Staphylococci

Group of gram positive non-motile aerobes cocci spherical in shape arranged in grape like clusters.

Subgroups:

According to the coogulase enzymes presence or absence the staphylococci is divided into two groups.

         i.            Coogulase positive: coogulase enzyme is present e.g. Staphylococcus Aureaus

       ii.            Coogulase negative: coogulase enzyme is absent e.g. Staphylococcus Epidermitis

Habitat:

Staph epidermitis is present in normal flora is Skin, GIT and Respiratory Tract. Staph areaus is never present in normal flora.

Transmission:

·         Direct contact (touching, handling etc)

·         Contaminated ingestion (food, air, drinking etc)

Antigen present in Staph Areaus:

Antigen is any substance which stimulate complement system.

        i.            Peptidoglycan:

                       Produce antibody for own destruction. Antibodies can be detected. It acts as chemotactic factor (neutrophils etc are attracted). It also activates the complement system.

      ii.            Protein A:

                       It causes cooglutination (clumping of bacteria together). The antibodies can be detected in the serum.

Enzymes present in staphylococci:

a.      Catalase:

                       The enzyme present in staphylococci which convert hydrogen per oxide into water and oxygen. Oxygen is released in the form of bubbles which shows the differentiation between the staphylococci and streptococci (catalaseis not present in streptococcus).

b.      Coogulase:

                       The enzyme which convert fibrinogen to fibrin. It causes the coogulation disorders due to clumping of platelets and RBCs.

c.       Hyaluronidase:

                       It causes regradation of connective tissue which causes quick and easy spread of infection. It increases the permeability of connective tissue.

d.      β – lactamase:

                       β – lactamase is enzyme which convert pencillin into pencillinoic acid. The pencillinoic acid has no antibacterial feature.

Toxins:

                       The toxins produced by the staph cocci are the following.

        i.            Exotoxins:

                       A highly potent poison that is produced by a bacterial cell wall causes the breakdown of RBCs and Platelets.

      ii.            Leuocidin:

                       A bacterial toxin that selectively destroys WBCs (leucocytes).

    iii.            Exfoliation:

                       The exfoliation (rupturing) of upper layers of the skin.

     iv.            Toxic shock syndrome Toxins:

                       The toxin which causes the toxic shock syndrome

       v.            Entero-toxin:

                       The toxin which causes food poisoning.

Pathologies:

Local infections:

ü  Abscess

ü  Furuncle (hair follicle involvement)

ü  Acne, Pimple (small inflamed swelling on skin that contains pus)

Systemic infection:

Ø  Osteomyelitis

Ø  Meningitis endocarditis

Ø  Pylonephritis

Ø  Pneumonia

Ø  Scalded skin syndrome:

                       It is due exfoliation of skin. It is eruption of small swellings, upper layer of skin is gone (post Burn skin)

Ø  Toxic shock syndrome:

                       Due to toxic shock syndrome toxin characterized by fever, septicemic shock and multiple organ failure.

Diagnostic lab tests:

                       The specimen can be blood serum, urine, stool, and swab (eyes, skin, vagina, anus, CSF)

v  Microscopy

v  Gram Stainy

v  Culture and sensitivity

v  Serological tests:

                       Antibodies titre from serum

v  Immunization:

                There is no passive immunization (vaccination) for staphylococci.