Microbial Control and Destruction

• Microbial control - it is essential in order to prevent the unwanted microbial contamination, transmission of diseases and infection, stop decomposition and spoilage of food.
• The effects of microorganisms can often be controlled by simply limiting or inhibiting growth.
• Microorganisms are controlled by means of physical agents and chemical agents.
• Sterilization – the removal or destruction of all living microorganisms. It is one of the example of physical agent. It is the killing or removal of all microorganisms (including viruses)
• Decontamination – the treatment of an object or surface to make it safe to handle. As a result, it needs wiping off to remove fragments before using.
• Sepsis refers to the presence of pathogens in blood or tissues
• Disinfection – a process that directly targets pathogens although it may not eliminate all microorganisms. It requires agents called disinfectants that actually kill microorganisms or severely inhibit their growth
• Antisepsis is the prevention of infection
• Microbial control means to kill or to inhibit the growth of microorganisms
• Heating is the most common method used for killing microbes, including the most resistant forms, such as endospores. Liquids or gases can be sterilized by filtration.
• asepsis means the absence of pathogens
• Decimal Reduction Time is quantified by the time required for a 10-fold reduction in the viability of a microbial population at a given temperature
• Heat killing proceeds more rapidly as the temperature rises.
• Time and temperature are directly proportional with each other.
• Physical methods are used extensively in industry, medicine, and the home
• Physical methods can be classified into three classes :

  1. heat
  2. radiation
  3. filtration
• Heat – the most widely used method of physically treating an object or substance to render it sterile
• There are two factors that determine the effectiveness of heat sterilization: time and temperature.
• Higher temperature and shorter time are required to kill pathogens.
• Thermal death time is the time it takes to kill all cells at a given temperature
• The longer time is required to kill all cells in a large population than in a small one
• Moist heat – has more penetrating power and inhibits growth or kills cells more quickly than does dry heat.
• Autoclave – sealed heating device that uses steam under pressure to kill microorganisms
• It is not the pressure inside the autoclave that kills the microorganisms but the high temperatures that are achieved when steam is placed under pressure
• Pasteurization uses heat to significantly reduce rather than totally eliminate the microorganisms found in liquids
• Flash Pasteurization – 71°C for 15 seconds, after which it is rapidly cooled.
• Ultrahigh Temperature (UHT) pasteurization of milk requires heat treatment at 135°C for 1–2 sec and actually sterilizes the milk such that it can be stored at room temperature for long periods without spoilage.
• Dry heat – effective sterilization of metals, glasswares, some powders, oils and waxes.
• incineration (burning) – effective means of destroying contaminated disposable materials; intense heat ignites and reduces microbes to ashes and gas; limited to metals and heatresistant glass materials
• Flaming – accomplished by holding the end of the loop or forceps in the yellow portion of the gas flame; flaming he surface metal forcep and wire bacteriologic loops is an effective way to kill microorganisms
• What type of heat sterilization is this?

  A) dry heat strerilization

  
• Identify the following sterilization methods

  A) incineration

  B) flaming

  
• Identify the type of radiation

  A) ultraviolet radiation

  
• Ionizing Radiation – electromagnetic radiation of sufficient energy to produce ions and other reactive molecular species from molecules with which the radiation particles collide
• Depth filters – important in biosafety applications such as in a biological safety cabinet
• Membrane filters – most common filters used for liquid sterilization
• Nucleopore filters – commonly used to isolate specimens for scanning electron microscopy (SEM)
• Types of filters:

  1. depth filter
  2. membrane filters
  3. nucleopore filters
• Filtration - Used to separate cells, larger viruses, bacteria, certain microbes from liquids or gases in which they are suspended
• Filtration - A unique method of sterilization as it removes contaminants instead of killing them