Hydrogen peroxide:
H2O2 effects are direct and indirect actions of O2 as it forms hydroxyl free radical which is highly toxic and reactive to cell. As an antiseptic, 3% H2O2 serves a variety of needs including skin and wound cleansing, bedsore care and mouth washing. It is especially useful in treating infection by anaerobic bacteria because of the lethal effects of O2 on these forms. When it is applied to a wound, the enzyme catalase in the tissue decomposes the H2O2 into water and free O2. The O2 causes the wound tissues to bubble and the bubbling removes microorganisms mechanically. Also, the sudden release of O2 brings about chemical changes in certain microorganisms, and these changes lead to microbial death.
Acids and alkalis:
Conditions of very low or high pH can destroy or inhibit microbial cells; but they are limited in application due to their corrosive, caustic and hazardous nature. Aqueous solutions of ammonium hydroxide remain a common component of detergents, cleansers and deodorizers. Organic acids are widely used in food preservation because they prevent spore germination and bacterial and fungal growth. Acetic acid (in the form of vinegar) is a pickling agent that inhibits bacterial growth; propionic acid is commonly incorporated into breads and cakes to retard moulds, benzoic acid and sorbic acids are added to beverages, syrups etc to inhibit yeasts.
The best known disinfectant screening test is the phenol coefficient test in which the potency of a disinfectant is compared with that of phenol. A series of dilutions of phenol and the experimental disinfectant are inoculated with the test bacteria Salmonella typhi and Staphylococcus aureus , then placed in a 20 or 37°C bath. These inoculated disinfectant tubes are next subcultured to regular fresh medium at 5 min interval, and the subcultures incubated for two or more days. The highest dilutions that kill the bacteria after a 10 min exposure, but not after 5 min, are used to calculate the phenol coefficient. The reciprocal of the appropriate test disinfectant dilution is divided by that for phenol to obtain the coefficient. Suppose that the phenol dilution was 1/90 and maximum effective dilution for disinfectant X was 1/450. The phenol coefficient of X would be 5. The higher the coefficient value, the more effective the disinfectant under these test conditions. A value greater than 1 means that the disinfectant is more effective than phenol.
REFERENCES:
Text Books:
1. Jeffery C. Pommerville. Alcamo's Fundamentals of Microbiology (Tenth Edition). Jones and Bartlett Student edition.
2. Gerard J. Tortora, Berdell R. Funke, Christine L. Case. Pearson - Microbiology: An Introduction. Benjamin Cummings.
Reference Books:
1. Lansing M. Prescott, John P. Harley and Donald A. Klein. Microbiology. Mc Graw Hill companies.