Lecture Notes 4.26

Lecture Notes 4.26 - Notes 4/2610 Microbial Interactions...

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Notes – 4/2610 Microbial Interactions with Humans I. Beneficial Microbial Interactions with Humans 28.1 Overview of Human-Microbial Interactions o Most microbes are benign 0. A few contribute directly to human health and even fewer pose direct threats to health o Normal Microbial Flora 1. Microbes usually found associated with human body tissue o Humans are colonized by microbes at birth o Pathogens 2. Microbial parasites o Pathogenicity 3. The ability of a parasite to inflict damage on the host o Virulence 4. The quantitative measure of pathogenicity o Opportunistic Pathogen 5. Causes disease only in the absence of normal host resistance 0. Infection Situation in which a microbe is established and growing in a host, whether or not the host is harmed 1. Disease Damage or injury to the host that impairs host function o Animals provide a favorable environment for the growth of many microbes o Infections frequently begin at sites in the animal’s mucous membranes 28.2 Normal Microbial Flora of the Skin o Skin generally a dry, acid environment -does not support the growth of most microbes o Most areas (e.g., sweat glands) readily colonized by gram-positive bacteria and other normal flora of the skin 2. The Skin Microflora Composition is influenced by 6. Environmental factors (e.g., weather) 7. Host factors (e.g., age, personal hygiene) 28.3 Normal Microbial Flora of the Oral Cavity o The oral cavity is a complex, heterogeneous microbial habitat o Saliva contains antimicrobial enzymes 8. But high concentrations of nutrients near surfaces in the mouth promote localized microbial growth o Tooth consists of a mineral matrix (enamel) surrounding living tissue (dentin and pulp) o Bacteria colonize tooth surfaces by first attaching to acidic glycoproteins deposited there by saliva
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o Extensive growth of oral microbes, especially streptococci, results in a thick bacterial layer (dental plaque) o As plaque continues to develop, anaerobic bacterial species begin to grow o As dental plaque accumulates, the microbes produce high concentrations of acid that results in decalcification of the tooth enamel (dental caries) o The lactic acid bacteria Streptococcus sobrinus and S. mutans are common agents in dental caries 28.4 Normal Microbial Flora of the Gastrointestinal Tract 3.
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