Microbiota

• normal microbial flora denotes the population of microorganisms that inhabit the skin and mucous membranes of healthy normal persons
• The 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 10. Th e genomes of these microbial symbionts are collectively defined as the microbiome
• Research has shown that the “ normal microbiota ” provides a first line of defense against microbial pathogens, assist in digestion, play a role in toxin degradation, and contribute to maturation of the immune system.
• resident microbiota consists of relatively fixed types of microorganisms regularly found in a given area at a given age; if disturbed, it promptly reestablishes itself
• transient microbiota consists of nonpathogenic or potentially pathogenic microorganisms that inhabit the skin or mucous membranes for hours, days, or weeks
• transient microbiota is derived from the environment, does not produce disease, and does not establish itself permanently on the surface
• 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, the microbiome, and the factors that infl uence the distribution and evolution of the constituent microorganisms
• One aspect of Human Microbiome Project involves having several research groups simultaneously embark 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
• The predominant resident microorganisms of the skin are aerobic and anaerobic diphtheroid bacilli (eg, Corynebacterium, Propionibacterium); nonhemolytic aerobic and anaerobic staphylococci (Staphylococcus epidermidis and other coagulase-negative staphylococci, occasionally Staphylococcus aureus, and Peptostreptococcus species); gram-positive, aerobic, spore-forming bacilli that are ubiquitous in air, water, and soil; α-hemolytic streptococci (viridans streptococci) and enterococci (Enterococcus species); and gram-negative coliform bacilli and Acinetobacter
• Among the factors that may be important in eliminating nonresident microorganisms from the skin are the low pH, the fatty acids in sebaceous secretions, and the presence of lysozyme.