Higher order taxa:
Bacteria; Firmicutes; Bacilli; Bacillales; Staphylococcaceae; Staphylococcus
Staphylococcus aurous, S. epidermidis
Description and Significance
As a pathogen, it is important to understand the virulence mechanisms of Staphylococcus in order to successfully combat the pathogen. Strains of Staphylococcus resistant to our most powerful antibiotics have increased pressure on researchers to find alternative, more effective ways of fighting Staphylococcus.
There are currently 11 genome projects, 9 of which are complete and 2 are in process. The Staphylococcus aureus genome, which is the most common species amoung the genome projects, is about 2.8 Mega-base pairs long with approximately 2,600 open reading frames, comprising 84.5% of the genome. It has a G+C content of about 33%, and a single plasmid about 25,000 base pairs in length with a G+C content of 28.7%. The genes for antibiotic resistance in Staphylococcus aureus are located on plasmids or other similar structures. Staphylococcus epidermidis, which has two genomes sequenced in the speices, is about 2.5 Mega-base pairs long with 1,681 open reading frames and its G+C content is 32%. Staphylcoccus haemolyticus is about 2.68 Mega-base pairs long with a G+C content of 32%.
Cell Structure and Metabolism
Staphylococci are spherical Gram-positive bacteria, which are immobile and form grape-like clusters. They form bunches because they divide in two planes as opposed to their close relatives streptococci which, although they are similarly shaped, form chains because they divide only in one plane. Staphylococci are facultative anaerobes. They mainly grow by aerobic respiration, or fermentation that produces lactic acid.
There are two different types of colonies formed. Those formed by S. aureus are yellow and become rather large on a rich medium, while those of S. epidermidi are white and form relatively small colonies, even on a rich medium.
Staphylococcus aureus is a normal inhabitant of the skin and mucous membranes in the nose of a healthy human, while S. epidermidis inhabits only the skin of healthy humans.
Staphylococcus usually only infects immunocompromised humans, and is an extremely versatile pathogen. Infections usually remain localized at the point of entry by host defenses. S. aureus is one of the major causes of hospital-aquired infection. Foreign bodies, such as sutures, indwelling catheters, and implanted joints, are extremely susceptible to Staphylococcus epidermidis colonization, and often serve as the point of entry for infection. Another common path of infection is the respiratory tract, where the bacterium causes pneumonia. By forming biofilms Staphylococcus epidermidis is resistant to antibiotics, antibodies, and phagocytosis, and can serve as a reservoir for antibiotic resistant genes that can be transferred to other bacteria. Other diseases caused by staphylococci include boils, sinusitis, emesis, diarrhea, endocarditis, scalded skin syndrome, osteomyelitis, urinary tract infection, and toxic shock syndrome. During the 1970s a strain of Staphylococcus aureus resistant to the antibiotic meticillin, was isolated and consequently vancomycin (the most powerful antibiotic in our arsenal) became the primary antibiotic used to combat staphylococcus infection. In 1997 a strain of S. aureus resistant to vancomycin was isolated, and people are once again exposed to the threat of untreatable staphylococcus infection. The sequencing of the S. aureus genome will hopefully provide insight into how the organism generates such a variety of toxins, and aid researchers in developing ways of combating the versatile bacterium.
Gill S.R., Founts D. E., ARcher G. L., Mongodis E. F., Deboy R. T., Ravel J., Paulsen I. T., Kolonay J. F., Brinkac L., Beanan M., Dodson R. J., Daughtery S. C., Madupu R., Angiuoli S. V., Durkin A. S., Haft D. H., Vamathevan J., Khouri H., Utterback T., Lee C., Dimitrov G., Jiang L., Qin H., Weidman J., Tran K., Kang K., Hance I. R., Nelson K. E., Fraser C. M. "Insights on evolution of virulence and resistance from the complete genome analysis of an early methicillin-resistant Staphylococcus aureus strain and a biofilm-producing methicillin-resistant Staphylococcus epidermidis strain." Journal of bacteriology 2005 Apr;187(7):2426-38.