Factors affecting the efficacy of disinfection and sterilization

Factors:

1.Number and location of microorganisms
2.Innate resistance of microorganisms
3.Concentration and Potency of disinfectants 
4.Physical and Chemical factors
5.Organic and Inorganic matter
6.Duration of exposure
7.Biofilms


Number and location of microorganisms:
all others condition remaining constant, the larger number of microbes need more time to elimination all of them, because this reason, people need to scrupulous cleaning of medical instruments before disinfection and sterilization. It can reduce many microorganisms on the instruments. increases the margin of safety when the germicide is used according to the labeling and shortens the exposure time required to kill the entire microbial load. 

Innate resistance of microorganisms:
microorganisms vary greatly in their resistance to chemical germicides and sterilization processes, intrinsic resistance mechanisms in microorganisms to disinfectants vary. the user needs to employ exposure times and a concentration of germicide needed to achieve complete destruction.

Concentration and Potency of disinfectants:
with other variables constant, high concentrated has the greater efficacy and the shorter time necessary to achieve microbial kill than the low concentrated.Considering the length of the disinfection time, which depends on the potency of the germicide,also is important. This was illustrated by Spaulding who demonstrated using the mucin-loop test that 70 percent isopropyl alcohol destroyed 10000 M.tuberculosis in 5 mins,whereas a simultaneous test with 3 percent phenolic required 2-3 hours to achieve the same level of microbial kill.

Physical and Chemical factors:
several physical and chemical factors also influence disinfectant procedures:temperature,PH,relative humidity,and water hardness.

Organic and Inorganic matter:
Organic matter in the form of serum, blood, pus, or fecal or lubricant material can interfere with the antimicrobial activity of disinfectants.The effects of inorganic contaminants on the sterilization process were studied during the 1950s and 1960s.　These and other studies show the protection by inorganic contaminants of microorganisms to all sterilization processes results from occlusion in salt crystals, so the cleaning before sterilization and disinfection is very important. organic and inorganic matter are very easy to remove by washing.

Duration exposure:
items must be exposed to the germicide for the appropriate minimum contact time.

Biofilms:
Microorganisms may be protected from disinfectants by production of thick masses of cells and extracellular materials, or biofilms.