Enzymes:

Serum lysozyme:

Provides innate & nonspecific immunity
Lysozyme is a hydrolytic enzyme capable of digesting bacterial cell walls containing peptidoglycan 
•    In the process of cell death, lysosomal NZs fxn mainly to aulolyse necrotic cells (NOT “mediate cell degradation”)
•    Attacks bacterial cells by breaking the bond between NAG and NAM.
•    Peptidoglycan – the rigid component of cell walls in most bacteria – not found in archaebacteria or eukaryotic cells
•    Lysozyme is found in serum, tears, saliva, egg whites & phagocytic cells protecting the host nonspecifically from microorganisms

Superoxide dismutase: catalyzes the destruction of O2 free radicals protecting O2-metabolizing cells against harmful effects 

Catalase:

- catalyzes the decomposition of H2O2 into H2O & O2
- Aerobic bacteria and facultative anaerobic w/ catalase are able to resist the effects of H2O2
- Anaerobic bacteria w/o catalase are sensitive to H2O2  (Peroxide), like Strep
- Anaerobic bacteria (obligate anaerobes) lack superoxide dismutase or catalase
- Staph makes catalase, where Strep does not have enough staff to make it

Coagulase

- Converts Fibronogen to fibrin
•    Coagulase test is the prime criterion for classifying a bug as Staph aureus – from other Staph species
•    Coagulase is important to the pathogenicity of S. aureus because it helps to establish the typical abscess lesion 
•    Coagulase also coats the surface w/ fibrin upon contact w/ blood, making it harder to phagocytize

DISINFECTION AND STERILIZATION

•    Sterilization is the best destruction or com removal_of all forms of micro organisms.
•    Disinfection is the destruction of many microorganisms but usually the b spores.
•    Antisepsis is the destruction or inhibition of microorganisms in living tissues thereby limiting or preventing the harmful effect of infection.
•    Astatic Agent  would only inhibit the growth of microorganisms (bacteriostatic, fungistatic, sporostatic).
•    Acidal agent would kill the microorganism (bactericidal. virucidal, fungicidal)
•    Sterilants are the chemicals which under controlled conditions can kill sporinQ bacteria.
 

CHEMICAL AGENTS

Chlorine and iodine are most useful disinfectant Iodine as a skin disinfectant and chlorine as a water disinfectant have given consistently magnificent results. Their activity is almost exclusively bactericidal and they are effective against sporulating organisms also. 
Mixtures of various surface acting agents with iodine are known as iodophores and these are used for the sterilization of dairy products.

Apart from chlorine, hypochlorite, inorganic chioramines are all good disinfectants but they act by liberating chlorine. 

Hydrogen peroxide in a 3% solution is a harmless but very weak disinfectant whose primary use is in the cleansing of the wound.
 
Potassium permanganate is another oxidising agent which is used in the treatment of urethntzs. 

Formaldehyde — is one of the least selective agent acting on proteins. It is a gas that is usually employed as its 37% solution, formalin. 

When used in sufficiently high concentration it destroys the bacteria and their spores.

Classification of chemical sterilizing agents

Chemical disinfectant

Interfere with membrane functions

•    Surface acting agents : Quaternary ammonium, Compounds, Soaps and fatty acids

•    Phenols : Phenol, cresol, Hexylresorcinol

•    Organic solvent : Chloroform, Alcohol

Denatures proteins

•    Acids and alkalies : Organic acids, Hydrochloric acid , Sulphuric acid

Destroy functional groups of proteins

•    Heavy metals :  Copper, silver , Mercury

•    Oxidizing agents: Iodine, chlorine, Hydrogen peroxide

•    Dyes : Acridine orange, Acriflavine

•    Alkylating agents : Formaldehyde, Ethylene oxide

Applications and in-use dilution of chemical disinfectants

Alcohols : Skin antiseptic Surface disinfectant, Dilution used 70%

Mercurials : Skin antiseptic Surface disinfectant Dilution Used 0.1 %

Silver nitrate : Antiseptic (eyes and burns)  Dilution Used 1 %

Phenolic compound : Antiseptic skin washes  Dilution Used .5 -5 %

Iodine : Disinfects inanimate object, Skin antiseptic Dilution used  2%

Chlorine compounds  : Water treatment Disinfect inanimate objects , Dillution used 5 %

Quaternary ammonium Compounds : Skin antiseptic , Disinfects inanimate object, Dilution Used < 1 %

Glutaraldehyde: Heat sensitve instruments, Dilution used 1-2 %

Cold sterilization can be achieved by dipping the precleaned instrument in 2% solution of gluteraldehyde for 15-20 minutes. This time is sufficient to kill the vegetative form as well as spores ofthe organisms that are commonly encountered in the dentistry.

Ethylene oxide is an a agent extensively used in gaseous sterilization. It is active against all kinds of bacteria and their spores. but its greatest utility is in sterilizing those objects which are damaged by heat (e.g. heart lung machine). It is also used to sterlise fragile, heat sensitive equipment, powders as well as components of space crafts.

Evaluation of Disinfectants

Two methods which are widely employed are:

 Phenol coefficient test, Kelsey -Sykes test
 
These tests determine the capacity of disinfectant as well as their ability to retain their activity.
 

ANTIGEN-ANTIBODY REACTIONS

Affinity of the antigen-antibody reaction refers to the intensity of the attraction between antigen and antibody molecule.
Antigen-antibody reactions

Reaction test            Modified test

Precipitation  -> Immunoelectrophoresis, Immunoprecipitation
Agglutination -> Latex agglutination, Indirect, Haemagglutination , Coagglutination ,Coombs test

Neutralization  -> Measurement of LD, Plaque assays

Complement fixation  -> Conglutination

Immunofluorescence ->  Indirect immunofiuorescence, Immunoofluoremetric Assay

Enzyme immunoassay -> Enzyme linked, Immunosorbent assay

Radioimmunoassay -> Immunoradiometric assay

Avidity is the strength of the bond after the formation of antigen-antibody complex.

Sensitivity refers to the ability of the test to detect even very minute quantities of antigen or antibody. A test shall be called as highly sensitive if false negative results are absent or minimal.

Specificity refers to the ability of the test to detect reactions between homologous antigens and antibodies only, and with no other. In a highly specific test, false positive reactions will be minimal or absent.

ANTIGEN-ANTIBODY REACTIONS

I. NATURE OF ANTIGEN-ANTIBODY REACTIONS

A. Lock and Key Concept 

The combining site of an antibody is located in the Fab portion of the molecule and is constructed from the hypervariable regions of the heavy and light chains. Antigen-antibody reactions is one of a key (i.e. the antigen) which fits into a lock (i.e. the antibody).

B. Non-covalent Bonds 

The bonds that hold the antigen to the antibody combining site are all non-covalent in nature. These include hydrogen bonds, electrostatic bonds, Van der Waals forces and hydrophobic bonds. 

C. Reversibility
Since antigen-antibody reactions occur via non-covalent bonds, they are by their nature reversible.
II. AFFINITY AND AVIDITY

A. Affinity 
Antibody affinity is the strength of the reaction between a single antigenic determinant and a single combining site on the antibody. It is the sum of the attractive and repulsive forces operating between the antigenic determinant and the combining site of the antibody .

B. Avidity
Avidity is a measure of the overall strength of binding of an antigen with many antigenic determinants and multivalent antibodies. Avidity is influenced by both the valence of the antibody and the valence of the antigen. Avidity is more than the sum of the individual affinities.

III. SPECIFICITY AND CROSS REACTIVITY

A. Specificity 

Specificity refers to the ability of an individual antibody combining site to react with only one antigenic determinant or the ability of a population of antibody molecules to react with only one antigen. In general, there is a high degree of specificity in antigen-antibody reactions. 

B. Cross reactivity 

Cross reactivity refers to the ability of an individual antibody combining site to react with more than one antigenic determinant or the ability of a population of antibody molecules to react with more than one antigen.