ABSTRACT
The human body’s mucosal and epithelial surfaces are covered with aerobic and anaerobic micro-organisms.1 The surfaces of the body that are inhabited by normal flora are the skin, conjunctiva, mouth, nose, throat, lower intestinal tract, vagina, and urethra. The organisms that reside at these sites are predominantly anaerobic and are actively multiplying. 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 sites from time to time. Differences in the environment, such as oxygen tension and pH and variations in the ability of bacteria to adhere to these surfaces, account for changing patterns of colonization. Microflora also vary in different sites within the body system, as in the oral cavity; for example, the micro-organisms present in the buccal folds vary in their concentration and types of strains from those isolated from the tongue or gingival sulci. However, the organisms that prevail in one body system tend to belong to certain major bacterial species, and their presence in that system is predictable. The relative and total counts of organisms can be affected by various factors, such as age, diet, anatomic variations, illness, hospitalization, and antimicrobial therapy. However, these sets of bacterial flora, with predictable pattern, remain stable through life, despite their subjection to perturbing factors.
