Microbial Control and Sterilization Techniques

Posted on Dec 19, 2024 in Biology

Sterilization and Microbial Control

Sterilization – a process that destroys or removes all viable microorganisms, including viruses.

Sterile – any material that has been subjected to sterilization.

Bactericide – chemical that destroys bacteria except for those in the endospore stage.

Fungicide – chemical that can kill fungal spores, hyphae, and yeasts.

Virucide – chemical known to inactivate viruses, especially on living tissues.

Sporicidal agent – destroys bacterial endospores.

Microbistasis – microbes are temporarily prevented from multiplying but are not killed outright.

  1. Bacteriostatic agent – prevents the growth of bacteria on tissues or on objects in the environment.
  2. Fungistatic chemical – inhibits fungal growth.

Germicide – also called a microbicide; any chemical agent that kills pathogenic microorganisms.

Disinfection – use of a physical process or a chemical agent to destroy vegetative pathogens but not bacterial endospores.

Sepsis – the growth of microorganisms in the blood and other tissues.

Asepsis – any practice that blocks the entry of infectious agents into sterile tissues and thus prevents infection.

Antisepsis – prevention of infection of superficial tissues by the topical application of chemical agents.

Antiseptics – chemical agents applied directly to exposed body surfaces (skin and mucous membrane), wounds, and surgical incisions.

Sanitization – any cleansing technique that removes debris, soil, microorganisms, and toxins.

Degermation – reduction in microbial load within living tissues through mechanical means (e.g., scrubbing the skin).

Microbial Death – the permanent loss of reproductive capacity of microbes even under optimal growth conditions.

Factors Affecting Microbial Death

  1. Cell wall – chemical agents block its synthesis, digest it, or break down its surface.
  2. Cell membrane – the cell loses its selective permeability and can neither prevent the loss of vital molecules nor bar the entry of damaging chemicals.
    1. Surfactants – microbicidal agents that lower the surface tension of cell membranes.
    2. Alcohol – dissolves membrane lipids and strips membranes away from cells.
  3. Protein and Nucleic Acid Synthesis – any chemical that blocks the synthesis of protein can affect the cell’s function and survival.
  4. Protein Function – antimicrobials have the capacity to disrupt the structure of proteins, also called denaturation.
    1. Denaturation – occurs when the bonds that maintain the secondary and tertiary structure of protein are broken.
    2. Coagulation – irreversible solidification of egg white when cooked.
    3. Alcohols and acids – coagulate proteins.

Temperature and Microbial Control

Microbicidal – temperatures that exceed the maximum growth temperature.

Microbistatic – temperatures below the minimum growth temperature.

Physical States of Heat Used in Microbial Control

  1. Moist heat – occurs in the form of hot water, boiling water, or steam (vaporized water).
  2. Dry heat – denotes air with a low moisture content that has been heated by a flame or electric heating coil.

Incinerator – alternative to Bunsen burner; safer and prevents splatter of the inoculum.

Radiation in Microbial Control

Radiation – energy emitted from atomic activities and dispersed at high velocity through matter or space.

Types of Radiation Suitable for Microbial Control

  1. Gamma rays (ionizing radiation)
  2. X-rays (ionizing radiation)
  3. UV radiation (nonionizing radiation)

Filtration – fluid is strained through a filter with openings large enough for the fluid to pass through but too small for microorganisms to pass through.

Germicide Levels

  1. High-level germicides – can kill endospores; can be used as sterilants if properly used; used in medical devices.
  2. Intermediate-level germicides – can kill fungal (but not bacterial) spores, resistant pathogens, and viruses.
  3. Low-level germicides – can eliminate only vegetative bacteria, vegetative fungal cells, and some viruses.

Metabolism and Cellular Classification

Metabolism – all chemical workings of cells; any activity or behavior of an organism.

General Categories

  1. Catabolism – larger molecules are degraded or broken down into smaller molecules, usually with the release of energy.
  2. Anabolism – larger molecules are built from smaller ones, which results in the formation of cell structures.

Classification by Carbon Source

  1. Autotrophs – organisms that convert inorganic carbon dioxide into organic carbon.
  2. Heterotrophs – rely on more complex organic compounds as nutrients.

Classification by Energy Source

  1. Phototrophs – organisms that get their energy for electron transfer from light.
  2. Chemotrophs – organisms that obtain energy for electron transfer by breaking chemical bonds.

Virions – single virus particles; very small (~20-250 nm).

Enzyme Classes

  1. Oxidoreductase – transfer electrons from one substrate to another.
  2. Dehydrogenase – transfer a hydrogen from one compound to another.
  3. Transferase – transfer functional groups from one substrate to another.
  4. Hydrolase – cleave bonds on molecules with the addition of water.
  5. Lyase – add groups to or remove groups from double-bonded substrate.
  6. Isomerase – change a substrate into its isomeric form.
  7. Synthase – catalyze the formation of large molecules.

Virus Structure and Classification

Envelope – additional membranous layer that surrounds the nucleocapsid.

  1. Enveloped – unstable outside of the human body, and are typically transmitted by transfer of fluid.
  2. Nonenveloped – much more stable, and many can be transmitted by other mechanisms.

Peplomeres – viral proteins that modify the envelope.

Virus Types

  1. dsDNA – double-stranded DNA
  2. ssDNA – single-stranded DNA
  3. dsRNA – double-stranded RNA
  4. ssRNA – single-stranded RNA
    1. +ssRNA – positive sense; can transcribe message like mRNA.
    2. -ssRNA – negative-sense; complementary to mRNA.

Viruses usually enter the body through the mucous membranes, the inner lining of some organs and body cavities (e.g., eyes, nose, mouth, penis, vagina, and anus). Some viruses get in through a break in the skin or from a bite from a mosquito or tick.

Capsid – protein coat surrounding the nucleic acid.

Capsomeres – smaller protein components that make up the capsid.

Nucleocapsid – capsid + genome.

  1. Helical virus – have an elongate tube-like structure, with the capsomeres arranged helically around the coiled genome.
  2. Icosahedral virus – have a spherical shape, with icosahedral symmetry consisting of 20 triangular faces.
    1. Adenovirus – nonenveloped animal virus.
  3. Complex virus – unusual in design or components.