P0435 Discrimination of Streptococcus pyogenes, Streptococcus agalactiae and Streptococcus dysgalactiae from blood culture samples using high-resolution mass spectrometry Eveliina Tarkka1, Nathalie Friberg1, Juha Grönroos2, Inka Harju2, Kaisu Rantakokko-Jalava2, Karita Haapasalo*3, Jemiina Salo4, Otso Niiranen4, Marjaana Viirtola4, Herdis Friedrich4, Anssi Rantakari4, Sakari Jokiranta3, Pentti Kuusela1

1 HUSLAB Laboratory, Helsinki, Finland, 2 Clinical Microbiology, Turku University Hospital, Turku, Finland, 3 Department of Bacteriology and Immunology, University of Helsinki, Helsinki, Finland, 4 ThermoFischer Scientific, Vantaa, Finland Background: Beta-hemolytic Streptococci, S. pyogenes (group A, GAS), S. agalactiae (group B, GBS) and S. dysgalactiae (group C/G), are human pathogens that cause various infections ranging from local skin and soft- tissue infections to disseminated and invasive infections. GBS can be clinically distinguished from GGS, GCS and GAS infections as it is the most common cause of neonatal sepsis while GGS, GCS and GAS are linked to diseases such as tonsillitis and erysipelas. The skin is a common primary infection focus in streptococcal bacteremias while infection in the urinary tract (adults) or vagina (newborn) often give rise to GBS septicemia. Detection of the primary focus of infection is crucial for diagnosis. Interestingly, in recent years the incidence of S. dysgalactiae has increased making it even more common bacterial pathogen found in positive blood cultures than S. pyogenes. In all, the mortality of bacteremia caused by beta-hemolytic Streptococci is 15 %. Thus, the rapid and accurate identification of the causative agent in blood stream infections is essential to guide correct treatment. Materials/methods: Blood culture positive patient samples containing S. pyogenes, S. agalactiae and S. dysgalactiae were analyzed using high resolution mass spectrometry. Blood culture samples positive for E.coli and S. aureus and other common sepsis causing bacteria, were used as controls in the study. For mass spectrometric analyses, the samples were washed from excess human material prior bacterial cell lysis and bacterial protein extraction. The samples were subjected to solid-phase extraction (SPE) and analyzed with high resolution mass spectrometry using liquid chromatography coupled with a Thermo Scientific™ Orbitrap™ mass spectrometer. Results: Using the high resolution mass spectrometry method described, proteoforms obtained from each of the analyzed samples were used to cluster and effectively discriminate between the different taxa into species level. The clustering results from the high resolution Orbitrap™ mass spectrometry were in agreement with the reference identification results. Conclusions: This study shows that Streptococcus pyogenes, Streptococcus agalactiae and Streptococcus dysgalactiae can be accurately detected from the blood culture samples using high resolution Thermo Scientific™ Orbitrap™ mass spectrometry

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