Plate 49

Establishment of Disease

Skin

• Epithelium – outer part of skin

• Epi: “on”• Theli: “tissue”• Densely packed

cells protect body from invading pathogens

Skin

• Connective tissue – provides cohesion and support to internal structure of the body

• Fibers provide flexibility and form

How do bacteria get into your skin?

Phagocytes

• After a foreign substance has ruptured the skin, phagocyte cells migrate to the site

• Phagein: “to eat”• Cyte: “cell”• Phagocytes – group of immune

cells specialized in “eating” potential pathogens

• Pus from an infection is primarily dead phagocytes

Phagocytosis

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html

Bacterial Enzymes

• Bacteria use enzymes to help establish themselves in the body:– Coagulase– Hyaluronidase– Streptokinase– Hemolysis

Coagulase

• Coagulase is secreted by some bacteria (ex: Staphylococcus)

• Causes proteins in blood to clot

• Commonly found in Gram positive bacteria

• Blood clot surrounds bacteria and protects against phagocytes

Hyaluronidase

• Hyaluronic acid (hyaluronan) is found in epithelial and connective tissues and acts as a “goo” in tissue repair

• Bacteria (ex: Clostridium) secrete hyaluronidase enzyme to breakdown hyaluronic acid

• It allows bacteria to infiltrate skin barrier• Fun fact: sperm secrete hyaluronidase when they come into contact

with an egg

Streptokinase

• Some bacteria (ex: Streptococcus) secrete streptokinase enzyme to dissolve blood clots

• Allows bacteria to spread past the location of initial infection

• Also used in heart attack victims to dissolve arterial blood clots in the heart

Hemolysin

• Some bacteria secrete hemolysin that breakdown cell membranes of red blood cells

• Lowers oxygen levels in blood, improving conditions for anaerobic bacteria (ex: Clostridium)

• Lowers activity of white blood cells and protects bacteria

• Can result in anemia (low levels of RBC)