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FACTORS DETERMINING THE NATURE OF THE NORMAL FLORA
Local physiologic and ecologic conditions determine the nature of the flora. These conditions are sometimes highly complex, differing from site to site, and sometimes vary with age. Conditions include the amounts and types of nutrients available, pH, oxidation –reduction potentials, and resistance to local antibacterial substances such as bile and lysozyme. Many bacteria have adhesin-mediated affinity for receptors on specific types of epithelial cells, which facilitates colonization and multiplication while avoiding removal by the flushing effects of surface fluids and peristalsis. Various microbial interactions also determine their relative prevalence in the flora. These interactions include competition for nutrients, inhibition by the metabolic products of other organisms (eg, by hydrogen peroxide or volatile fatty acids), and production of antibiotics and bacteriocins.
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