Human Genomic Project and The Roles of Normal Flora

More about normal flora

The term or the word “normal microbial flora” denotes the population of microorganisms that inhabit and may multiply the skin and mucous membranes of healthy normal persons. Th e microorganisms that live inside and on humans (now referred to as the normal microbiota ) are estimated to outnumber human somatic and germ cells by a factor of ten. Th e loci of the above microbial symbionts are collectively defined as the microbiome .

Recent searches have proved that the “ normal microbiota ” provides

the first line or the primary mechanism of defense against microbial pathogens, assist in digestion, play a role in toxin degradation,the assimilation and contribute to the development and maturation of the immune system. Shifts and replaces with the normal microbiota or stimulation of inflammation by these commensals may cause diseases such as inflammatory bowel disease.

Human microbiome project

In a broad attempt to understand the role played by resident microbial ecosystems in human health and disease, in 2007, the National Institutes of Health launched the Human Microbiome Project. One of the main goals of this project is to understand the range of human genetic and physiologic diversity with the understandings and findings , the microbiome, and the factors that influence the distribution and evolution of the constituent microorganisms.

One aspect of this project involves having several research groups simultaneously embark and studies upon surveying the microbial communities on human skin and in mucosal areas such as the mouth, esophagus, stomach, colon, and vagina using small-subunit (16S) ribosomal RNA gene sequencing. Among the questions that will be addressed by this project are How stable and the determinant is an individual’s microbiota throughout one day and during their respective lifespan? How similar are the microbiomes or the flora between members of a family or niche or members of a community or across communities in different environments? Do all humans can possess an identifiable “core” or similar microbiome, and if so, how is it acquired and transmitted? What factors acts the genetic diversity of the microbiome, and how does this diversity affect adaptation and habitat by the microorganisms and the host to markedly different lifestyles and habitat. and to various physiological or pathophysiological and other various states? Numerous observations have already been made. For example, it has been determined that there are large differences among individuals in terms of the numbers and types of species of microorganisms inhabiting the colon and that obesity may be correlated with the types of microbes involved in specific c metabolic pathways in the gastrointestinal tract. Readers should be aware that this field is rapidly evolving, and our understanding of the human microbiota will necessarily change as more information about resident microbial communities becomes available through the Human Microbiome Project.

Role of resident microbial flora

The skin and mucous membranes always possess a variety of microorganisms that can be arranged into two groups:

(1) the resident microbiota consists of relatively fixed types of microorganisms regularly found in a given environment at a given age; if disturbed and altered, it promptly reestablishes itself; and

(2) transient microbiota consists of nonpathogenic or probably pathogenic microorganisms that inhabit the skin and mucous membranes for hours, days, or weeks. This group of the microbiota is derived from our environment, does not produce disease or are nonpathogenic , and does not establish itself permanently,ie is temporary on the surface. Members of the transient microbiota are generally of little significance ,less likely important so long as the normal resident flora remains intact. However, if the resident microbiota is disturbed, transient microorganisms may colonize, proliferate, multiply and produce disease with infection.It is likely that microorganisms that can be cultured in the laboratory define only a fraction of those that are bodies of the normal resident or transient microorganisms. When the broad-range polymerase chain reaction (PCR) is used amplify bacterial 16S rDNA, many previously unidentified ed bacteria can be detected, as in secretions from patients with bacterial vaginosis. Th e maximum number of species that make up the normal microbiota has been shown to be much greater efficiency than previously recognized. Thus, the understanding and our knowledge of normal microbiota are in transition. As already mentioned, the relationship of previously unidentified and unknown microorganisms, which are potentially part of the normal microbiota, to disease is likely to change. The microorganisms that are constantly and regularly present on body surfaces are commensals. Their flourishing or multiplication in a given niche depends on physiologic factors of temperature, moisture, and the presence of certain nutrients and inhibitory substances. Their presence is not essential or necessary to live because “germ-free” animals can be reared in the complete absence of a normal microbiota. Yet the resident flora of certain areas plays a definite role in maintaining health and normal function. Members of the resident microbiota in the intestinal tract synthesize vitamin K and aid in the absorption and digestion of nutrients. On the mucous membranes and skin, the resident microbiota may prevent colonization by pathogens and possible infection through “bacterial interference interference.” The mechanism of bacterial interference may involve competition for receptors or on host cells, competition for nutrients, mutual inhibition or killing by metabolic with toxic products, mutual destruction by antibiotic materials or bacteriocins and other toxins , or other mechanisms. Suppression of the normal microbiota clearly creates a partial local space that tends to be filled by organisms from the environment or from any other parts of the body. Such microbiota behaves and serves as opportunists and may become pathogens. On the other hand, members of the normal microbiota may themselves produce disease under certain circumstances. These organisms are adapted to a noninvasive mode of life defined by the limitations of the environment. If forcefully removed from the restrictions of that environment may become pathogenic. For example, streptococci of the viridian group are the most common resident normal microbes of the upper respiratory tract. If large numbers of them are introduced into the bloodstream (eg, after tooth extraction or oral surgery), they may settle on deformed or prosthetic heart valves and produce infective and vigorous endocarditis. few in numbers occur transiently in the bloodstream with minor trauma or with similar infections.

(eg, dental scaling or vigorous brushing). Bacteroides species are the most common residential inhabiting bacteria of the large intestine are quite harmless in that location. However, if introduced into the 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 the normal resident microbiota is 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.

Normal Bacterial Microbiota:

Skin

Staphylococcus epidermis

Staphylococcus aureus (in small numbers)
Micrococcus species
α-Hemolytic and nonhemolytic streptococci (eg, Streptococcus mitis)
Corynebacterium species
Propionibacterium species
Peptostreptococcus species
Acinetobacter species
Small numbers of other organisms (Candida species, Pseudomonas aeruginous , etc)

Nasopharynx

Any amount of the following: diphtheroid , nonpathogenic Neisseria species, α-hemolytic streptococci; S epidermis diphtheroid , nonpathogenic Neisseria species, α-hemolytic streptococci; S epidermis , nonhemolytic streptococci, anaerobes (too many species to a list; varying amounts of Prevotella species, anaerobic cocci, Fusobacterium species, etc) Lesser amounts of the following when accompanied by organisms listed above yeasts, Haemophilus species, pneumococci, S aureus,gram-negative rods, Neisseria meningitides

Gastrointestinal tract and rectum

Various Enterobacteriaceae except Salmonella, Shigella, Yersinia, Vibrio, and Campylobacter species
Glucose non-fermenting gram-negative rods
Enterococci α-Hemolytic and nonhemolytic streptococci
Diphtheroids
Staphylococcus aureus in small numbers
Yeasts in small numbers
Anaerobes in large numbers (too many species to list)

Genitalia
Any amount of the following: Corynebacterium species, Lactobacillus species, α-hemolytic and nonhemolytic streptococci, nonpathogenic
Neisseria species
The following when mixed and not predominant: enterococci, Enterobacteriaceae and other gram-negative rods, Staphylococcus epidermis
Candida albicans, and other yeasts
Anaerobes (too many to list); the following may be important when in pure growth or clearly predominant: Prevotella, Clostridium

References:

D greenwood, Slack RCB and J Peutherer.Medical microbiology.

JG College, AG Fraser and BP Marmion.Practical Medical microbiology.Fourteenth Edition. Churchill Livingstone, 1996.

JP Micheal, ECS Chan and NR Krieg.Fifth Edition. Delhi: Mcgraw-hill, 1993.

M Cheesbrugh.Medical laboratory manual for tropical countries.London, 2007.