or destruction of all living microorganisms. Signup and view all the answers

What is the difference between disinfection and antisepsis?

Disinfection is the destruction of vegetative pathogens on inanimate objects, while antisepsis refers to the destruction of pathogens on living tissue. Signup and view all the answers

What does the term 'degerming' mean?

Degerming refers to the removal of microbes from a limited area, such as skin around an injection site. Signup and view all the answers

How do microorganisms behave at refrigeration temperatures?

Microorganisms do not reproduce at ordinary refrigerator temperatures (0–7°C) but many can survive without growing. Signup and view all the answers

What is High Pressure Processing (HPP) and what is its primary benefit?

HPP is a non-thermal food preservation technique that kills microorganisms while preserving taste, texture, and nutritional value. Signup and view all the answers

What happens to microorganisms during desiccation?

Microorganisms lose water and cannot grow, though some can remain viable. Signup and view all the answers

Describe the effect of high osmotic pressure on microorganisms.

High salt concentrations cause microbial plasmolysis, affecting their ability to grow. Signup and view all the answers

What is the role of ultraviolet (UV) radiation in controlling microorganisms?

UV radiation reduces airborne contamination but has poor penetration and its effectiveness relies on exposure time and intensity. Signup and view all the answers

How does ionizing radiation sterilize materials?

Ionizing radiation removes electrons from atoms, creating free radicals that can damage living cells. Signup and view all the answers

What is the primary effect of ionization of water due to radiation?

The ionization of water produces highly reactive free radicals. Signup and view all the answers

Why are bacterial endospores significant in the context of microbial control?

Bacterial endospores resist desiccation and can survive harsh conditions, making them challenging to eliminate. Signup and view all the answers

What is the primary way alcohols act as disinfectants?

Alcohols denature proteins and dissolve lipids. Signup and view all the answers

Explain how hypochlorous acid is formed and its use in disinfection.

Hypochlorous acid is formed when chlorine is added to water and is used as a disinfectant. Signup and view all the answers

Describe the oligodynamic action of heavy metals in microbial control.

Heavy metals exert antimicrobial action through oligodynamic action, which is the ability of small amounts of metals to kill microorganisms. Signup and view all the answers

What is the function of surface-active agents, and give an example?

Surface-active agents decrease surface tension and assist in the removal of microorganisms; an example is soap. Signup and view all the answers

What is a characteristic feature of quaternary ammonium compounds (quats) in antimicrobial action?

Quats disrupt plasma membranes, allowing cytoplasmic contents to leak out. Signup and view all the answers

How do organic acids like sorbic and benzoic acid function in food preservation?

Organic acids inhibit fungal metabolism, thus preventing spoilage. Signup and view all the answers

What is the role of aldehydes such as formaldehyde in microbial control?

Aldehydes inactivate proteins, which leads to their antimicrobial effect. Signup and view all the answers

Describe how ethylene oxide functions as a gaseous chemosterilizer.

Ethylene oxide works by penetrating materials and killing microorganisms through protein denaturation. Signup and view all the answers

Study Notes

History of Microbial control

Microbial control dates back to the 1500s when Girolamo Fracastoro proposed that "spores" transferred diseases.
Ignaz Semmelweis promoted handwashing in medical procedures to prevent puerperal fever.
John Snow studied cholera outbreaks and traced their sources.
Joseph Lister introduced aseptic surgery practices and used carbolic acid as an antiseptic.
Louis Pasteur and Robert Koch contributed significantly to the "Golden Age of Microbiology".

Microbial Control: Definitions

Sterilization: eliminates all living microorganisms.
Commercial Sterilization: targets Clostridium botulinum endospores in canned food.
Sanitization: reduces microbial counts to safe levels for public health.
Disinfection: eliminates vegetative pathogens on inanimate objects.
Antisepsis: eliminates vegetative pathogens on living tissue.

Microbial Control: Actions of Agents

Alteration of Membrane Permeability: Microbial control agents can disrupt cell membranes, causing leakage.
Damage to Proteins and Nucleic Acids: Agents can damage or disrupt protein structure or interfere with DNA/RNA synthesis.

Physical Methods of Microbial Control

Heat: One of the most common methods of microbial control.
- Dry Heat Sterilization: Uses high temperatures (148–260°C) for at least 45 minutes to kill spores and vegetative forms. Examples include direct flaming and incineration.
- Moist Heat Sterilization: More effective than dry heat due to the ability of water to penetrate cells.
  - Boiling: Kills vegetative pathogens, some viruses, and spores within 10 minutes at 100°C.
  - Autoclave: Uses steam under pressure (15 psi) to reach 121°C and kill even endospores in 15-30 minutes.
  - Pasteurization: Uses high temperatures for short durations to eliminate pathogens without affecting food flavor. Two types: HTST (72°C for 15 seconds) and UHT (135°C for 2-5 seconds).
  - Fractional Sterilization: Uses moist heat at 100°C, repeatedly over several days, for vegetative forms and endospores.
    - Tyndallization: Uses free-flowing steam.
    - Inspissation: Uses an oven at 60°C.
Filtration: Passes liquid or gas through a filter with pores small enough to retain microbes.
- HEPA Filters: Remove microbes from air.
- Membrane Filters: Made of nitrocellulose or cellulose acetate, can filter out bacteria, viruses, and large proteins.
Low Temperature: Slows microbial growth but may not kill them.
- Refrigeration (0-7°C) inhibits growth.
- Freezing (subzero temperatures) preserves microbes but doesn't necessarily kill them.
High Pressure: A non-thermal food preservation technique that kills microorganisms by using high pressure for a set period.
- HPP (High Pressure Processing) preserves taste, texture, and nutrients.
Desiccation: Drying out removes water, inhibiting microbial growth.
- Viruses, bacterial endospores, and protozoal cysts can survive desiccation.
Osmotic Pressure: High salt or sugar concentrations cause plasmolysis, inhibiting growth.
- Molds and yeasts tolerate low moisture/high osmotic pressure better than bacteria.
Radiation: Energy that can damage cells.
- Ultraviolet (UV) Radiation: Used to reduce airborne contamination. Effectiveness depends on exposure time, intensity, and microbial susceptibility. Has poor penetration.
- Ionizing Radiation: High energy radiation (gamma rays, beta rays) removes electrons from molecules, killing microorganisms.

Chemical Methods of Microbial control

Disinfectants: Kill microorganisms on inanimate objects.
- Phenol and Phenolics: Disrupt cell membranes and denature proteins.
- Halogens: Oxidize cellular components.
  - Chlorine: Used as a disinfectant in gaseous form (CI2) or compounds.
  - Iodine: Available as a tincture or iodophor.
- Alcohols: Denature proteins and dissolve lipids.
  - Ethanol (60-90%) and Isopropanol are effective.
- Heavy Metals and Compounds: Exert oligodynamic action (inhibiting microbial growth in small amounts).
  - Silver, mercury, copper, and zinc are common examples.
- Surface-Active Agents: Decrease surface tension, aiding in removing microbes.
  - Soaps have limited germicidal activity but help remove microbes.
  - Acid-anionic detergents are used for cleaning dairy equipment.
- Quaternary Ammonium Compounds (Quats): Cationic detergents that disrupt cell membranes. More effective against gram-positive bacteria.
  - benzalkonium chloride
  - cetylpyridinium chloride
- Organic Acids and Derivatives: Inhibit fungal metabolism. Used as food preservatives.
  - Sorbic acid, benzoic acid, and propionic acid.
- Aldehydes: Inactivate proteins. Among the most effective chemical disinfectants.
  - Formaldehyde and glutaraldehyde.
- Gaseous Chemosterilizers: Penetrate materials and kill all microorganisms.
  - Ethylene oxide is most commonly used.

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Description

Explore the significant milestones in microbial control from the 1500s to modern practices. Learn about key figures like Girolamo Fracastoro, Ignaz Semmelweis, and Louis Pasteur, as well as essential definitions like sterilization and disinfection. This quiz will test your knowledge on the history and methods used in controlling microbial growth.