staphylococcus

staphylococcus, any of the pathogenic bacteria, parasitic to humans, that belong to the genus Staphylococcus. The spherical bacterial cells (cocci) typically occur in irregular clusters [Gr. staphyle=bunch of grapes]. The term staphylococcus is also sometimes used loosely for the cluster arrangement itself and, broadly, for any bacteria with such a growth pattern. The pigments produced by staphylococci are the basis of the names given to the various strains—those with colors ranging from orange to yellow are designated S. aureus; white strains are known as S. albus.

Staphylococci cause abscesses, boils, and other infections of the skin, such as impetigo. They can also produce infection in any organ of the body (e.g., staphylococcal pneumonia of the lungs). The most common form of food poisoning is brought on by staphylococcus-contaminated food. The staphylococcus organisms also generate toxins and enzymes that can destroy both red and white blood cells.

Unlike some other types of bacteria, staphylococci are generally partly or wholly resistant to antibiotic action; this raises serious problems in the treatment and control of staphylococcus infections (see drug resistance). The rise of drug-resistant virulent strains of S. aureus, particularly methicillin-resistant S. aureus (MRSA), has led increasing concern in the medical community. Although sick patients with compromised immune systems and children are most susceptible to the strains, which most typically are contracted in hospital, nursing home, and other health-care settings, healthy persons have also been infected. Pharmaceutical companies are working to develop new antibiotics to kill drug-resistant strains of staphylococcus and other bacteria, and a vaccine for S. aureus has been developed.

Any of the spherical bacteria that make up the genus Staphylococcus. The best-known species are present in great numbers on the mucous membranes and skin of all humans and other warm-blooded animals. The cells characteristically group together in grapelike clusters. Staphylococci are gram-positive (see gram stain) and stationary and do not require oxygen. Of significance to humans is the species S. aureus, an important agent of wound infections, boils, and other human skin infections, and one of the most common causes of food poisoning. It also causes udder inflammation in domestic animals and breast infections in women. The largest cause of hospital infections (accounting for almost 15percnt), “staph” is often difficult to treat because of its increasing resistance to antibiotics.

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Staphylococcus (in Greek σταφυλη staphyle means bunch of grapes and κοκκος coccos means granule) is a genus of Gram-positive bacteria. Under the microscope they appear round (cocci), and form in grape-like clusters.

The Staphylococcus genus include just thirty-one species. 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.

Role in disease

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.

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 where 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.

See also

• Staphylus
• Staphylococcus aureus

References