Physical and Chemical ControlThis is a featured page

Physical and Chemical Agents for Microbial Control
Some questions to ponder:
  • What is sterilization, and when is it desirous?
  • When is sterilization not needed?
  • What products/techniques can be used to achieve sterilization? When would you use one instead of another?
  • Why are vegetative (actively growing) microbes easier to kill than spores?
  • Be familiar with the various definitions
  • How do the various chemical agents work? Know examples within each category. Why would you choose one product over another?
  • How does non-ionizing radiation differ from ionizing radiation? What applications are there for each?
  • How about adding a few things to this list yourselves? Perhaps a lot of "how" and "why" questions, such as "how does UV light affect microbes?" or "why is betadine used instead of pure iodine?"

Some definitions:
  • Sterilization is a method used to destroy all microorganisms and viruses. The most widely used method of sterilization is heat. Chemicals called sterilants can be used, but there are only a few chemicals that can fully destroy microorganisms and viruses. Sterilization is only for inanimate objects because the human body cannot withstand the heat or chemicals used to sterilize. The objects are either sterile or unsterile. They can not be partially sterile.
  • Germicides are any chemical agent that is able to kill pathogenic microorganisms. These can be used on any living or non-living object but usually will not kill any of the resistant microbial cells. A disinfectant is a physical process or a chemical that is used to kill vegetative pathogens but they do not have any effect on bacterial endo spores. Disinfectants are not used on humans. They are only for inanimate objects because they could be toxic to humans.
  • Sepsis is the systemic response to an infection that can cause organ failure and maybe even death. It is the growth of microorganisms in the body or having toxins present in the blood or other bodily tissues. Asepsis is the practice to reduce or eliminate contamination from bacteria, viruses, and parasites from getting into a sterile environment to prevent the chance of infections. Commonly used in the health care setting. Sanitation is a cleaning technique that removes microorganisms to a safe level. A type of sanitizer is soap or a detergent. Because something is sanitary does not mean it is completely free of microorganisms, it means that the object is safe to use.
  • Degermation is a process where you scrub the skin or soak the skin in chemicals.
  • Disinfection is a process used to destroy vegetative pathogens, but not endospores. Disinfectants are able to kill pathogens on contact. Usually on inanimate objects
  • Surfactant There are two types of surfactants. They are soap and detergents. It works by lowering the surface tension which causes the membrane to rupture. This allows the two substances to mix together. Surfactant is known to be amphipathic, which means it has both hydrophobic and hydrophilic groups. Here is a video just for fun to see how it works.
  • Microbial death Microbial death is where there is a permanent loss of reproductive ability. When put in optimum growth conditions the microorganisms will not grow. Knowing if a microorganism is dead is hard because it is impossible to detect any vital signs. Loss of movement is not a good indicator of death either.
Q: Which of the following terms is defined as the destruction of vegetative pathogens but not bacterial endospores?
a. disinfection
b. antisepsis
c. sterilization
A: disinfection

Q: What is the goal of sterilization?
a. the destruction to protozoal trophozoites
b. the destruction of bacterial endospores
c. the destruction or inhibition of vegatative pathogens through chemicals applied to body surfaces
A: the destruction of bacterial endospores

Factors Influencing The Death Rate of Microorganisms
~The permanent loss of reproductive capatability, even under optimum growth conditions~
  1. Length of exposure to a physical or chemical agent
  2. Effect of the microbial load
  3. Resistance of spores
  4. Action of the agent

Factors That Influence Action of Microbial Agents
  1. How many microbes there are
  2. What types of microorganisms they are
  3. The temp and pH of the environment
  4. Dose and intensity of the disinfectant
  5. The way in which the agent is able to kill the microorganism
  6. If there are solvents, inhibitors, or interfering organic matter like blood, saliva, or feces.
  7. Biofilms

Methods of Physical Control
1. Heat 2. Cold Temp 3. Desiccation 4. Radiation 5. Filtration

HEAT
  • Thermal death point TDP- the lowest temperature required to kill all microbes in a sample in 10 minutes.
  • Thermal death time TDT- the shortest length of time required to kill all test microbes at a specified temperature.
Moist Heat- use of hot water or steam
  • steam under pressure non-pressurized
  • boiling waterboiling water
  • pasteurization
Dry Heat- using heat higher than moist heat. Dry heat dehydrates the cell, removing the water necessary for metabolic reactions, and it also denatures proteins. At very high temperatures, dry heat of course oxidizes cells, reducing them to ashes. This is the method used in the laboratory when a loop is flamed or in industry when medical waste is incinerated.

COLD- The principal benefit of cold treatment is to slow growth of cultures and microbes in food during processing and storage.
  • Microbiostatic- slows the growth of microbes
  • Used to preserve food, media, and cultures
DESSICATION- To dry at normal environmental temperatures.
  • lyophilization- to dissolve; freeze drying
  • Gradual removal of water from cells, leads to metabolic inhibition
  • Not effective microbial control-many cells retain ability to grow when water is reintroduced.
RADIATION- energy emitted from atomic activities and dispersed at high velocity through matter or space.
Ionizing radiation- Gamma rays (very powerful); Radiant energy consisting of short-wave electromagnetic rays or high speed electrons that cause dislodgement of electrons on target molecules and create ions. (one of the most sensitive targets for ionizing radiation is DNA) Used to sterilize medical supplies and food products. Non-ionizing radiation- Ultraviolet light (little penetrating power); Method of microbial control, best exemplified by ultraviolet light, that causes the formation of abnormal bonds within the DNA of microbes, increasing the rate of mutation. The primary limitation of non-ionizing radiation is its inability to penetrate beyond the surface of an object. UV light thymine pyrimidines, which interfere with replication.
FILTRATION- Physical removal of microbes through a filter.
  • used to sterilize heat sensitive liquids and air in hospital isolation units.

How sand filtration works



Chemical Agents in Microbial Control
HALOGENS- A group of related chemicals with antimicrobial applications (fluorine, bromine, chlorine, and iodine)

Chlorine Compounds-chlorine- hypochlorites, chloramines; can be sporicidal
Iodine Compounds-Iodine- gentler than chlorine; idophores (betadine); can be sporicidal
PHENOLICS- Disrupts cells membranes and precipitating proteins; bacterial, fungicidal, virucidal; Not sporicidal.
  • Lysol
  • Triclosan
Joseph Lister made phenols historically significant in the world of microbiology.
CHLORHEXIDINE- Hibiclens, Hibitane; A surfactant and protein denaturant with broad microbicidal properties. Not sporicidal.
Peridex- mouthwash for gingivitis
ALCOHOLS- colorless hydrocarbons with one or more--OH functional groups. Act as a surfactant, dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi. Not sporicidal.
You can sniff alcohol pads to prevent vomiting.
HYDROGEN PEROXIDE- a colorless, caustic liquid that decomposes in the presence of light, metals, or catalase into water and oxygen gas. Creates free radicals that damage proteins and DNA. Strong solutions are sporicidal.
DETERGENTS & SOAPS- Quaternary ammonia compounds that act as surfactants that alter membrane permeability of some bacteria and fungi. Not sporicidal
Soaps mechanically remove soil and grease contaminating microbes by attaching to each other.
HEAVY METALS-Solutions of silver and mercury kill vegetative cells in low concentrations by inactivating proteins. Not sporicidal
  1. metals are very toxic to humans if ingested, inhaled, or absorbed through the skin, even in small quantities, for the same reasons that they are toxic to microbial cells
  2. the commonly cause allergic reactions
  3. large quantities of biological fluids and wastes nuetralize their actions
  4. microbes can develop resistance to metals
Oligodynamic action- toxic effect of heavy metals on microbes; exact mechanisms not fully understood but enzyme deactivation involved. Colloid particles are very small
Overuse of silver can cause argyria, a condition that permanently discolors the skin, but many people promote the use of colloidal silver, as seen in these testimonials.
Chapter 11 - MicrobiowikiChapter 11 - Microbiowiki





blue man

Here is Paul Karason, the blue man. He has been treating his dermatitis with colloidal silver, he would drink it and also rub it on his face. In doing so, he now has a condition known as Argyria, the blue-grayish man.


ALDEHYDES- Glutarahydehyde and formaldehyde kill by alkynlating protein and DNA.
Glutaraldehyde in 2% solution (CIDEX) used as sterilant for heat sensitive instruments.
Formaldehyde is a disinfectant, preservative, and toxicity limits use.
GASES AND AEROSOLS- Ethylene Oxide- steralizes


Resistance of Microbial Forms

  • Highest resistance
    • Bacterial endospores
  • Moderate resistance
    • Protozoan cysts; some fungal sexual spores (zygospores); some viruses. In general naked viruses are more resistant then enveloped forms.
  • Least resistance
    • Most bacterial vegetative cells; (other then zygospores) fungal spores and hyphae; enveloped viruses; yeasts; and protozoan trophozoites.
Mode of Action for Dry Heat
Dry heat dehydrates the cell, removing the water necessary for metabolic reactions, and it also denatures proteins. At very high temperatures, dry heat of course oxidizes cells, reducing them to ashes. This is the method used in the laboratory when a loop is flamed or in industry when medical waste is incinerated.

Q: Microbial death is defined as which of the following?
a. the permenant termination of an organisms vital processes.
b. the permenant loss of reproductive capability, even under optimal growth conditions.
c. the loss of movement in motile microbe.
A: the permenant loss of reporductive capability, even under optimal growth conditions.

QUALITIES OF CHEMICAL AGENTS USED IN HEALTH CARE
Agent Target Microbes Level of Activity Toxicity Comments
Iodine Sporicidal (slowly) Intermediate Can irritate tissure; toxic if ingested Iodophors* are milder forms
Phenolics Some bacteria, viruses, fungi Low to intermediate can be absorbed by skin; can cause CNS damage Poor solubility; expensive
Chlorhexidine * Most bacteria, some viruses, fungi Low to intermediate Low toxicity Fast-acting, mild, has residual effects
Alcohols Most bacteria, viruses, fungi Intermediate Toxic if ingested; a mild irritant; dries skin


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