The human skin is relentlessly and endlessly showered by organisms present in the environment. Even though the flora include some fungi and protists, bacteria are the predominant ones and seen in numerous numbers. Depending on a person’s hygienic condition, the contamination by his own secretions and excretions varies. The normal flora depends on the body area, type of clothes the person wears, job type and the surroundings in which he/she lives.
Commonly demonstrated flora include; Diphtheroids, Staphylococci, E. coli, Candida albicans, etc. Face, neck, hands and buttocks bears Staphylococci and hemolytic Streptococci. Hair harbors Staphylococcus aureus. Malassezia is a common kind of yeast that is seen on the human skin.
The normal flora can be saprophytes, commensals, facultative and true pathogens. The flora remains constant for a particular species. The flora can be transients and residents. The transients vary from time to time and are not permanent. But the residents are always a common population and can’t be removed permanently. These residents prevent colonization of the body by other organisms.
The normal flora can become pathogenic when host’s defense mechanism is lowered. Their abnormal multiplication causes disease conditions such as enteritis and endotoxic shock. The mineral content of the enamel of the teeth is degraded by the acid by-products secreted by the bacteria after fermentation which leads to dental caries. Certain Streptococci present in the mouth are responsible for dental caries. Subsequently the protein matrix is also digested.
The intestinal areas of the newborn infants are found to be sterile; but some carry few microbes acquired during birth. In breast feeding children, the intestine contains Lactobacillus, colon bacilli and Staphylococci. As the baby grows into an adult, the flora also changes with the diet. In the adut, there are approximately 10³-10⁶ bacteria/gm of content in the duodenum.
Even our conjunctiva, stomach, nasopharynx, upper respiratory tract and genitourinary tract also bear a normal flora of microbes. The dominating microbes in the eye region are Diphtheroids, Staphylococci, etc. The nasal flora is mostly responsible for nose, throat and lung infections. The mouth carries Micrococcus, Bacillus, Coli forms, Proteus and Lactobacillus. Even Candida has been reported in some individuals. The gum pocket bears Streptococci, Vibrio, Mycoplasma, Neisseria, etc. Our stomach has got a high acidic condition, but still there certain bacteria which can withstand those conditions also. Streptococcus, Staphylococcus, Lactobacillus, etc are seen as normal flora. Helicobacter pylori are inhabitants of the stomach walls, but at times it become pathogenic and causes ulcers and at times even become responsible for gastric cancer.
Normal men and women carry Mycobacterium smegmatis in their genital region. Female urethra, sometimes carries gram positive cocci. Healthy men carry alpha- hemolytic Streptococci, Ureaplasma urealyticum, Lactobacillus, etc. The nature of the vaginal flora depends upon the enzyme content of the vaginal region and the pH of the vaginal secretions. During pregnancy; Staphylococcus epidermidis, Doderlien’s bacilli (Lactobacillus) and yeasts increase in number.
Depending upon the body’s needs, vitamin K and vitamin B are synthesized by the intestinal microbial flora. Some of the normal flora produce certain antibiotic substances such as colicins, which affect adversely on the pathogens. These organisms only when isolated for more than once from blood cultures become significant and should be considered dangerous.