Monday, September 21, 2015

Normal flora of the human body (Part one)

normal flora of the human body

In a healthy human being, the internal tissues, e.g. blood, brain, muscle, etc., are normally free of microorganisms. However, the surface tissues, i.e., skin and mucous membranes, are constantly in contact with environmental organisms and become readily colonized by various microbial species. The mixture of organisms regularly found at any anatomical site is referred to as the normal flora.
The normal flora of humans consists of a few eukaryotic fungi and protists, but bacteria are the most numerous and obvious microbial components of the normal flora. A healthy foetus in utero is free from microorganisms. During birth the infant is exposed to vaginal flora. Within a few hours of birth oral and nasopharyngeal flora develops and in a day or two resident flora of the lower intestine appears.

Objectives of this review

Now let us look at some attainable objectives the audience or the reader of this post is expected to achieve at the end of successfully going through this review, they are as follows:
After a successful reading, you are expected to be able to:

1.      describe normal flora
2.      enlist the advantages and disadvantages of the flora
3.      describe the normal flora of various parts of the body

Normal Microbial flora

The term “normal microbial flora” denotes the population of microorganisms that inhabit the skin and mucous membranes of healthy, normal people. The skin and mucous membranes always harbour a variety of microorganisms that can be arranged into two groups:

1.      The resident flora consists of relatively fixed types of microorganisms regularly found in a given area at a given age; if disturbed, it promptly re-establishes itself.

2.      The transient flora consists of non-pathogenic or potentially pathogenic microorganisms that inhabit the skin or mucous membranes for hours, days, or weeks; it is derived from the environment, does not produce disease, and does not establish itself permanently on the surface. Members of the transient flora are generally of little significance so long as the normal resident flora remains intact. However, if the resident flora is disturbed, transient microorganisms may colonize, proliferate, and produce disease.

Resident flora

It consists of organisms which are regularly present in a particular area and when disturbed it re-establishes itself like Escherichia coli is a normal inhabitant of the intestine.

Role of resident flora

Microorganisms that are constantly present on body surfaces are commensals. Their growth in a given area depends upon physiologic factors like temperature, moisture, and the presence of certain nutrients and inhibitory substances. Resident flora of certain areas plays a definite role in maintaining health and normal function. Members of the resident flora in the intestinal tract synthesize vitamin K and aid in the absorption of nutrients. On mucous membranes and
skin, the resident flora may prevent colonization by pathogens and possible disease through “bacterial interference.” The mechanism of bacterial interference is not clear. It may involve competition for receptors or binding sites on host cells, competition for nutrients, mutual inhibition by metabolic or toxic products, mutual inhibition by antibiotic materials or bacteriocins, or other mechanisms. Suppression of the normal flora tends to be filled by organisms from the environment or from other parts of the body and such organisms behave as opportunists and may become pathogens. On the other hand, members of the normal flora may themselves produce disease under certain circumstances and if removed from the restrictions of that environment and introduced into the bloodstream or tissues, these organisms may become pathogenic. For example, streptococci of the viridans group are the
most common resident organisms of the upper respiratory tract and if large numbers of them are introduced into the bloodstream (eg, following tooth extraction or tonsillectomy), they may settle on deformed or prosthetic heart valves and produce infective endocarditis. Small numbers occur transiently in the bloodstream with minor trauma (eg, dental scaling or vigorous brushing). Bacteroides species are the commonest resident bacteria, if introduced into the free peritoneal cavity or into pelvic tissues along with other bacteria as a result of trauma, they cause suppuration and bacteremia. There are many other examples, but the important point is that microbes of the normal resident flora are harmless and may be beneficial in their normal location in the host and in the absence of coincident abnormalities. They may produce disease if introduced into foreign locations in large numbers and if predisposing factors are present.

It has both advantages as well as disadvantages, which we will commence its discussion in Part two of this post. So keep in touch for the part two.



A Medical Microbiologist, Public health worker, blogger and artcle writer, and offcourse a fan of Manchester United football club