Factors Determining the Nature of the Normal Flora

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.