staphylococcus

For more information on staphylococcus, visit Britannica.com.

A genus of bacteria containing at least 28 species that are collectively referred to as staphylococci. Their usual habitat is animal skin and mucosal surfaces. Although the genus is known for the ability of some species to cause infectious diseases, many species rarely cause infections. Pathogenic staphylococci are usually opportunists and cause illness only in compromised hosts. Staphylococcus aureus, the most pathogenic species, is usually identified by its ability to produce coagulase (proteins that affect fibrinogen of the blood-clotting cascade). Since most other species of staphylococci do not produce coagulase, it is useful to divide staphylococci into coagulase-positive and coagulase-negative species. Coagulase-negative staphylococci are not highly virulent but are an important cause of infections in certain high-risk groups. Although Staphylococcus infections were once readily treatable with antibiotics, some strains have acquired genes making them resistant to multiple antimicrobial agents. See also Bacteria; Drug resistance; Medical bacteriology.

Staphylococcus cells are spherical with a diameter of 0.5–1.5 micrometers. Clumps of staphylococci resemble bunches of grapes when viewed with a microscope, owing to cell division in multiple planes. The staphylococci have a gram-positive cell composition, with a unique peptidoglycan structure that is highly cross-linked with bridges of amino acids.

Most species are facultative anaerobes. Within a single species, there is a high degree of strain variation in nutritional requirements. Staphylococci are quite resistant to desiccation and high-osmotic conditions. These properties facilitate their survival in the environment, growth in food, and communicability.

In addition to genetic information on the chromosome, pathogenic staphylococci often contain accessory elements such as plasmids, bacteriophages, pathogenicity islands (DNA clusters containing genes associated with pathogenesis), and transposons. These elements harbor genes that encode toxins or resistance to antimicrobial agents and may be transferred to other strains. Genes involved in virulence, especially those coding for exotoxins and surface-binding proteins, are coordinately or simultaneously regulated by loci on the chromosome. See also Bacterial genetics; Bacteriophage; Plasmid; Transposons.

Most Staphylococcus aureus infections develop into a pyogenic (pus-forming) lesion caused by acute inflammation. Inflammation helps eliminate the bacteria but also damages tissue at the site of infection. Typical pyogenic lesions are abscesses with purulent centers containing leukocytes, fluid, and bacteria. Pyogenic infections can occur anywhere in the body. Blood infections (septicemia) can disseminate the organism throughout the body and abscesses can form internally.

Certain strains of S. aureus produce exotoxins that mediate two illnesses, toxic shock syndrome and staphylococcal scalded skin syndrome. In both diseases, exotoxins are produced during an infection, diffuse from the site of infection, and are carried by the blood (toxemia) to other sites of the body, causing symptoms to develop at sites distant from the infection. Toxic shock syndrome is an acute life-threatening illness mediated by staphylococcal superantigen exotoxins. Staphylococcal scalded skin syndrome, also known as Ritter's disease, refers to several staphylococcal toxigenic infections. It is characterized by dermatologic abnormalities caused by two related exotoxins, the type A and B exfoliative (epidermolytic) toxins. See also Cellular immunology; Toxic shock syndrome.

Staphylococcal food poisoning is not an infection, but an intoxication that results from ingestion of staphylococcal enterotoxins in food. The enterotoxins are produced when food contaminated with S. aureus is improperly stored under conditions that allow the bacteria to grow. Although contamination can originate from animals or the environment, food preparers with poor hygiene are the usual source. Effective methods for preventing staphylococcal food poisoning are aimed at eliminating contamination through common hygiene practices, such as wearing gloves, and proper food storage to minimize toxin production. See also Food poisoning.

Coagulase-positive staphylococci are the most important Staphylococcus pathogens for animals. Certain diseases of pets and farm animals are very prominent. Staphylococcus aureus is the leading cause of infectious mastitis in dairy animals.

A category of bacteria that can cause boils, blood poisoning, and other serious infections.

Pl. staphylococci [Gr.] any organism of the genus Staphylococcus.

• coagulase-positive s. — see coagulase test.

Staphylococcus
SEM micrograph of S. aureus colonies; note the grape-like clustering common to Staphylococcus species.
Scientific classification
Kingdom:	Bacteria
Phylum:	Firmicutes
Class:	Bacilli
Order:	Bacillales
Family:	Staphylococcaceae
Genus:	Staphylococcus Rosenbach 1884
Species
S. afermentans S. aureus S. auricularis S. capitis S. caprae S. cohnii S. epidermidis S. felis S. haemolyticus S. hominis S. intermedius S. lugdunensis S. pettenkoferi S. saprophyticus S. schleiferi S. simulans S. vitulus S. warneri S. xylosus

Not to be confused with streptococcus.

Staphylococcus (from the Greek: σταφυλή, staphylē, "bunch of grapes" and κόκκος, kókkos, "granule") is a genus of Gram-positive bacteria. Under the microscope they appear round (cocci), and form in grape-like clusters.^[1]

The Staphylococcus genus include just thirty-three species.^[2] Most are harmless and reside normally on the skin and mucous membranes of humans and other organisms. Found worldwide, they are a small component of soil microbial flora.^[3]

Contents 1 Role in disease 2 Classification 2.1 Coagulase-positive 2.2 Coagulase-negative 3 Biochemical identification 4 Genomics and molecular biology 5 See also

Role in disease

Main article: Staphylococcal infection

Staphylococcus can cause a wide variety of diseases in humans and other animals through either toxin production or invasion. Staphylococcal toxins are a common cause of food poisoning, as it can grow in improperly-stored food.

Classification

The main classification of staphylococci is based on their ability to produce coagulase, an enzyme that causes blood clot formation.

Coagulase-positive

• S. aureus is coagulase-positive, meaning that they can produce coagulase. However, while the majority of S. aureus are coagulase-positive, some may be atypical in that they do not produce coagulase. S aureus is also catalase-positive (meaning that it can produce the enzyme catalase) and able to convert hydrogen peroxide (H₂O₂) to water and oxygen, which makes the catalase test useful to distinguish Staphylococci from Enterococci and Streptococci.
• S. pseudintermedius inhabits and sometimes infects the skin of domestic dogs and cats is. This organism, too, can carry the genetic material that imparts multiple bacterial resistance. It is rarely implicated in infections in humans, as a zoonosis.

Coagulase-negative

• S. epidermidis, a coagulase-negative staphylococcus species, is a commensal of the skin, but can cause severe infections in immune-suppressed patients and those with central venous catheters.
• S. saprophyticus, another coagulase-negative species that is part of the normal vaginal flora, is predominantly implicated in genitourinary tract infections in sexually-active young women.
• In recent years, several other Staphylococcus species have been implicated in human infections, notably S. lugdunensis, S. schleiferi, and S. caprae.

Common abbreviations for coagulase-negative staphylococcus species are CoNS and CNS.

Biochemical identification

Staphylococcus species can be differentiated from other aerobic and facultative anaerobic gram positive cocci by several simple tests. Staphylococcus spp. are facultative anaerobes. Facultative anaerobes are capable of growth both aerobically and anaerobically. All species grow in the presence of bile salts and are catalase positive. Growth also occurs in a 6.5% NaCl solution. On Baird Parker Medium Staphylococcus spp. show as fermentative, except for S. saprophyticus which is oxidative. Staphylococcus spp. are resistant to Bacitracin (0.04 U resistance = <10mm zone of inhibition) and susceptible to Furazolidone (100μg resistance = <15mm zone of inhibition).

Further biochemical testing is needed to identify down to the species level.

Genomics and molecular biology

The first S. aureus genomes to be sequenced were those of N315 and Mu50 in 2001. Many more complete S. aureus genomes have been submitted to the public databases, making S. aureus one of the most extensively sequenced bacteria. The use of genomic data is now widespread and provides a valuable resource for researchers working with S. aureus. Whole genome technologies such as sequencing projects and microarrays have shown there is an enormous variety of S. aureus strains. Each contains different combinations of surface proteins and different toxins. Relating this information to pathogenic behaviour is one of the major areas of staphylococcal research. The development of molecular typing methods has enabled the tracking of different strains of S. aureus. This may lead to better control of outbreak strains. A greater understanding of how the staphylococci evolve, especially due to the acquisition of mobile genetic elements encoding resistance and virulence genes is helping to identify new outbreak strains and may even prevent their emergence.^[4]

See also

• MRSA
• Staphylococcus aureus
• Staphylus

1. ^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0838585299. 
2. ^ Holt JG (editor) (1994). Bergey's Manual of Determinative Bacteriology (9th ed.). Williams & Wilkins. ISBN 0-683-00603-7. 
3. ^ Madigan M, Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0131443291. 
4. ^ Lindsay J (editor). (2008). Staphylococcus: Molecular Genetics. Caister Academic Press. ISBN 978-1-904455-29-5 . http://www.horizonpress.com/staph. 

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)