''Staphylococcus epidermidis'' is a
Gram-positive
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
The Gram stain is ...
bacterium, and one of over 40
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
belonging to the genus ''
Staphylococcus
''Staphylococcus'', from Ancient Greek σταφυλή (''staphulḗ''), meaning "bunch of grapes", and (''kókkos''), meaning "kernel" or " Kermes", is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillale ...
''.
It is part of the
normal human microbiota, typically the
skin microbiota, and less commonly the mucosal microbiota and also found in marine sponges.
It is a facultative
anaerobic bacteria
An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenat ...
. Although ''S. epidermidis'' is not usually
pathogenic
In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
The term ...
, patients with compromised
immune system
The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...
s are at risk of developing infection. These infections are generally
hospital-acquired.
''S. epidermidis'' is a particular concern for people with
catheters
In medicine, a catheter ( ) is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. Catheters are man ...
or other surgical implants because it is known to form
biofilms
A biofilm is a syntrophic community of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymer ...
that grow on these devices.
Being part of the normal skin microbiota, ''S. epidermidis'' is a frequent contaminant of specimens sent to the diagnostic laboratory.
Some strains of ''S. epidermidis'' are highly salt tolerant and commonly found in marine environments.
S.I. Paul et al. (2021)
isolated and identified salt tolerant strains of ''S. epidermidis'' (strain
ISP111AISP111Ban
ISP111C from ''
Cliona viridis'' sponges of the
Saint Martin's Island Area of the
Bay of Bengal
The Bay of Bengal is the northeastern part of the Indian Ocean. Geographically it is positioned between the Indian subcontinent and the Mainland Southeast Asia, Indochinese peninsula, located below the Bengal region.
Many South Asian and Southe ...
,
Bangladesh
Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...
.
Commensal ''S. epidermidis'' is an essential part of a healthy
skin microbiota. It contributes through supporting a healthy skin barrier, healing cuts of the skin, protecting the skin microbiota from colonization of skin pathogens, and acting as an immune system modulator.
Etymology
'Staphylococcus' - bunch of grape-like berries, 'epidermidis' - of the epidermis.
Discovery
Friedrich Julius Rosenbach
Friedrich Julius Rosenbach, also known as Anton Julius Friedrich Rosenbach, (16 December 1842 – 6 December 1923) was a German physician and microbiologist. He is credited for differentiating ''Staphylococcus aureus'' and ''Staphylococcus albus' ...
distinguished ''S. epidermidis'' from ''S. aureus'' in 1884, initially naming ''S. epidermidis'' as ''S. albus''. He chose ''aureus'' and ''albus'' since the bacteria formed yellow and white colonies, respectively.
Microbiology

''Staphylococcus epidermidis'' is a very hardy microorganism, consisting of nonmotile,
Gram-positive
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
The Gram stain is ...
cocci, arranged in grape-like clusters. It forms white, raised, cohesive colonies about 1–2 mm in diameter after overnight incubation, and is not
hemolytic
Hemolysis or haemolysis (), also known by several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in vivo ...
on blood agar.
It is a
catalase
Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting ...
-positive,
coagulase
Coagulase is a protein enzyme produced by several microorganisms that enables the conversion of fibrinogen to fibrin. In the laboratory, it is used to distinguish between different types of ''Staphylococcus'' isolates. Importantly, '' S. aureus' ...
-negative,
facultative anaerobe
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...
that can grow by
aerobic respiration
Cellular respiration is the process of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cellu ...
or by
fermentation
Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...
. Some strains may not ferment.
Biochemical tests indicate this microorganism also carries out a weakly positive reaction to the
nitrate reductase test
The nitrate reductase test is a test to differentiate between bacteria based on their ability or inability to reduce nitrate (NO3−) to nitrite (NO2−) using anaerobic respiration.
Procedure
Various assays for detecting nitrate reduction have be ...
. It is positive for
urease
Ureases (), functionally, belong to the superfamily of amidohydrolases and phosphotriesterases. Ureases are found in numerous Bacteria, Archaea, fungi, algae, plants, and some invertebrates. Ureases are nickel-containing metalloenzymes of high ...
production, is oxidase negative, and can use glucose, sucrose, and lactose to form acid products. In the presence of lactose, it will also produce gas. Nonpathogenic ''S. epidermidis'' unlike pathogenic ''S. aureus'' does not possess the
gelatinase enzyme, so it cannot hydrolyze gelatin. It is sensitive to
novobiocin
Novobiocin, also known as albamycin, is an aminocoumarin antibiotic that is produced by the actinomycete ''Streptomyces niveus'', which has recently been identified as a subjective synonym for ''S. spheroides'' a member of the class Actinomycet ...
, providing an important test to distinguish it from ''
Staphylococcus saprophyticus
''Staphylococcus saprophyticus'' is a Gram-positive coccus belonging to the genus ''Staphylococcus''. ''S. saprophyticus'' is a common cause of community-acquired urinary tract infections.
History
''Staphylococcus saprophyticus'' was not recogni ...
'', which is coagulase-negative, as well, but novobiocin-resistant.
Similar to those of ''S. aureus'', the cell walls of ''S. epidermidis'' have a transferrin-binding protein that helps the organism obtain iron from
transferrin
Transferrins are glycoproteins found in vertebrates which bind and consequently mediate the transport of iron (Fe) through blood plasma. They are produced in the liver and contain binding sites for two Iron(III), Fe3+ ions. Human transferrin is ...
. The tetramers of a surface exposed protein, glyceraldehyde-3-phosphate dehydrogenase, are believed to bind to transferrin and remove its iron. Subsequent steps include iron being transferred to surface lipoproteins, then to transport proteins which carry the iron into the cell.
Biochemical characteristics
Colony, morphological, physiological, and biochemical characteristics of marine ''S. epidermidis'' are shown in the table below.
Note: + = Positive, – = Negative, W = Weakly Positive
Identification
The normal practice of detecting ''S. epidermidis'' is by using appearance of colonies on selective media, bacterial morphology by light microscopy, catalase and slide coagulase testing. Zobell agar is useful for the isolation of ''Staphylococcus epidermidis'' from marine organisms.
On the
Baird-Parker agar with
egg yolk
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...
supplement, colonies appear small and black. Increasingly, techniques such as
quantitative PCR
A real-time polymerase chain reaction (real-time PCR, or qPCR when used quantitatively) is a laboratory technique of molecular biology based on the polymerase chain reaction (PCR). It monitors the amplification of a targeted DNA molecule duri ...
are being employed for the rapid detection and identification of ''Staphylococcus'' strains.
Normally, sensitivity to
desferrioxamine can also be used to distinguish it from most other staphylococci, except in the case of ''
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 generally harmless commensal on human and animal skin and ...
'', which is also sensitive. In this case, the production of acid from
trehalose
Trehalose (from Turkish '' tıgala'' – a sugar derived from insect cocoons + -ose) is a sugar consisting of two molecules of glucose. It is also known as mycose or tremalose. Some bacteria, fungi, plants and invertebrate animals synthesize it ...
by ''S. hominis'' can be used to tell the two species apart.
Microbial ecology
Role in foot odor
A common misconception about
foot odor and body odor in general is that sweat itself smells and causes people to smell. However, sweat itself is almost entirely odorless. Rather,
microbes
A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...
present on the skin metabolize certain compounds in sweat as a source of nutrients, producing compounds with an unpleasant smell in the process. S. epidermidis thrives in warm, moist environments and is a common bacteria of the
human microbiome
The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding List of human anatomical features, anatomical sites in which they reside, including the human gastrointes ...
;
it is thus primarily responsible for foot odor as feet have more sweat glands than any other part of the body and thus are often moist, which creates an ideal environment for S. epidermidis to thrive. The bacteria produces
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
s that degrade the leucine present in sweat, producing unpleasant smelling volatile compounds such as isovaleric acid. Feet with stronger odors have a higher density of microorganisms than those with weaker foot odor.
Role in disease
Virulence factors
Biofilm formation
''S. epidermidis'' causes biofilms to grow on plastic devices placed within the body.
This occurs most commonly on intravenous
catheter
In medicine, a catheter ( ) is a thin tubing (material), tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. ...
s and on medical
prostheses. Infection can also occur in dialysis patients or anyone with an implanted plastic device that may have been contaminated. It also causes
endocarditis
Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves. Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, o ...
, most often in patients with defective heart valves. In some other cases,
sepsis
Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs.
This initial stage of sepsis is followed by suppression of the immune system. Common signs and s ...
can occur in hospital patients.
The ability to form
biofilm
A biofilm is a Syntrophy, syntrophic Microbial consortium, community of microorganisms in which cell (biology), cells cell adhesion, stick to each other and often also to a surface. These adherent cells become embedded within a slimy ext ...
s on plastic devices is a major virulence factor for ''S. epidermidis''. One probable cause is surface proteins that bind blood and extracellular matrix proteins. It produces an extracellular material known as polysaccharide intercellular adhesin (PIA), which is made up of sulfated
polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...
s. It allows other bacteria to bind to the already existing biofilm, creating a multilayer biofilm. Such biofilms decrease the metabolic activity of bacteria within them. This decreased metabolism, in combination with impaired diffusion of antibiotics, makes it difficult for antibiotics to effectively clear this type of infection.
Antibiotics are largely ineffective in clearing biofilms. The most common treatment for these infections is to remove or replace the infected implant, though in all cases, prevention is ideal. The drug of choice is often
vancomycin
Vancomycin is a glycopeptide antibiotic medication used to treat certain bacterial infections. It is administered intravenously ( injection into a vein) to treat complicated skin infections, bloodstream infections, endocarditis, bone an ...
, to which
rifampin
Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), ''Mycobacterium avium'' complex, leprosy, and Legionnaires' disease. It is almost always used tog ...
or an
aminoglycoside
Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside (sugar). The term can also refer ...
can be added. Hand washing has been shown to reduce the spread of infection.
Antibiotic resistance
''S. epidermidis'' strains are often
resistant to antibiotics, including
rifamycin
The rifamycins are a group of antibiotics that are synthesized either naturally by the bacterium '' Amycolatopsis rifamycinica'' or artificially. They are a subclass of the larger family of ansamycins. Rifamycins are particularly effective aga ...
,
fluoroquinolones
Quinolone antibiotics constitute a large group of broad-spectrum antibiotic, broad-spectrum bacteriocidals that share a bicyclic molecule, bicyclic core structure related to the substance 4-Quinolone, 4-quinolone. They are used in human and ve ...
,
gentamicin
Gentamicin is an aminoglycoside antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis amo ...
,
tetracycline
Tetracycline, sold under various brand names, is an antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis. It is available in oral an ...
,
clindamycin
Clindamycin is a lincosamide antibiotic medication used for the treatment of a number of bacterial infections, including osteomyelitis (bone) or joint infections, pelvic inflammatory disease, strep throat, pneumonia, acute otitis media (mi ...
, and
sulfonamide
In organic chemistry, the sulfonamide functional group (also spelled sulphonamide) is an organosulfur group with the Chemical structure, structure . It consists of a sulfonyl group () connected to an amine group (). Relatively speaking this gro ...
s.
Methicillin
Methicillin ( USAN), also known as meticillin ( INN), is a narrow-spectrum β-lactam antibiotic of the penicillin class.
Methicillin was discovered in 1960.
Medical uses
Compared to other penicillins that face antimicrobial resistance ...
resistance is particularly widespread, with 75-90% of hospital isolates resistance to methicillin.
Resistant organisms are most commonly found in the intestine, but organisms living on the skin can also become resistant due to routine exposure to antibiotics secreted in sweat.
Acne vulgaris
Preliminary research also indicates ''S. epidermidis'' is universally found inside affected
acne vulgaris
Acne ( ), also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, ...
pores, where ''
Cutibacterium acnes
''Cutibacterium acnes'' (''Propionibacterium acnes'') is the relatively slow-growing, typically aerotolerant anaerobic, gram-positive bacterium (rod) linked to the skin condition of acne; it can also cause chronic blepharitis and endophthalmitis ...
'' is normally the sole resident.
''Staphylococcus epidermidis'' in the normal skin is nonpathogenic and innocuous. But in abnormal lesions (such as openings or cuts on the skin), it becomes pathogenic, likely in
acne vulgaris
Acne ( ), also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, ...
. ''Staphylococcus epidermidis'' enters the sebaceous gland (colonized by ''
Cutibacterium acnes
''Cutibacterium acnes'' (''Propionibacterium acnes'') is the relatively slow-growing, typically aerotolerant anaerobic, gram-positive bacterium (rod) linked to the skin condition of acne; it can also cause chronic blepharitis and endophthalmitis ...
'', the main bacterium that causes acne vulgaris) and damages the hair follicles by producing lipolytic enzymes that change the sebum from fraction to dense (thick) form leading to inflammatory effect.
Moreover, ''S. epidermidis'' biofilm formation by releasing the exopolysaccharide intercellular adhesion (PIA) provides the susceptible anaerobic environment to ''P. acnes'' colonisation and protects it from the innate human immunity molecules.
Both ''P. acnes'' and ''S. epidermidis'' can interact to protect the host skin health from pathogens colonisation. But in the case of competition, they use the same carbon source (i.e. glycerol) to produce short chain fatty acids which act as antibacterial agent against each other. Also, ''S. epidermidis'' helps in skin homeostasis and reduces the ''P. acnes'' pathogenic inflammation by decreasing the
TLR2
Toll-like receptor 2 also known as TLR2 is a protein that in humans is encoded by the ''TLR2'' gene. TLR2 has also been designated as CD282 (cluster of differentiation 282). TLR2 is one of the toll-like receptors and plays a role in the immune sy ...
protein production that induces the skin inflammation.
Role in skin health
Skin barrier reinforcement
Commensal ''S. epidermidis'' also has been shown to contribute to skin barrier homeostasis through the generation of protective ceramides, which helps maintain the integrity of the skin barrier. By modulating the moist, inner lining of some organs and body cavities and their specific immune defense mechanisms, skin commensals interact with infectious agents like pathogens.
Sphingomyelin phosphodiesterase is the main driver in the ''S. epidermidis'' production of
ceramides
Ceramides are a family of waxy lipid molecules. A ceramide is composed of sphingosine and a fatty acid joined by an amide bond. Ceramides are found in high concentrations within the cell membrane of eukaryotic cells, since they are component ...
- a lipid that includes
sphingosine and
sphingosine-1-phosphate. This lipid, both obtains nutrients essential for bacteria and helps the host in the production of ceramides. Ceramides are important components of the
epithelial barrier, and they play a key role in preventing skin from losing moisture; this acts as a protectant and averts against both dehydration and aging of the skin.
Salicylic acid
Salicylic acid is an organic compound with the formula HOC6H4COOH. A colorless (or white), bitter-tasting solid, it is a precursor to and a active metabolite, metabolite of acetylsalicylic acid (aspirin). It is a plant hormone, and has been lis ...
is known to reduce the population of S. epidermidis; the mechanism of this is currently unfamiliar, but it is hypothesized that salicylic acid inhibits S. epidermidis' biofilms.
Metabolic interaction
''S. epidermidis'' plays a key role in metabolic processes that influence skin conditions. The bacterium can affect biochemical pathways within skin cells, which can impact skin health and disease states. Specifically, this is seen in the modulation of the
aryl hydrocarbon receptor
The aryl hydrocarbon receptor (also known as AhR, AHR, ahr, ahR, AH receptor, or as the dioxin receptor) is a protein that in humans is encoded by the AHR gene. The aryl hydrocarbon receptor is a transcription factor that regulates gene express ...
.
In non-atopic skin, ''S. epidermidis'' will help communicate the activation of the aryl hydrocarbon receptor pathway, which both enhances the skin barrier function and helps reduce inflammation. Atopic skin will usually have the inverse effect by acting as a blocker of this pathway and possibly making the skin issue worse.
Immune response
Commensal ''S. epidermidis'' also influences the skin’s immune response. Through interacting with a host’s immune cells, the skin’s mucosal immune defense against various pathogens is strengthened. The skin commensal will directly interfere with harmful pathogens.
In the case of S. aureus, ''S. epidermidis'' may amplify the
innate immune response by causing a reaction of
keratinocytes
Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes refer ...
toward this pathogen.
S. epidermidis produces molecules such as
lipoteichoic acid Lipoteichoic acid (LTA) is a major constituent of the cell wall of gram-positive bacteria. These organisms have an inner (or cytoplasmic) membrane and, external to it, a thick (up to 80 nanometer) peptidoglycan layer. The structure of LTA varies b ...
(LTA), cell wall polysaccharides, peptidoglycan and aldehyde dipeptides which are recognized by
toll-like receptors
Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane protein, single-spanning receptor (biochemistry), receptors usually expressed on sentinel cells such as macrophages ...
(TLRs) as molecules that modulate the immune response. These immunomodulatory molecules create a relationship between bacteria and keratinocytes and have a significant impact in the modulation of the innate immune response, mainly because of their interactions with TLRs.
See also
*
Biofilms
A biofilm is a syntrophic community of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymer ...
*
Microbiology
Microbiology () is the branches of science, scientific study of microorganisms, those being of unicellular organism, unicellular (single-celled), multicellular organism, multicellular (consisting of complex cells), or non-cellular life, acellula ...
* ''
Staphylococcus
''Staphylococcus'', from Ancient Greek σταφυλή (''staphulḗ''), meaning "bunch of grapes", and (''kókkos''), meaning "kernel" or " Kermes", is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillale ...
''
References
Further reading
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External links
Type strain of ''Staphylococcus epidermidis'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q131915
epidermidis
Gram-positive bacteria
Pathogenic bacteria
Bacteria described in 1908
Human microbiome