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Fungi fungi exist in either yeast or mold forms the

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Fungi Fungi exist in either yeast or mold forms. The smallest of yeasts are similar in size to bacteria, but most are larger (2 to 12 m) and multiply by budding. Molds form tubular extensions called hyphae, which, when linked together in a branched network, form the fuzzy structure seen on neglected bread. Fungi are eukaryotic, and both yeasts and molds have a rigid external cell wall composed of their own unique polymers, called glucan, mannan, and chitin. Their genome may exist in a diploid or haploid state and replicate by meiosis or simple mitosis. Most fungi are free-living and widely distributed in nature. Generally, fungi grow more slowly than bacteria, although their growth rates sometimes overlap. Parasites Parasites are the most diverse of all microorganisms. They range from unicellular amoebas of 10 to 12 m to multicellular tapeworms 1 meter long. The individual cell plan is eukaryotic, but organisms such as worms are highly differentiated and have their own organ systems. Most worms have a microscopic egg or larval stage, and part of their life cycle may involve multiple vertebrate and invertebrate hosts. Most parasites are free-living, but some depend on combinations of animal, arthropod, or crustacean hosts for their survival. Normal Microbial Flora Origin and Nature Normal Flora at Different Sites Blood, Body Fluids, and Tissues Skin Intestinal Tract Respiratory Tract Genitourinary Tract Roles in Health and Disease
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Opportunistic Infection Exclusionary Effect Priming of Immune System Promoting "Good" Flora Before moving on to discuss how, when, and where the previously mentioned agents cause human disease, we should note that the presence of microbes on or in humans is not by itself abnormal. In fact from shortly after birth on it is universal; that is, normal. The term normal flora is used to describe microorganisms that are frequently found in various body sites in normal, healthy individuals. The constituents and numbers of the flora vary in different areas of the body and sometimes at different ages and physiologic states. They comprise microorganisms whose morphologic, physiologic, and genetic properties allow them to colonize and multiply under the conditions that exist in particular sites, to coexist with other colonizing organisms, and to inhibit competing intruders. Thus, each accessible area of the body presents a particular ecologic niche, colonization of which requires a particular set of properties of the invading microbe. Organisms of the normal flora may have a symbiotic relationship that benefits the host or may simply live as commensals with a neutral relationship to the host. A parasitic relationship that injures the host would not be considered "normal," but in most instances not enough is known about the organism–host interactions to make such distinctions. Like houseguests, the members of the normal flora may stay for highly variable periods. Residents are strains that have an established niche at one of the many body sites, which they occupy indefinitely.
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