Staphylococcus

The nomenclature used here follows the List of Prokaryotic names with Standing in Nomenclature (LPSN). The type species is Staphylococcus aureus, and LPSN recognizes 76 species with correct names in the genus.^[1]

In 2020, five species were transferred to the newly established genus Mammaliicoccus: M. fleurettii, M. lentus, M. sciuri, M. stepanovicii, and M. vitulinus.^[5] LPSN currently treats Mammaliicoccus as a heterotypic synonym of Staphylococcus and therefore retains the corresponding Staphylococcus names, whereas the NCBI taxonomy database and GTDB continue to recognize Mammaliicoccus as a separate genus.^[1][6][7]

The following phylogenomic tree is a pruned version of the bacterial reference tree from GTDB release R11-RS232, inferred from 120 marker proteins.^[8][9][7] It includes named GTDB species clusters whose names are treated as correct by LPSN.^[1] Unnamed clusters, letter-suffixed GTDB clusters, and species lacking a corresponding named cluster are not shown.

Staphylococcus cells have a thick peptidoglycan cell wall containing teichoic acids. Most members are catalase-positive and facultatively anaerobic, although physiological characteristics vary among species. Many species also tolerate elevated salt concentrations.^[2]

In the laboratory, catalase activity is commonly used to distinguish staphylococci from streptococci and enterococci. Coagulase and other biochemical reactions can then assist with species identification. Closely related species may require molecular methods or MALDI-TOF mass spectrometry for reliable identification.^[10]

Coagulase activity, the ability to cause plasma clotting, is an important phenotypic characteristic used to distinguish groups of staphylococci. Nine species have conventionally been described as coagulase-positive: S. argenteus, S. aureus, S. coagulans, S. cornubiensis, S. delphini, S. intermedius, S. lutrae, S. pseudintermedius, and S. schweitzeri. S. agnetis, S. chromogenes, and S. hyicus have been described as coagulase-variable.^[11]

A genus-wide study found that 13 species coagulated at least one of six tested animal plasmas, including S. condimenti, which had previously been considered coagulase-negative. The observed phenotype varied with the bacterial species, strain, and source of the plasma. Across the genus, activity was associated principally with von Willebrand factor-binding protein, whereas the classical staphylocoagulase gene was restricted to the S. aureus complex.^[11]

Species that do not routinely produce coagulase are collectively called coagulase-negative staphylococci (CoNS). This is a phenotypic grouping rather than a formal taxonomic group and includes both commensal and opportunistically pathogenic species.^[10]

Complete genome sequences for the methicillin-resistant S. aureus strains N315 and Mu50 revealed chromosomes containing numerous genes associated with virulence and antimicrobial resistance, including genes carried by mobile genetic elements.^[12]

Comparative genomic studies have documented extensive variation in accessory genes among staphylococcal strains. Horizontal gene transfer contributes to the distribution of antimicrobial-resistance and virulence genes and also affects genes outside recognized mobile elements.^[13]

Members of Staphylococcus commonly colonize the skin and mucosal surfaces of mammals and birds. Host associations range from relatively broad to more restricted, and some animal-associated species are also opportunistic pathogens.^[14][11]

Staphylococci also occur in foods and environmental habitats.^[2] Members of the genus have, for example, been detected in floral nectar microbial communities.^[15]

Staphylococcus aureus can be carried asymptomatically on the skin or in the nose but can also cause skin and soft-tissue infections, bloodstream infections, pneumonia, endocarditis, osteomyelitis, and infections associated with implanted medical devices.^[4][16] Methicillin-resistant strains are collectively known as MRSA. In healthcare settings, the risk of serious infection is increased among patients in intensive care, patients with weakened immune systems, those undergoing certain operations, and those with indwelling medical devices.^[4]

Coagulase-negative species are often components of the normal microbiota but can cause opportunistic infections. S. epidermidis is associated particularly with infections of catheters and other implanted devices, S. saprophyticus is a cause of urinary tract infection, and S. lugdunensis can cause invasive disease.^[10]

In bloodstream infection, S. aureus virulence factors contribute to tissue adhesion, immune evasion, host-cell injury, inflammation, altered coagulation, and loss of vascular integrity, which can culminate in sepsis and septic shock.^[17]

• Methicillin-resistant S. aureus (MRSA)
• Vancomycin-resistant S. aureus (VRSA)