General aspects – Remember definition: organisms frequently found on or within body of healthy individuals – Most are bacteria, but some are viruses, fungi, and protozoa

Microbial pathogenesis—process of causing disease Colonization—presence of microbes at site of body – Does not imply tissue damage or disease symptoms – Does imply invasion of site and multiplication

American Legion Convention in 1976 in Philadelphia hotel – Respiratory distress and fever – 200 affected – 34 died

General Aspects Ecology – Found throughout the environment Very simple nutritional requirements – Not usually in normal flora unless hospitalized or immunocompromised

Diversity of species Ecology – Found worldwide in soil, water, vegetation, and microbial flora of animals and humans – Some are always associated with disease

Comparison of Meningococcus and Gonococcus Pathobiology Similarities: – Both diploccocci – Share about 80% DNA – Neither makes exotoxin; both make endotoxin – Both are relatively good colonizers

Staphylococci Important human pathogen – Causes both relatively minor and serious diseases One of the hardiest of the non￾sporeforming bacteria – Can exist on dry surfaces for a long period – Relatively heat-resistant; temperature range

Definition – Soluble substances that alter normal metabolism of host cells with deleterious effects on the host Host range – Known for bacteria, but possible that they play a role in diseases caused by fungi

Production of Ab and Activation of Macrophages and Cytotoxic T Cells T-Dependent T-Independent

Arthur Kornberg (1918- ) of the U.S. produced DNA in a test tube. F. Sanger (1918- ) of Britain developed sequencing procedure for proteins, and later for DNA