ABSTRACT
The human mucous and epithelial surfaces are colonized with aerobic and anaerobic
microorganisms (1). These surfaces are the skin, conjunctiva, mouth, nose, throat, lower
intestinal tract, vagina, and the urethra. The trachea, bronchi, esophagus, stomach, and
upper urinary tract are not normally colonized by indigenous flora. However, a limited
number of transient organisms may by present at these locations. Differences in the environ-
ment, such as oxygen tension and pH and variations in bacterial adherence, account for the
changing patterns of bacterial colonization. The microflora also varies within the different
body sites; in the oral cavity, for example, the organisms in the buccal folds vary in their
concentration and types from those from the tongue or gingival sulci. However, the bacteria
that prevail in a system generally belong to certain major bacterial species. The relative
and total bacterial counts can be influenced by various factors, such as age, diet, anatomic
variations, illness, hospitalization, and antimicrobial therapy.
