1. Chemical Methods of Disinfection Fe A. Bartolome, MD,
FPASMAP Department of Microbiology Our Lady of Fatima
University
2.
Sterilization
Killing of all microorganisms, including bacterial spores
Disinfection
Reducing the number of bacteria to a level low enough that
disease is unlikely to occur
Some organisms and bacterial spores may survive
3.
Antiseptics
Chemicals used to kill micro-organisms on the surface of skin
and mucous membranes
4.
Differ from systemically-active anti-microbials in that they
possess little selective toxicitytoxic not only for microbial
pathogens but for host cells as well
Can be used only to inactivate microorganisms in the inanimate
environment or, to a limited extent, on skin surfacescannot be
administered systemically
High temperature speeds up rate of chemical reaction
Nature of surrounding medium
pH of medium; presence of extraneous materials like pus or
blood
Nature of the organism
Ability to produce spores; number & size of inoculum
6.
Characteristics of a good chemical disinfectant or
antiseptic:
Able to destroy a wide variety of microorganisms
Fast-actingshort contact time
Not affected by the presence of other substances such as
organic matter
Non-toxic to human tissues as well as non-corrosiveand
non-destructive to materials for which it is used
Should leave a residual antimicrobial film on the treated
surface
Water-soluble and easy to apply
Inexpensive and easy to prepare
Stable under storage and shipping conditions
Odorless
7.
Damage Cell Membrane
Surface active agents interact with the lipid in the cell
membranedisrupt cell membrane
Cationic agents
Quarternary ammonium compounds
Cationic detergents widely used for skin antisepsis
Effective at alkaline pH
Example: zephiran, benzalkonium chloride
8.
Damage Cell Membrane
Surface active agents
Anionic agents
Remove dirt through the process of emulsification
Effective at acidic pH
Example: soaps and detergents
Composed of long-chain, lipid-soluble, hydrophobic portion and
a polar hydrophilic portion
9.
Damage Cell Membrane
Phenolic compounds also denature proteins
Phenol
No longer used due to toxicity
Mainly used as gold standard in the evaluation of new chemical
agents using the phenol coefficient test
Ratio of the concentration of phenol to the concentration of
the agent required to cause the same amount of killing under
standard conditions of the test
10.
Damage Cell Membrane
Phenolic compounds
Cresols (Methylphenol)
Phenol derivatives
More potent and safer
Example: lysol
Hexachlorophene
Biphenol with six chlorine atoms
Used in germicidal soaps
With possible neurotoxicity
11.
Damage Cell Membrane
Alcohols also denatures proteins
Ethanol
Bactericidal
Remove lipid from skin surface
Widely used to clean the skin before immunization or
venipuncture
Requires presence of water for maximal activitymore effective
at 70%
12.
Damage Cell Membrane
Alcohols also denatures proteins
Isopropyl alcohol
Greater bactericidal activity than ethanol; less volatile
Side effect: narcosis due to inhalation of fumes
Benzyl alcohol used as preservative
13.
Denaturation of Cellular Proteins
Acids and alkali
Strong acids and alkali bactericidal
Mycobacteria resistant to 2% NaOH (used in clinical laboratory
to liquefy sputum prior to culture)
Weak acids (benzoic, propionic, and citric acids) used as food
preservatives
Alcohol and acetone
Phenol and cresol
14.
Modify Functional Groups of Proteins and Nucleic acids:
Heavy Metals damage enzyme activity of bacteria by binding to
sulfhydryl groups