ISSN 19907508, Biochemistry (Moscow) Supplement Series B: Biomedical Chemistry, 2013, Vol. 7, No. 1, pp. 70–78. © Pleiades Publishing, Ltd., 2013. Original Russian Text © M.A. Kornienko, E.N. Ilina, A.D. Borovskaya, M.V. Edelstein, M.V. Sukhorukova,M. Kostrzewa, V.M. Govorun, 2013, published in Biomeditsinskaya Khimiya. 70 1 INTRODUCTION Staphylococcus aureus attracts traditional interest of researchers specialized in the field of clinical micro biology. First, due to a wide spectrum of inflammatory reactions induced by this microorganism, and second, due to increasing number of drugresistant forms of Staphylococcus species frequently acting as the etiotro pic agent responsible for formation of hospital infec tions. Pathogenicity of staphylococcal strains is mainly determined by the presence of numerous virulence factors [1]. Traditionally, microbial features favoring microorganism distribution in the natural population are considered as the virulence and pathogenicity fac tors of any bacterial pathogenic agent. In the case of Staphylococcus these include formation of antibacte rial drugresistance, production of numerous exotox ins, adhesivity towards human cells, colonization of the epithelium. The main staphylococcal toxins are hemolysins, PantonValentine leukocidin, numerous enterotoxins belonging to the serological types A ⎯E, G, H, J, K ⎯R, toxic shock syndrome toxin, exfoliative 1 To whom correspondence should be addressed. toxins, A and B, etc. The main staphylococcal toxins are proteins with molecular mass from 22 to 34 kDa [2]. Some adhesion and colonization factors are also proteins; for example, αhemolysin encoded by the hla gene is a protein of 33 kDa [1]. αHemolysin exhibits not only cytolytic activity towards monocytes, lymphocytes, erythrocytes, and platelets, it is also needed for biofilm formation and also for adhesion of bacterial cells on the surface of host cells [1, 3]. Since βlactam antibiotics are the most active against S. aureus [4] formation of resistance to these antibacterial drugs is considered as the main pathoge nicity factor. Resistance of S. aureus to penicillin is associated with production βlactamases encoded by the blaZ gene. βLactamases hydrolyze natural and semisynthetic penicillins except methicillin and isox asolylpenicillins. Methicillin resistance in staphylo coccal strains is associated with the presence of an additions penicillinbinding protein exhibiting lower affinity to βlactam antibiotics [5]. This protein is encoded by the gene mecA and the presence of this gene in the staphylococcal genome determines pheno typic resistance to all βlactam antibiotics [4]. Fre quently, the mec cassettes may include genes responsi Strain Differentiation of Staphylococcus aureus by Means of Direct MALDI TOF Mass Spectrometry Profiling M. A. Kornienko a, 1 , E. N. Ilina a , A. D. Borovskaya a , M. V. Edelstein b , M. V. Sukhorukova b , M. Kostrzewa c , and V. M. Govorun a a Research Institute for PhysicalChemical Medicine, ul. M. Pirogovskaya 1a, Moscow, 119435 Russia tel.: +7 (499) 2464570; email: kornienkomariya@gmail.com b Institute of Antimicrobial Chemotherapy, Moscow, Russia c Bruker Daltonik GmbH, Bremen, Germany Received January 11, 2012 Abstract—Staphylococcus aureus is one of the most interesting microbial species in clinical studies. It is char acterized by a wide extent of strain diversity, first of all, due to variability in virulence and pathogenicity. The aim of this study was to test the method of rapid Staphylococcus strain differentiation by a certain sign based on registration of characteristics features of MALDI mass spectra accumulated during direct protein profiling of the bacterial cell. The model signs registered as strain differences included production of βlactamase and αhemolysin encoded by blaZ and hla genes, respectively. The mathematical analysis of MALDI mass spectra accumulated for 53 S. aureus isolates using the clustering genetic algorithm resulted in generation of two independent classification models, which could differentiate the strains by the considered features. Using statistical contribution of each mass peak to the model, the most significant peaks (masses), which could be considered as the markers of Staphylococcus strain differences, were found. The generated diagnostic models were characterized by the following sensitivity and specificity coefficients: 97.5 and 82.5%, respectively, for strain differentiation by βlactamase production and 90.0 and 88.7% by the presence of αhemolysin. Keywords: Staphylococcus, strain differentiation, MALDI TOF mass spectrometry DOI: 10.1134/S1990750813010095