Lecture 6: Control of Cell Growth

Prevention of Hospital-Acquired Infections

  • Methods for prevention: Focus on controlling the growth of microbes

Controlling Microbial Growth

  • Sterilization: A treatment that destroys all microbial life

  • Disinfection: reduces the number of pathogens

    • Types of Disinfection:

      • Disinfectants: Applied to inanimate surfaces (e.g., tables).

      • Antiseptics: Applied to living tissues (e.g., iodine on skin).

  • Microbicidal: kill microbes.

    • Examples include:

      • Bactericidal: Kills bacteria.

      • Virucidal: Kills viruses.

      • Fungicidal: Kills fungi.

  • Microbiostatic: stop growth of microbes.

Methods for Controlling Microbial Growth

Physical Methods

  • Heat: altering membrane and denaturing proteins

    • works through denaturing proteins, and altering membranes

    • penetrates to reach microbes through the material

      • reaches all microbes present

    • only good for heat-stable materials

    • example: flame and boiling

    • Dry Heat methods:

      • incineration

      • oven

      • flame

    • Moist Heat Methods:

      • autoclave: uses heat and pressure combo

        • Typical Settings: 121°C for 15 minutes at 15 psi.

        • destroys endospores

        • preferred method for sterilization for lab, surgical and medical equipment

      • boiling

        • Boiling is effective but doesn't achieve sterilization.

      • pasteurization: heats liquids but doesn’t boil them

        • reduces number of microbes present

  • Filtration: A method used to filter liquids or air by removing microbes through small filter pores.

    • Example:

      • Liquid filtration device utilizing a vacuum (membrane filters)

      • air filters (HEPA filters)

      • membrane filters

  • Radiation (Irradiation): Damages DNA and other molecules

    • Examples:

      • Ionizing Radiation (gamma rays and x-rays): Breaks DNA bonds

        • causes single or double stranded breaks in DNA backbone

      • Non-ionizing Radiation (UV Light): Related to natural sunlight, can cause DNA damage.

        • adds thymine dimer, where thymine become covalently linked

          • causes frameshift or point mutation

Chemical Methods

  • Chemical Methods:

    • dissolve membranes

    • destroy proteins and other molecules

    • Types of Chemical Methods:

      • Surfactants: soap

        • interact with and emulsify lipids, dats, and oils so they ware washed away by water

          • have both hydrophilic and hydrophobic properties, aiding in washing away microbes.

            • hydrophilic end interact with water

            • hydrophobic end interacts with microbes

      • Alcohols: ethyl alcohol (in hand sanitizers), isopropyl alcohol (rubbing alcohol)

        • damage microbial membranes and denature proteins.

      • Peroxygens: hydrogen peroxide

        • produce free radicals that damage macromolecules

          • free radicals: unpaired electrons

            • very reactive

              • leads to cellular damage and killing microbes

      • Halogens: bleach and iodine

        • oxidizes macromolecules, stealing electrons from microbial molecules to kill them.

      • Alkylating Agents: ethylene oxide

        • replaces hydrogen with an alkyl group

          • alkyl group: carbon and hydrogen

        • destroying molecule, including DNA

        • enters crevices, small enough to even penetrate pores of plastic

        • works at low temperature

          • good for plastic