Typing of Staphylococcus aureus in order to determine the spread of drug resistant strains inside and outside hospital environment.

Staphylococcus aureus is one of the most important etiological factors of both nosocomial and community-acquired infections. Multidrug-resistant S. aureus is frequently isolated nowadays. Antibiotics used on the hospital ward exert a selective pressure on the strains and favor resistant strains. Multidrug-resistant and highly virulent strains can spread not only within the hospital but also between hospitals. Numerous studies show a predominance of one clone on a specific territory. The spread of such dangerous clones to neighboring countries and the entire continent is possible. Typing methods are very useful in infection control and prevention. Modern methods which are based on sequencing are necessary in rationalizing of infection control programs. Typing of Staphylococcus aureus includes methods that allow to determine the spread of drug-resistant pathogens. 'Gold standard' is pulsed-field gel electrophoresis (PFGE), which relies on separating the DNA fragments after restriction cutting. MLST (Multi Locus Sequence Typing) is based on a comparison of"housekeeping" gene sequences controlling the basic cell functions. With the MLST method, it is possible to demonstrate a broad, international spread of the specific clones. However, for epidemiological investigations, MLST seems to be too time-consuming and expensive to be used as a basic typing tool. The complementary method is spa typing, based on the sequencing of short repetitive sequences of the polymorphic X region from the gene encoding protein A. This method can be used for studying molecular evolution of S. aureus, as well as for testing for hospital outbreaks. It is faster and cheaper than MLST. It is also necessary to subtype the elements responsible for methycillin resistance (SCCmec), which allows to distinguish MRSA (Methicillin-resistant Staphylococcus aureus) clones with a common ancestor, but different epidemiological origin. All of those methods have their specific advantages and disadvantages and there is no single method efficient and suitable in any case.