Friday, March 8, 2013

TECHNIQUES IN CONTROL OF MICROORGANISMS

DISINFECTION & STERILIZATION  TECHNIQUES IN MICROBIOLOGY:


  • Sterilization is the complete destruction or removal of all forms of life including viruses & spore forming bacteria. The term 'Sterile' therefore refers to complete absence or destruction of all microorganisms.
            Disinfection is the process by which causative, pathogenic & harmful microorganisms are killed or inhibited. This process is usually carried by chemical agents. Disinfectants are agents used to carry out disinfection on inanimate objects.
          Different Terminology Used in Microbes Control:
  • Antiseptics:  It is an agent used to carry out disinfection on living objects like tissue of human body. It prevents sepsis or growth of pathogens on the tissues.
  • Asepsis: It is the employment ( such as  usage of gloves, air filters, UV rays etc)  to achieve microbes free environment,
  • Sanitization:   It is the reduction of microbial population to a safe level as determined by local public health standard. 
  • Surfactants: To disinfect surface (whether inanimate or animate objects)
  • Germicide:  Chemicals used to kill germs.
  • Fungicide: Chemicals used to kill fungus.
  • Sporicide: Chemicals used to kill Spores. 
  • Virucide: Chemicals used to kill viruses. 
  • Bactericidal Agent: An agent that kills microorganisms .It may inactivates the major enzymes & interfere with it's metabolism, so it dies. 
  • Bacteriostatic Agent: An agent that temporarily prevents their further multiplication without necessarily killing them. It disturbs a minor chemical reaction & slows the metabolism resulting in longer time between cell division.

MODE OF ACTION OF ANTIMICROBIAL AGENTS:
                                              Many antimicrobial agents can cause damage to the cells at many sites.Antimicrobial agents inhibit or kill the microorganism by following manner; 
  • Damage to cell wall Or Inhibition Of Cell Synthesis.
  • Alteration of Permeability of Cytoplasmic Membrane. 
  • Alteration of Physical or chemical state of Proteins & Nucleic Acids
  • Inhibition Of Enzyme Action 
  • Inhibition of Protein Or nucleic acids synthesis.
Factors Affecting Antimicrobial Agents:
  1. Factors Related to Killing Agents Or Antimicrobial Agents:
a). Intensity: Intensity is generally related to temperature. Spore of Clostridium botulinum  are heat resistance & don't die when boiled at 100 degree Celsius for several hours, but at 113 degree celsius it can be killed in 60 minutes, At 114 it can be killed in 39 minutes, At 115 it can be killed in 10 minutes.
As temperature increases, time required to kill spores decreases.
Concentration is used if the agent is Chemical . Eg; 0.1% phenol don't kill E.coli , but only prevents growth 
1% phenol kills within 20-30 min , 5% phenol kill within 2-3 min . Therefore, if concentration increases, the time duration to kill bacteria decreases. 
b). The time & agent can kill:  For the effectiveness of antimicrobial agents there should be sufficient time for contact between agent & microorganisms. 
c). Temperature: Temperature much above optimal growth temperature, for a given mos generally produce greater death rate than growth rate.  

2. Factors Related to Organisms to be killed: 
i) No of Organisms to be killed: Efficacy of an antimicrobial agent is  inversely proportional to microbial load. ie greater the load, longer the time to kill all of them.
ii. Type Of Organisms:  Organisms  like spore-former's are most resistance to heat & temperature compared to non-spore former's. 
iii. Physiological State of Cells: Young & actively metabolizing cells are more easily destroyed than old & dormant cells. 

3. Environmental Factors:  
  • Effectiveness of heat is greater in acid than in alkaline medium.
  • High concentration  of carbohydrates generally increase thermal resistance of microorganisms.
  •  Presence of organic matter( blood, sputum, tissues) reduces efficacy of antimicrobial agents either by inactivating it or by protecting it.








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