CONTROL OF MICROBIAL GROWTH


1. Controlling Microbial growth is necessary

2. Factors influencing the effectiveness of control methods

A number of factors affect the usefulness (efficacy) of control methods & all factors should be considered to devise control measures

Methods for controlling microbial growth

 

Physical Methods of controlling microbial growth

Method
 Mechanism of Action
 Comments
 Preferred Use
1. Moist Heat(A)
    a. Boiling Denaturation Kills vegetative cells but not spores Equipment, dishes
    b. Autoclaving Denaturation  Sterilization (autoclaves, pressure cookers, retorts) Media, linens, equipment, dressings
     c. UHT Denaturation Sterilization; 141oC / 2secs Milk falls in a thin film thro a chamber of superheated steam
2. Dry Heat(A)
    a. Flaming Burning to ashes Sterilization Inoculating loops
    b. Incineration Burning to ashes Sterilization animal cacasses, dressings, wipes
    c. Hot-air  
        sterilization
Oxidation 170oC / 2hrs Glassware, needles, glass syringes
3 Pasteurization(A)    
    a. Low temp  
        long  time  
        (LTLT)
Denaturation 63oC/30mins Milk: batch process in tanks
    b. High temp,  
         short time  
         (HTST)
Denaturation 72oC / 15secs Milk: Flash method thro continous winding pipe
4. Filtration(B) Separation Liquid thro screen Heat labile material
5. Low Temp
 a. Fridge Growth slows Bacteriostatic  Drug, Food
 b. Deep Freezing Growth slows Preservation -70oC Drug, food & culture 
6. Desiccation(C)
a. Lyophilization Growth arrested Long term preservation of microbes Food, Drug & culture
b. Osmotic Pressure Plasmolysis Loss of water Food preservation
8. Radiation(D)
 a. Ionizing DNA destruction Not commonly used Sterilizing medical & dental supplies
 b. Nonionizing  DNA py-py dimers (eg UV) Not very penetrating radiation  UV (germicidal) lamp
 
  (A) Moist Heat is used extensively by the food (canning & milk) industry (B) Filtration is used for sterilizing heat-labile liquids and to sterilize air (gas) for creating aseptic environment (physical removal of microbes)

(i) Liquids:

(ii) Air: (C) Cells require water for metabolic activities. Desiccation is a process by which water is removed and therefore growth is affected
  (D) Electromagnetic radiation causes cellular damage

Chemical methods of controlling microbial growth

Microbiology laboratory standards, design and safety


ss12bmi 
Author and HTML'd by: Dr Bharat Patel <B.Patel@griffith.edu.au

[Created 25 Sept 1995]
[Modified 29 Aug 1997]