This chapter discusses various methods for controlling microbial growth, including physical, chemical, and other approaches. It defines key terms and describes how different techniques like heat, radiation, filtration and chemicals impact microbial cells. Specific methods are outlined, such as how autoclaving, pasteurization, and dry heat kill microbes. The mechanisms and optimal uses of various disinfectants and antiseptics are also explained.
Factors influencing death curve:
initial population size on the time necessary to sterilize something.
Presence of organic matter inhibits action of chemical antimicrobials.
Time of exposure
Microbial characteristics
The susceptibility of the plasma membrane is due to its lipid and protein components.
2.Certain chemical control agents damage the plasma membrane by altering its permeability.
Some microbial control agents damage cellular proteins by breaking hydrogen bonds and covalent bonds.
4.Other agents interfere with DNA and RNA replication and protein synthesis.
Heat is frequently used to kill microorganisms.
2.Moist heat kills microbes by denaturing enzymes.
Cl. Perfringens and botulinum (food poisoning) survive hours of boiling. Also very resistant Large numbers of hepatitis A virus, fungal spores and protozoal cysts.
UHT-pasteurized milk that is packaged aseptically results in a "shelf stable" product that does not require refrigeration until opened
Hot air sterilization: Glassware is heated for 2-3 hours at 320º-360ºF (160º-180ºC)
Also used for powder, water free oils
Advantage: no dulling and corrosion
Pseudomonas very resistant to triclosan
The oligodynamic effect (Greek oligos = few, dynamis = force) was discovered in 1893 by the Swiss KW Nägeli as a toxic effect of metal-ions on living cells, algae, molds, spores, fungus, virus, prokaryotic and eukaryotic microorganisms, even in relatively low concentrations. This antimicrobial effect is shown by ions of: mercury, silver, copper, iron, lead, zinc, bismuth, gold, aluminium and other metals.