Micropara FINALS

• Scientific control of microbial growth began only about 100 years ago
• Pioneers of scientific control of microbial growth

  • Louis Pasteur
  • Ignaz Semmelweis
  • Joseph Lister

  
• Techniques of aseptic surgery


  Prevent microbial contamination of surgical wounds
• Sterilization


  Removal or destruction of all living microorganisms
• Heating


  • Most common method of sterilization
• Sterilant


  A sterilizing agent
• Filtration


  Used in sterilizing liquids or gases
• Any material that has been subjected to the sterilization process is said to be sterile
• Commercial sterilization


  Limited heat treatment (e.g. canning) that does not kill all microorganisms, especially thermophiles
• Disinfection


  Destroying harmful microorganisms, usually the destruction of vegetative (non–endospore-forming) pathogens
• Antisepsis


  When disinfection treatment is directed at living tissue (e.g. use of antiseptic)
• Degerming or degermation


  Mechanical removal of most of the microbes in a limited area (e.g. swabbing skin with alcohol before injection)
• Sanitization


  Lowering microbial counts to safe public health levels and minimize the chances of disease transmission from one user to another (e.g. in glass and table wares)
• Sepsis


  Bacterial contamination, as in septic tanks for sewage treatment
• Aseptic


  The absence of significant contamination, important in surgery to minimize contamination
• Biocide, germicide, fungicide, virucide


  Treatments that cause the outright death of microbes
• Bacteriostasis


  Treatments that inhibit the growth and multiplication of bacteria
• When bacterial populations are heated or treated with antimicrobial chemicals, they usually die at a constant rate
• Factors that influence the effectiveness of antimicrobial treatments

  • Number of microorganisms
  • Nature of the microorganisms in the population
  • Temperature and pH of the environment
  • Concentration (dosage, intensity) of the agent
  • Mode of action of the agent
  • Presence of solvents, interfering organic matter, and inhibitors

  
• Antibiotics


  May either be bactericidal or bacteriostatic
• Damages the cell wall


  1. By blocking its synthesis, digesting it, or breaking down its surface

  2. A cell deprived of a functioning cell wall becomes fragile and is lysed very easily
• Agents that damage the cell wall


  • Some antimicrobial drugs (penicillins)
  • Detergents and alcohol
• Alteration of membrane permeability


  Damage causes cellular contents to leak into the surrounding medium
• Damage to proteins and nucleic acids


  1. Breakage of bonds that form enzymes results in denaturation of the protein

  2. Cell can no longer replicate, nor can it carry out normal metabolic functions such as the synthesis of enzymes when nucleic acids are damaged
• Development of resistance to antimicrobial drugs by target microbes is a worldwide public health problem
• Persister cells


  Term adopted for bacteria that are highly susceptible to antimicrobials when first exposed, but then develop resistance
• Cardinal temperature


  Range of temperature for the growth of a microbe

  
• Optimum temperature


  Temperature that promotes the fastest growth and metabolism, intermediate between the minimum and maximum
• Microbiostatic


  Temperatures below the minimum temperature for growth
• Psychrophiles


  Microbes with optimum growth below 15°C, capable of growth at 0°C, rarely pathogenic
• Psychrotrophs


  Microbes that grow slowly in cold but grow fastest between 15°C- 30°C, including Staphylococcus aureus and Listeria monocytogenes

  
• Microbicidal


  Temperatures that exceed the maximum temperature for growth, effects are not reversible and most microbes will be destroyed
• Thermoduric


  Microbes that can survive short exposure to high temperatures but are normally mesophiles, common contaminants of heated/pasteurized foods
• Moist heat

  Hot water, boiling water, or steam, damages cellular structures, coagulation and denaturation of proteins, operates at lower temperatures and shorter exposure times

  
• Dry heat


  Air with low moisture content, dehydrates the cell and alters protein structure, needs higher temperatures

  
• Bacterial endospores exhibit the greatest resistance to heat, vegetative states are least resistant</b>

  
• Sterilization with steam under pressure


  Increases the temperature of steam by exposing it to increased pressure, not the pressure itself that kills microbes
• Nonpressurized steam


  Exposes items to free-flowing steam for 30 to 60 minutes, temperature never gets above 100°C so highly resistant spores could survive

  
• Boiling water


  Disinfection method, exposing materials to boiling water for 30 minutes kills most non-spore-forming pathogens
• Pasteurization


  Applying heat to consumable liquids to kill potential agents of infection and spoilage, while retaining the liquid's flavor and food value