Staphylococcus aureus as an infectious agent.

Vol. 56 No. 4/2009, 597–612
on-line at: www.actabp.pl

Review

Staphylococcus aureus as an infectious agent: overview of biochemistry and molecular genetics of its pathogenicity
Konrad Plata1,2, Adriana E. Rosato2 and Grzegorz Węgrzyn1
1Department

of Molecular Biology, University of Gdańsk, Gdańsk, Poland; 2Division of Infectious Diseases, Department of Internal Medicine, VirginiaCommonwealth University, Richmond, USA
Received: 22 November, 2009; revised: 07 December, 2009; accepted: 10 Decemebr, 2009 available on-line: 11 December, 2009

Although it is estimated that 20–30% of the general human population are carriers of Staphylococcus aureus, this bacterium is one of the most important etiological agents responsible for healthcare-associated infections. The appearance ofmethicillin resistant S. aureus (MRSA) strains has created serious therapeutical problems. Detailed understanding of the mechanisms of S. aureus infections seems necessary to develop new effective therapies against this pathogen. In this article, we present an overview of the biochemical and genetic mechanisms of pathogenicity of S. aureus strains. Virulence factors, organization of the genome andregulation of expression of genes involved in virulence, and mechanisms leading to methicilin resistance are presented and briefly discussed.
Keywords: Staphylococcus aureus, virulence, pathogenicity genes, toxins, methicillin resistance

BIochemIstry and molecular genetIcs of StaphylococcuS aureuS

Staphylococcus aureus is a Gram-positive spherical bacterium approximately 1 µm in diameter.Its cells form grape-like clusters, since cell division takes place in more than one plane. It is often found as a commensal associated with skin, skin glands, and mucous membranes, particularly in the nose of healthy individuals (Crossley & Archer, 1997). It has been estimated that approx. 20–30% of the general population are S. aureus carriers (Heyman, 2004). On a rich medium, S. aureus formsmedium size “golden” colonies. On sheep blood agar plates, colonies of S. aureus often cause β-hemolysis (Ryan & Ray, 2004). The golden pigmentation of S. aureus colonies is caused by the presence of carotenoids and has been reported to be a virulence factor protecting the

pathogen against oxidants produced by the immune system (Liu et al., 2005). Staphyloccoci are facultative anaerobes capableof generating energy by aerobic respiration, and by fermentation which yields mainly lactic acid. Staphylococcus sp. is catalase-positive, a feature differentiating them from Streptococcus sp., and they are oxidase-negative and require complex nutrients, e.g., many amino acids and vitamins B, for growth. S. aureus is very tolerant of high concentrations of sodium chloride, up to 1.7 molar. Anotherfeature of the Staphylococcus genus is the cell wall peptidoglycan structure that contains multiple glycine residues in the crossbridge, which causes susceptibility to lysostaphin (Crossley & Archer, 1997). S. aureus produces coagulase which interacts with prothrombin in the blood causing plasma to coagulate by converting fibrinogen into fibrin.

Corresponding

author: Grzegorz Węgrzyn,Department of Molecular Biology, University of Gdańsk, Kładki 24, 80-822 Gdańsk, Poland; tel.: (48) 58 523 6308; fax: (48) 58 523 5501; e-mail: wegrzyn@biotech.univ.gda.pl Abbreviations: AIP, auto-inducing peptide; IS, Insertion sequences; MRSA, methicillin resistant Staphylococcus ureus; MSSA, methicillin sensitive S. aureus; MSCRAMMs, microbial surface components recognizing adhesive matrixmolecules; PBPs, penicillin-binding proteins; PNAG, poly-N-acetylglucosamine; PVL, Panton-Valentine leukocidin; SCVs, small-colony variants; SaPIs, superantigen toxins; SCCmec, staphylococcal cassette chromosome mec; TSST, toxic shock syndrome toxin.

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2009

Blood coagulation is used to distinguish S. aureus from others members of the genus, which are collectively...