micro lecture 1&2 midterm

• Microbial Control


  Control of microbial growth means to inhibit or prevent growth of microorganisms. This control is effected in two basic ways: by killing microorganisms or by inhibiting the growth of microorganisms
• Why we need to control microbes

  • Prevent diseases
  • Preserve food and increase shelf-life
  • Quality control during production and research
• Joseph Lister & Ignaz Semmelweis


  • Antiseptic methods for surgery, boiling of surgical instruments
  • Disinfectants for hands and wounds
• Florence Nightingale


  • Sanitary procedures and training
  • Procedures for reducing hospital overcrowding
• Sterilization


  The removal or destruction of all microbes, including viruses and bacterial endospores, in or on an object or habitat
• Aseptic


  An environment or procedure that is free of contamination by pathogens
• Disinfection


  The killing, inhibition, or removal of microorganisms that may cause disease. The primary goal is to destroy potential pathogens
• Degerming


  The removal of microbes from a surface by scrubbing
• Sanitization


  The process of disinfecting places and utensils used by the public to reduce the number of pathogenic microbes to meet accepted public health standards
• Pasteurization


  The use of heat to kill pathogens and reduce the number of spoilage microorganisms in food and beverages
• Microbial death


  The permanent loss of reproductive ability under ideal environmental conditions
• Microbial death rate


  Used to evaluate the efficacy of an antimicrobial agent. Usually constant over time for any particular microorganism under a particular set of conditions
• Modes of Action of Antimicrobial Agents

  1. Alteration of cell walls (fungi)

  2. Alteration of cell membranes (virus)
• Factors Affecting the Efficacy of Antimicrobial Methods

  • Site to be Treated
  • Degree of Resistance of Microorganisms
  • Environmental Conditions (Temperature, pH)
• Phenol Coefficient


  The first method used. If >1.0, the agent is more effective than phenol. The larger the ratio, the greater the effectiveness
• Disk-diffusion Method


  The current standard test. The most effective agent is the one that entirely prevents microbial growth at the highest dilution
• In-use Test


  A more realistic method. Swabs are taken from actual objects before and after application of disinfectant. More accurate determination of a given disinfection agent for each specific situation
• Physical Methods

  • Heat
  • Cold
  • Desiccation
  • Radiation
  • Ultrasonic Waves
  • Filtration
  • Gaseous Atmosphere
• Chemical Methods

  • Disinfectants
  • Antiseptics
  • Preservatives
• Thermal death point


  Lowest temperature that kills all cells in a broth in 10 minutes
• Thermal death time


  The time it takes to completely sterilize a particular volume of liquid at a set temperature
• Decimal reduction time (D)


  Time required to destroy 90% of the microbes in a sample
• Moist Heat


  To disinfect, sanitize, sterilize and pasteurize by denaturing proteins and destroying cytoplasmic membranes. More effective than dry heat because water is better conductor than air
• Dry Heat


  Denatures proteins and fosters the oxidation of metabolic and structural chemicals. For substances cannot be sterilized by boiling or steam or materials can be damaged by repeated exposure to steam
• Boiling


  Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses
• Autoclaving


  Pressure applied to boiling water prevents steam from escaping. Increases boiling temp and pressure
• Pasteurization


  Heating foods to kill pathogens and control spoilage without altering the quality of foods. Can be achieved by batch sterilization, flash sterilization, or ultra high temp sterilization
• Refrigeration


  Temperature between 0°C - 7°C. Decreases microbial metabolism, growth and reproduction
• Freezing


  Temperature below 0°C. Decreases microbial metabolism, growth and reproduction
• Desiccation


  Inhibits microbial growth because of the absence of water
• Lyophilization


  A technique combining freezing and drying to preserve microbes and cells
• Filtration


  The passage of a fluid (liquid or gas) through a sieve to trap and separate particles (cells or viruses) from the fluid
• Osmotic Pressure


  The pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
• Types of Solutions

  • Isotonic
  • Hypertonic
  • Hypotonic
• Radiation


  • Particulate radiation
  • Electromagnetic radiation
• Ionizing Radiation


  Wavelengths shorter than 1 nm. Electron beams, gamma rays, and x-rays
• Non-ionizing Radiation


  Wavelength greater than 1 nm. UV light, visible light, infrared radiation and radio waves
• Phenols and Phenolics


  Compounds derived from phenol molecules that have been chemically modified by the addition of halogens or organic functional groups. Commonly used in health care settings, laboratories and households
• Alcohols


  Commonly used are isopropanol and ethanol. Denature proteins and disrupt cytoplasmic membranes
• Oxidizing Agents


  Used by health care workers to kill anaerobes in deep puncture wounds