BIOL 3340 . Chapter 8. Chapter 8. Control of Microorganisms by Physical and Chemical Agents. Figure 8.1-Microbial Control Methods. Definition of Frequently Used Terms in Microbial control methods. Sterilization destruction or removal of all viable organisms from an object or habitat.
Control of Microorganisms by Physical and Chemical Agents
Figure 8.1-Microbial Control Methods
A microbial population is not killed instantly
population death usually occurs exponentially as growth rate (Fig 8.2)
microorganisms were previously considered to be dead when they did not reproduce in conditions that normally supported their reproduction
however we now know that organisms can be in a viable but nonculturable (VBNC) condition
once they recover they may regain the ability to reproduce and cause infection
Decimal Reduction Time (D):
D is the time required to kill 90% of the microorganisms or spores in a sample under specified conditions.
Microorganisms is defined as dead when they don’t grow or reproduce when inoculated in culture medim.
Fig 8.2-Pattern of Microbial death-an exponential plot of survivors against mins of exposure to heating at 121 0C. Note D121is decimal reduction time which is 1 min to kill 90%
Concentration or intensity of an antimicrobial agent:
Duration of exposure:
longer exposure to antimicrobial agents more organisms killed
Figure 8.3-Autoclave Steam Sterilizer
Thermal death time (TDT)
Decimal reduction time (D or D value)
Figure 8.5-Membrane Filter Sterilisation
Figure 8.6-Membrane Filter
Figure 8.7 (a)-Laminar Floor
Figure 8.8-Sterilization with Ionization; Radiation machine which uses Cobalt 60 as a Gamma radiation to sterilize fruits, veg, fish, meat, etc..
These are detergents that have antimicrobial activity and are effective disinfectants
Figure 8.11-Ethylene Oxide Sterilizer
Testing of antimicrobial agents is a complex process regulated by US federal agencies such as: