Micro Topic 8 - TOPIC 8 PRINCIPLES OF DISEASE AND...

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TOPIC 8 – PRINCIPLES OF DISEASE AND PATHOGENICITY I. PRINCIPLES OF DISEASE (Chapter 14) 1. PATHOLOGY, INFECTION AND DISEASE a) Pathology is the study of disease. b) Pathogens are microbes that cause disease. They have special properties that allow them to invade the human body and/or produce toxins. c) Etiology is the cause of disease. d) Pathogenesis is the way in which a disease develops. e) Disease is an abnormal state that can occur after infection by a microbe. Infection does not necessarily cause disease. 2. NORMAL MICROBIOTA (Figure 14.2 pg 410 and Table 14.1 pg 411) a) Animals, including humans, are usually germ-free while in the uterus. b) Microbes begin colonization (growing) in and on the surface of the body soon after birth. c) Microbes that are established in the body but don’t cause disease make up the normal microbiota (normal flora). a. Normal flora and the host exist together: this is symbiosis. There are 3 types of symbiosis i. Commensalism – one organism benefits, the other is unaffected. ii. Mutualism – both organisms benefit. iii. Parasitism – one organism benefits, the other is harmed. d) Microbes that are present for a while and then disappear are known as transient microbiota. A. RELATIONSHIPS BETWEEN THE NORMAL MICROBIOTA AND THE HOST b) The normal microbiota can prevent pathogens from causing an infection. c) This is microbial antagonism e.g. normal flora prevents growth of Candida albicans in vagina. d) Normal flora out-compete the invading pathogen by: a. Competing for nutrients b. Producing toxic substances c. Changing conditions e.g. pH 1
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B. OPPORTUNISTIC MICROORGANISMS a) Opportunistic microbes do not usually cause disease but might do so in a different environment e.g. S. pneumoniae, found in nose and throat, may cause pneumonia. C. COOPERATION AMONG MICROORGANISMS a) Cooperation occurs when one microbe makes it possible for another to cause a disease or to produce more severe symptoms e.g. Streptococci in the mouth help pathogenic microbes attach to the teeth and cause decay. 3. ETIOLOGY OF INFECTIOUS DISEASES a) The etiology of some diseases is well understood (e.g. polio) but for others, it is not well understood (H. pylori) or even known (Alzheimers). A. KOCH’S POSTULATES (Figure 14.3 pg 414) a) Koch's postulates are a method for establishing that specific microbes cause specific diseases . b) Koch's postulates have the following four requirements: a. The same pathogen must be present in every case of the disease; b. The pathogen must be isolated from the host and must be grown in pure culture; c. The pathogen isolated from pure culture must cause the same disease in a healthy, susceptible laboratory animal when inoculated into that animal; d. The pathogen must be isolated from the inoculated laboratory animal and shown to be identical to the original microbe.
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