Skin flora - AbsoluteAstronomy.com

The skin flora are the microorganism

Microorganism

A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

s which reside on the skin. Most research has been upon those that reside upon the 2 square metres of human

Human

Humans are the only living species in the Homo genus...

skin. Many of them are bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

of which there are around 1000 species upon human skin from 19 phyla

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

. The total number of bacteria on an average human has been estimated at 10¹² (1,000,000,000,000). Most are found in the superficial layers of the epidermis and the upper parts of hair follicles.

Skin flora are usually non-pathogenic, and either commensals (are not harmful to their host) or mutualistic (offer a benefit). The benefits bacteria can offer include preventing transient pathogenic organisms from colonizing the skin surface, either by competing for nutrients, secreting chemicals against them, or stimulating the skin's immune system

Immune system

An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

. However, resident microbes can cause skin diseases and enter the blood system creating life-threatening diseases particularly in immunosuppressed people. Hygiene to control such flora is important in preventing the transmission of antibiotic resistant hospital-acquired infections.

A major nonhuman skin flora is Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis is a chytrid fungus that causes the disease chytridiomycosis. In the decade after it was first discovered in amphibians in 1998, the disease devastated amphibian populations around the world, in a global decline towards multiple extinctions, part of the Holocene...

, a chytrid and non-hyphal zoosporic fungus that causes chytridiomycosis

Chytridiomycosis

Chytridiomycosis is an infectious disease of amphibians, caused by the chytrid Batrachochytrium dendrobatidis, a non-hyphal zoosporic fungus. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species in western North America, Central America, South...

, an infectious disease thought to be responsible for the decline in amphibian populations

Decline in amphibian populations

Dramatic declines in amphibian populations, including population crashes and mass localized extinctions, have been noted since the 1980s from locations all over the world...

Bacteria

The estimate of the number of species present on skin bacteria has been radically changed by the use of 16S ribosomal RNA

16S ribosomal RNA

16S ribosomal RNA is a component of the 30S subunit of prokaryotic ribosomes. It is approximately 1.5kb in length...

to identify bacterial species present on skin samples direct from their genetic material. Previously such identification had depended upon microbiological culture

Microbiological culture

A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...

upon which many varieties of bacteria did not grow and so were hidden to science.

Staphylococcus epidermidis
Staphylococcus epidermidis
Staphylococcus epidermidis is one of thirty-three known species belonging to the genus Staphylococcus. It is part of human skin flora, and consequently part of human flora. It can also be found in the mucous membranes and in animals. Due to contamination, it is probably the most common species...

and Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

were thought from cultural based research to be dominant. However 16S ribosomal RNA

16S ribosomal RNA

16S ribosomal RNA is a component of the 30S subunit of prokaryotic ribosomes. It is approximately 1.5kb in length...

research finds that while common, these species make up only 5% of skin bacteria. However, skin variety provides a rich and diverse habitat for bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

. Most come from four phyla: Actinobacteria

Actinobacteria

Actinobacteria are a group of Gram-positive bacteria with high guanine and cytosine content. They can be terrestrial or aquatic. Actinobacteria is one of the dominant phyla of the bacteria....

(51.8%), Firmicutes

Firmicutes

The Firmicutes are a phylum of bacteria, most of which have Gram-positive cell wall structure. A few, however, such as Megasphaera, Pectinatus, Selenomonas and Zymophilus, have a porous pseudo-outer-membrane that causes them to stain Gram-negative...

(24.4%), Proteobacteria

Proteobacteria

The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....

(16.5%), and Bacteroidetes

Bacteroidetes

The phylum Bacteroidetes is composed of three large classes of bacteria that are widely distributed in the environment, including in soil, in sediments, sea water and in the guts and on the skin of animals....

(6.3%).

There are three main ecological areas: moist, dry and sebaceous. Propionibacteria and Staphylococci species were the main species in sebaceous areas. In moist places on the body Corynebacteria together with Staphylococci dominate. In dry areas, there is a mixture of species but b-Proteobacteria

Proteobacteria

The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....

and Flavobacteriales

Flavobacteriales

The order Flavobacteriales is composed of three families of environmental bacteria....

are dominant. Ecologically, sebaceous areas had greater species richness than moist and dry one. The areas with least similarity between people in species were the spaces between finger

Finger

A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....

s, the spaces between toe

Toe

Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being digitigrade. Humans, and other animals that walk on the soles of their feet, are described as being plantigrade; unguligrade animals are those that walk on hooves at the tips of...

s, axillae, and umbilical cord

Umbilical cord

In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...

stump. Most similarly were beside the nostril

Nostril

A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...

, nares (inside the nostril), and on the back.

Frequency of the best studied skin microbes
Organism	observations
Staphylococcus epidermidis Staphylococcus epidermidis Staphylococcus epidermidis is one of thirty-three known species belonging to the genus Staphylococcus. It is part of human skin flora, and consequently part of human flora. It can also be found in the mucous membranes and in animals. Due to contamination, it is probably the most common species...	Common, occasionally pathogenic
Staphylococcus aureus Staphylococcus aureus Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...	Infrequent, usually pathogenic
Staphylococcus warneri Staphylococcus warneri Staphylococcus warneri is a member of the bacterial genus Staphylococcus, consisting of Gram-positive bacteria with spherical cells appearing in clusters. It is coagulase-negative and is a common commensal organism found as part of the skin flora on humans and animals. Like other coagulase-negative...	Infrequent, occasionally pathogenic
Streptococcus pyogenes Streptococcus pyogenes Streptococcus pyogenes is a spherical, Gram-positive bacterium that is the cause of group A streptococcal infections. S. pyogenes displays streptococcal group A antigen on its cell wall. S...	Infrequent, usually pathogenic
Streptococcus mitis Streptococcus mitis Streptococcus mitis is a mesophilic alpha-hemolytic species of Streptococcus that inhabits the human mouth. It is a Gram positive, coccus, facultative anaerobe and catalase negative. It can cause endocarditis...	Frequent, occasionally pathogenic
Propionibacterium acnes Propionibacterium acnes Propionibacterium acnes is a relatively slow growing, typically aerotolerant anaerobic gram positive bacterium that is linked to the skin condition acne; it can also cause chronic blepharitis and endophthalmitis, the latter particularly following intraocular surgery...	Frequent, occasionally pathogenic
Corynebacterium Corynebacterium Corynebacterium is a genus of Gram-positive rod-shaped bacteria. They are widely distributed in nature and are mostly innocuous. Some are useful in industrial settings such as C. glutamicum. Others can cause human disease. C... spp.	Frequent, occasionally pathogenic
Acinetobacter johnsonii	Frequent, occasionally pathogenic
Pseudomonas aeruginosa Pseudomonas aeruginosa Pseudomonas aeruginosa is a common bacterium that can cause disease in animals, including humans. It is found in soil, water, skin flora, and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in hypoxic atmospheres, and has, thus, colonized many... >Infrequent, occasionally pathogenic

Fungal

A study of the area between toes in 100 young adults found 14 different genera of fungi. These include yeast

Yeast

Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

s such as Candida albicans
Candida albicans
Candida albicans is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans. Systemic fungal infections including those by C...

, Rhodotorula rubra
Rhodotorula
Rhodotorula is a pigmented yeast, part of the Basidiomycota phylum, quite easily identifiable by distinctive orange/red colonies when grown on SDA . This distinctive colour is the result of pigments that the yeast creates to block out certain wavelengths of light that would otherwise be damaging...

, Torulopsis and Trichosporon cutaneum, dermatophytes (skin living fungi) such as Microsporum gypseum, and Trichophyton rubrum
Trichophyton rubrum
Trichophyton rubrum is a fungus that is the most common cause of athlete's foot, jock itch and ringworm. This fungus was first described by Malmsten in 1845....

and nondermatophyte fungi (opportunistic fungi that can live in skin) such as Rhizopus stolonifer, Trichosporon cutaneum, Fusarium
Fusarium
Fusarium is a large genus of filamentous fungi widely distributed in soil and in association with plants. Most species are harmless saprobes, and are relatively abundant members of the soil microbial community. Some species produce mycotoxins in cereal crops that can affect human and animal health...

, Scopulariopsis brevicaulis, Curvularia
Curvularia
Curvularia is a hyphomycete fungus which is a facultative pathogen of many plant species and of the soil. Most Curvularia are found in tropical regions, though a few are found in temperate zones....

, Alternaria alternata
Alternaria alternata
Alternaria alternata has been recorded causing leaf spot and other diseases on over 380 host species. It is opportunistic pathogen on numerous hosts causing leaf spots, rots and blights on many plant parts...

, Paecilomyces
Paecilomyces
Paecilomyces is a genus of nematophagous fungus which kills harmful nematodes by pathogenesis, causing disease in the nematodes. Therefore the fungus can be used as a bio-nematicide to control nematodes by applying it to soil.-Species:...

, Aspergillus flavus
Aspergillus flavus
Aspergillus flavus is a fungus. It is a common mold in the environment, and can cause storage problems in stored grains. It can also be a human pathogen, associated with aspergillosis of the lungs and sometimes causing corneal, otomycotic, and nasoorbital infections. Many strains produce...

and Penicillium
Penicillium
Penicillium is a genus of ascomycetous fungi of major importance in the natural environment as well as food and drug production. Members of the genus produce penicillin, a molecule that is used as an antibiotic, which kills or stops the growth of certain kinds of bacteria inside the body...

species.

Relationship to host

Skin microflora can be commensals, mutualistic or pathogen

Pathogen

A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

s. Often they can be all three depending upon the strength of the person's immune system

Immune system

. Research upon the immune system in the gut

Gut (zoology)

In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...

and lungs has shown that microflora aids immunity development: however such research has only started upon whether this is the case with the skin. Pseudomonas aeruginosa
Pseudomonas aeruginosa
Pseudomonas aeruginosa is a common bacterium that can cause disease in animals, including humans. It is found in soil, water, skin flora, and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in hypoxic atmospheres, and has, thus, colonized many...

is an example of a mutualistic bacterium that can turn into a pathogen and cause disease: if it gains entry into the blood system it can result in infections in bone, joint, gastrointestinal, and respiratory systems. It can also cause dermatitis

Dermatitis

-Etymology:Dermatitis derives from Greek derma "skin" + -itis "inflammation" and genetic disorder.-Terminology:There are several different types of dermatitis. The different kinds usually have in common an allergic reaction to specific allergens. The term may describe eczema, which is also called...

. However, Pseudomonas aeruginosa produces antimicrobial substances such as pseudomonic acid that are exploited commercially such as Mupirocin

Mupirocin

Mupirocin is an antibiotic originally isolated from Pseudomonas fluorescens NCIMB 10586, developed by Beecham....

. This works against staphylococcal and streptococcal infections. Pseudomonas aeruginosa also produces substances that inhibit the growth of fungus

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

species such as Candida krusei
Candida krusei
Candida krusei is a budding yeast involved in chocolate production. Candida krusei is an emerging fungal nosocomial pathogen primarily found in the immunocompromised and those with hematological malignancies. It has natural resistance to fluconazole, a standard antifungal agent...

, Candida albicans
Candida albicans
Candida albicans is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans. Systemic fungal infections including those by C...

, Torulopsis glabrata, Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...

and Aspergillus fumigatus
Aspergillus fumigatus
Aspergillus fumigatus is a fungus of the genus Aspergillus, and is one of the most common Aspergillus species to cause disease in individuals with an immunodeficiency....

. It can also inhibit the growth of Helicobacter pylori
Helicobacter pylori
Helicobacter pylori , previously named Campylobacter pyloridis, is a Gram-negative, microaerophilic bacterium found in the stomach. It was identified in 1982 by Barry Marshall and Robin Warren, who found that it was present in patients with chronic gastritis and gastric ulcers, conditions that were...

. So important is its antimicrobial actions that it has been noted that "removing P. aeruginosa from the skin, through use of oral or topical antibiotics, may inversely allow for aberrant yeast colonization and infection."

Another aspect of bacteria is the generation of body odor

Body odor

Body odor or body odour, sometimes colloquially abbreviated as B.O., is the smell of bacteria growing on the body. The bacteria multiply rapidly in the presence of sweat, but sweat itself is almost completely odorless to humans....

. Sweat

SWEAT

SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...

is odorless but Propionibacteria in adolescent and adult sebaceous glands can turn its amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s into propionic acid

Propionic acid

Propanoic acid is a naturally occurring carboxylic acid with chemical formula CH3CH2COOH. It is a clear liquid with a pungent odor...

. Staphylococcus epidermidis
Staphylococcus epidermidis
Staphylococcus epidermidis is one of thirty-three known species belonging to the genus Staphylococcus. It is part of human skin flora, and consequently part of human flora. It can also be found in the mucous membranes and in animals. Due to contamination, it is probably the most common species...

create the other source of body odor: isovaleric acid (3-methyl butanoic acid). In addition to these, strong foot odor is due to Bacillus subtilis
Bacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...

.

Antimicrobial peptides

The skin creates antimicrobial peptides

Antimicrobial peptides

Antimicrobial peptides are an evolutionarily conserved component of the innate immune response and are found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for antimicrobial peptides...

such as cathelicidin

Cathelicidin

Members of the cathelicidin family of antimicrobial polypeptides are characterized by a highly conserved region and a highly variable cathelicidin peptide domain.Cathelicidin peptides have been isolated from many different species of mammals...

s that control the proliferation of skin microbes. Cathelicidins not only reduce microbe numbers directly but also cause the secretion of cytokine

Cytokine

Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...

release which induces inflammation

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

, angiogenesis

Angiogenesis

Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...

, and reepithelialization. Conditions such as atopic dermatitis

Atopic dermatitis

Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...

have been linked to the suppression in cathelicidin production. In rosacea

Rosacea

Rosacea is a chronic condition characterized by facial erythema . Pimples are sometimes included as part of the definition. Unless it affects the eyes, it is typically a harmless cosmetic condition...

abnormal processing of cathelicidin cause inflammation. Psoriasis

Psoriasis

Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...

has been linked to self-DNA created from cathelicidin peptides that causes autoinflammation

Autoimmunity

Autoimmunity is the failure of an organism to recognize its own constituent parts as self, which allows an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease...

. A major factor controlling cathelicidin is vitamin D₃.

Acidity

The superficial layers of the skin are naturally acidic (pH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

4-4.5) due to lactic acid in sweat

SWEAT

and produced by skin bacteria. At this pH mutualistic flora such as Staphylococci, Micrococci, Corynebacterium
Corynebacterium
Corynebacterium is a genus of Gram-positive rod-shaped bacteria. They are widely distributed in nature and are mostly innocuous. Some are useful in industrial settings such as C. glutamicum. Others can cause human disease. C...

and Propionibacteria grow but not transient bacteria such as Gram negative bacteria like Escherichia
Escherichia
Escherichia is a genus of Gram-negative, non-spore forming, facultatively anaerobic, rod-shaped bacteria from the family Enterobacteriaceae. In those species which are inhabitants of the gastrointestinal tracts of warm-blooded animals, Escherichia species provide a portion of the...

and Pseudomonas
Pseudomonas
Pseudomonas is a genus of gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. As a result, the genus Pseudomonas includes strains formerly classified in the...

or Gram positive ones such as Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

or Candida albicans
Candida albicans
Candida albicans is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans. Systemic fungal infections including those by C...

. Another factor effecting the growth of pathological bacteria is that the antimicrobial substances secreted by the skin are enhanced in acidic conditions. In alkaline conditions, bacteria cease to be attached to the skin and are more readily shed. It has been observed that the skin also swells under alkaline conditions and opens up allowing move to the surface.

Immune system

If activated, the immune system

Immune system

in the skin produces cell-mediated immunity

Cell-mediated immunity

Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells , antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen...

against microbes such as dermatophyte

Dermatophyte

Dermatophytes are a common label for a group of three types of fungus that commonly causes skin disease in animals and humans. These anamorphic genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera...

s (skin fungi). One reaction is to increase stratum corneum

Stratum corneum

The stratum corneum is the outermost layer of the epidermis, consisting of dead cells that lack nuclei and organelles. The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress...

turnover and so shed the fungus from the skin surface. Skin fungi such as Trichophyton rubrum
Trichophyton rubrum
Trichophyton rubrum is a fungus that is the most common cause of athlete's foot, jock itch and ringworm. This fungus was first described by Malmsten in 1845....

have evolved to create substances that limit the immune response to them. The shedding of skin is a general means to control the build up flora upon the skin surface.

Skin diseases

Microorganisms play a role in noninfectious skin diseases such as atopic dermatitis

Atopic dermatitis

Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...

, rosacea

Rosacea

, psoriasis

Psoriasis

, and acne

Acne

Acne is a general term used for acneiform eruptions. It is usually used as a synonym for acne vulgaris, but may also refer to:*Acne aestivalis*Acne conglobata*Acne cosmetica*Acne fulminans*Acne keloidalis nuchae*Acne mechanica...

Damaged skin can cause nonpathogenic bacteria to become pathogenic.

Contagion

Skin flora do not readily pass between people: 30 seconds of moderate friction and dry hand contact results in a transfer of only 0.07% of natural hand flora from naked with a greater percentage from gloves.

Removal

The most effective (60 to 80% reduction) antimicrobial washing is with ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

, isopropanol, and n-propanol. Viruses are most affected by high (95%) concentrations of ethanol, while bacteria are more affected by n-propanol.

Unmedicated soaps are not very effective as illustrated by the following data. Health care workers washed their hands once in nonmedicated liquid soap for 30 seconds. The students/technicians for 20 times.

Skin flora upon two hospital groups in colony-forming units per mL
L
Ł or ł, described in English as L with stroke, is a letter of the Polish, Kashubian, Sorbian, Łacinka , Łatynka , Wilamowicean, Navajo, Dene Suline, Inupiaq, Zuni, Hupa, and Dogrib alphabets, several proposed alphabets for the Venetian language, and the ISO 11940 romanization of the Thai alphabet...

.
group and hand skin condition	unwashed	washed
Health care workers healthy	3.47	3.15
Health care workers damaged	3.33	3.29
Students/technicians healthy	4.39	3.54
Students/technicians damaged	4.58	4.43

An important use of hand washing

Hand washing

Hand washing for hand hygiene is the act of cleaning the hands with or without the use of water or another liquid, or with the use of soap, for the purpose of removing soil, dirt, and/or microorganisms....

is to prevent the transmission of antibiotic resistant skin flora that cause hospital-acquired infections such as Methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus is a bacterium responsible for several difficult-to-treat infections in humans. It is also called multidrug-resistant Staphylococcus aureus and oxacillin-resistant Staphylococcus aureus...

. While such flora have become antibiotic resistant due to antibiotics there is no evidence that recommended antiseptics or disinfectants selects for antibiotic-resistant organisms when used in hand washing. However, many strains of organisms are resistant to some of the substances used in antibacterial soaps such as Triclosan

Triclosan

Triclosan is an antibacterial and antifungal agent. It is a polychloro phenoxy phenol. Despite being used in many consumer products, beyond its use in toothpaste to prevent gingivitis, there is no evidence according to the American Food and Drug Administration that triclosan provides an extra...

.

One survey of bar soaps

Soap

In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...

in dentist clinics found they all had their own flora and on average from two to five different genera of microorganisms with those used most more likely to have more species varieties. Another survey of bar soaps in public toilets found even more flora. Another study found that very dry soaps are not infected while all are that rest in pools of water. However, research upon soap that was specially infected found that soap flora do not transmit to the hands.

Damaged skin

Washing skin repeatedly can damage the protective external layer and cause transepidermal loss of water. This can be seen in roughness characterized by scaling and dryness, itchiness, dermatitis

Dermatitis

provoked by microorganisms and allergen

Allergen

An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....

s penetrating the corneal layer and redness. Wearing gloves can cause further problems since it produces a humid environment favoring the growth of microbes and also contains irritants such as latex

Latex

Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...

and talcum powder.

Hand washing can damage skin because the stratum corneum

Stratum corneum

top layer of skin consists of 15 to 20 layers of keratin

Keratin

Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

disks, corneocytes, each of which is each surrounded by a thin film of skin lipid

Lipid

Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

s which can be removed by alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s and detergent

Detergent

A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...

s.

Damaged skin defined by extensive cracking of skin surface, widespread reddening or occasional bleeding has also been found to be more frequently colonized by Staphylococcus hominis
Staphylococcus hominis
Staphylococcus hominis is a coagulase-negative member of the bacterial genus Staphylococcus, consisting of Gram positive, spherical cells in clusters. It occurs very commonly as a harmless commensal on human and animal skin. However, like many other coagulase-negative staphylococci, S...

and these were more likely to methicillin

Methicillin

Meticillin or methicillin is a narrow-spectrum beta-lactam antibiotic of the penicillin class. It should not be confused with the antibiotic metacycline.-History:Methicillin was developed by Beecham in 1959...

resistant. Though not related to greater antibiotic resistance, damaged skin was also more like to be colonized by Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

, gram-negative bacteria, Enterococci and Candida
Candida (genus)
Candida is a genus of yeasts. Many species are harmless commensals or endosymbionts of animal hosts including humans, but other species, or harmless species in the wrong location, can cause disease. Candida albicans can cause infections in humans and other animals, especially in immunocompromised...

.

Comparison with other flora

The skin flora is different from that of the gut which is predominately Firmicutes

Firmicutes

and Bacteroidetes

Bacteroidetes

. There is also low level of variation between people that is not found in gut studies. Both gut and skin flora however lack the diversity found in soil flora.

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Bacteria

Fungal

Relationship to host

Antimicrobial peptides

Acidity

Immune system

Skin diseases

Contagion

Removal

Damaged skin

Comparison with other flora

See also

External links