BIOL 2320 J.L. Marshall, Ph.D. HCC-Stafford Campus 1 Chapter 13 –Microbe-Human Interactions: Infection, Disease, and Epidemiology* *Lecture notes are to be used as a study guide only and do notrepresent the comprehensive information you will need to know for the exams. Important Terminology Infection –A condition in which pathogenic organisms penetrate the host defenses, enter the tissues, and multiply. Diseaseis any change from the general state of good health when the cumulative effects of the infection disrupt or damage tissues and organs. For the sake of this course, infectious diseases will be studied as opposed to genetic, physiological diseases or diseases caused by nutritional problems. Normal flora–A diverse group of microbes (mostly bacteria) adapted to live in the human body and on the skin surface. Many of the normal flora of the large intestine (E.colifor example) are actually very beneficial to us and our relationship with them can be characterized as mutualistic symbiosis. However, S. aureus that typically colonizes the skin can be dangerous if allowed to grow systemically.(Table 13.1, pg. 389; Table 13.3, pg. 390)Symbiosisis a relationship in which two organisms interact in close association usually with benefits to both species. We give E.colia place to live and food, while the E.coligives us protection against pathogens and a significant source of vitamin K. Parasitismis the opposite of a mutualistic relationship: One organism benefits (parasite) and one suffers (host). When S. aureusis growing systemically in a human, the bacteria are getting food and a place to grow, while we aren’t getting anything in return, and worse, are being harmed by the exotoxins and exoenzymes the bacteria produce. An ideal parasite is one that can enter a host, survive and reproduce in large numbers, and then move on to a new host.Pathogenicityis the ability of a parasite to gain entry to host tissues and cause disease. Organisms that can cause disease are referred to as pathogens. Opportunistic pathogenis one that invades the tissues when body defenses are suppressed. They might be part of the normal flora, but become capable of causing disease under certain circumstances such as when someone has AIDS, is taking immunosuppressant drugs, or suffers a superinfection as a result of antibiotic therapy. True pathogen–also known as primary pathogens, these infectious microorganisms are capable of causing infection and disease in healthy personswith normal immune defenses. They are generally associated with a distinct recognizable disease (e.g. Mycobacterium tuberculosis= tuberculosis).