DISINFECTION

DEFINITION:

The freeing of an article from some living organisms,

i.e. killing many but not all micro-organisms.

METHODS:1. Heat Disinfection: @ To disinfect eating utensils and

clothing at a temp. of 70˚C for several minutes.

2. Chemical Disinfectants: @ Commonly used : phenol &

hypochlorite

@ Drawback : liable to be rendered inactive by undue dilution, by contact with organic matter (dirt, pus, blood).

CLASSIFICATION :1. Strong Disinfectants: @ Very potent, but toxic to Man. @ Not used for skin or tissues

(formalin)

2. Mild Disinfectants (Antiseptics): @ Non-toxic

@ Applied to tissue & skin ( alcohol, iodine, soap ) By definition : an antiseptic is a

chemical used to kill organisms on skin & mucous membranes.

FACTORS INFLUENCING DISINFECTION:

1. Concentration of disinfectant:

@ Disinfectant is used at its right concentration and dilution .

2. Time of application: @ Depends on nature & concentration

of disinfectant.

3. Number of organisms present.

4. Nature of organisms present :

@ e.g.: vegetative forms or spore-

bearers. @ Doubtful action on

endospores.

5. Presence of heat: @ Increases rate of action of disinfectant.

6. pH of disinfectant: @ Action depends on correct

pH .

7. Hardness of water :

@ some antiseptics are affected by hard water (soap)

8.Organic matter :

@ Reduces efficiency of a disinfectant (pus, blood, dirt).

ADVANTAGES

Before disposal or re-use :

@ Bed-pan, clothes, clinical thermometer, tongue depressor, specula, slides, pipette @ Best : phenol and hypochlorite .

2.Reduction of environment microbes :

@ Floor, walls, furniture, theater, Kitchen: soap, phenol, hypochlorite,

alcohol @ Room : by formaldehyde gas .

3.Skin, hands & operation site :

@ Use soap, chlorhexidine, iodine, alcohol

PROPERTIES AND USES OF DISINFECTANTS

1.Phenol group:

@ Phenol (carbolic acid) : cheap, powerful, microbicidal, active against many organisms, not affected by organic matter (include: lysol, cresol)

@ Chlorophenols (Dettol) : less toxic, affected by organic matter

2. The halogens:

@ Bactericidal : chlorine and iodine

* Chlorine: to disinfect water, affected by organic matter, e.g. :

• Eusol: used in hospitals. • Hypochlorite (Clorox): not applied to

cloth or to metal .

* Iodine: Affected by organic matter, powerful, rapid disinfectant, irritant .

3. Metallic salts:

a)Mercuric chloride:

@ Bacteriostatic, used to inactivate vaccines, to preserve antitoxins and anti-sera.

b) Silver nitrate: used for extensive burns.

4. Formaldehyde+ Glutaraldehyde

@Formaldehyde:

kills organisms & spores, cheap, used as gas to

disinfect rooms, & as solution to sterilize benches.

@ Glutaraldehyde:

active against spores, used for cystoscopes,

thermometers, plastic materials.

5. Volatile solvents:

a)Isopropyl & ethyl alcohol:

@ Bactericidal at dilution 70-75%, action is lowered when absolute, or when over-diluted, used for injections & drips.

b) Acetone & ether :

@ Weak as a disinfectant

c) Chloroform: @ Bactericidal, disappears quickly when

applied, not widely used.

6. Soap & Detergents:

@ Soap: mechanical removal of organisms on washing.

@ Other detergents : ammonium compounds are bacteriostatic.

@ Cetrimide (Cetavlon): inactive against Pseudomonas.

7. Aniline & acridine dyes

@ Active against gram +ve organisms, bactericidal, used in presence of organic matter

@ Gentian violet: used for burns.

GASEOUS DISINFECTANTS:

1. Formaldehyde gas:

@ Used to sterilize air in rooms, fomites @ Exposure to continue for 3 hrs, @ Spray ammonia to remove formaldehyde

residues.

2. Ethylene oxide:

@ Kills organisms & spores, used for plastic & rubber articles, blankets,

@ Toxic, explosive when mixed with air,

TESTS OF DISINFECTANTS:

1. Rideal-Walker Test.

2. Chick-Martin Test

3. Determination of the number of viable organisms after application of disinfectant by bacterial count technique.

Rideal-Walker & Chick-Martin tests:

@ Apply phenol coefficient which is a quantitative measurement of the ability of a disinfectant to kill a micro-organism.

By definition: a phenol coefficient is a ratio of concentration of phenol to concentration of disinfectant required to give same amount of killing under standard conditions i.e.

Phenol coefficient ratio =Concentration of phenol

Concentration of disinfectant

MECHANISM OF ACTION

1. Disruption of cell membrane:

@ Alcohol: disorganizes lipid structure of cell membrane & denatures cell proteins.

@ Detergents: interact with lipid layer of cell membrane

@ Phenols: damage cell membrane & denature proteins.

2. Modification of proteins:

a)Chlorine: interact with cell enzymes to form the inactive disulphide compound.

b) Iodine: inactivates cell enzymes & denatures cell proteins.

c) Heavy metals: block cell enzyme activity, i.e. Hg & Ag.

d) Hydrogen peroxide: inhibits enzymatic activity of cell.

e) Formaldehyde: denature proteins & nucleic acids.

f) Glutaraldehyde: same action as formaldehyde, ten times more effective.

g) Ethylene oxide: denature proteins and modifies nucleic acids of cell.

h) Strong acids & alkalis: H2SO4 and Na

OH denature proteins.

3. Nucleic acids Modification :

a) Crystal (gentian) violet dye : Binds to the phosphate group of nucleic acid.

b) Malachite green dye: has same action as crystal violet.