Contents lists available at ScienceDirect Comparative Immunology, Microbiology and Infectious Diseases journal homepage: www.elsevier.com/locate/cimid Comparative immunosecretome analysis of prevalent Streptococcus suis serotypes Lidia Gómez-Gascón a,1 , Inmaculada Luque a , Carmen Tarradas a , Alfonso Olaya-Abril b , Rafael J. Astorga a , Belén Huerta a , Manuel J. Rodríguez-Ortega b, ⁎ a Departamento de Sanidad Animal, Universidad de Córdoba, Campus de Excelencia Internacional CeiA3, Córdoba, Spain b Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, Campus de Excelencia Internacional CeiA3, Córdoba, Spain ARTICLE INFO Keywords: Immunoproteomics S. suis Extracellular proteins Secretome ABSTRACT Streptococcus suis is a major Gram-positive swine pathogen associated with a wide variety of diseases in pigs. The efforts made to develop vaccines against this pathogen have failed because of lack of common cross-reactive antigens against different serotypes. Nowadays the interest has moved to surface and secreted proteins, as they have the highest chances to raise an effective immune response because they are in direct contact with host cells and are really exposed and accessible to antibodies. In this work, we have performed a comparative im- munosecretomic approach to identify a set of immunoreactive secreted proteins common to the most prevalent serotypes of S. suis. Among the 67 proteins identified, three (SSU0020, SSU0934, and SSU0215) were those predicted extracellular proteins most widely found within the studied serotypes. These immunoreactive proteins may be interesting targets for future vaccine development as they could provide possible cross-reactivity among different serotypes of this pathogen. 1. Introduction Streptococcus suis is a Gram-positive bacterium responsible for major infections in pigs, which causes different diseases in these animals that include meningitis, arthritis, bronchopneumonia, endocarditis, serositis and septicaemia [1]. Besides the important economic losses in the swine industry, it is also an important zoonotic agent for persons that are in direct contact with diseased pigs or their by-products [2]. Ac- tually, two important outbreaks affecting humans occurred in China in 1998 and 2005, causing several tens of deaths [3,4]. S. suis serotyping is based on the capsular polysaccharide. According to this, 35 serotypes of this pathogen have been described [5]. Ser- otypes 2 (SS2) and 9 (SS9) are considered the most prevalent and virulent types, being frequently isolated from diseased animals [6]. Nevertheless, other serotypes have been associated to different clinical manifestations in pigs. The attempts to control S. suis infections are still hampered by the lack of sufficient knowledge about the pathogenesis of the disease and the lack of sensitive diagnostic methods and effective cross-protective vaccines. Various approaches to obtaining an effective vaccine, especially against the highly prevalent and virulent SS2, have been developed, including the use of bacterins or live-attenuated strains [1]. However, the identification of surfaced-attached proteins (i.e. those having any anchoring or retention motif to the bacterial surface) and secreted factors have received attention during the last years as vaccine candidate agents, because they are expressed in large quantities and are more exposed and thus more accessible to antibodies. Therefore, they have the best chances to raise a high and effective immune response which can be also cross-protective among different serotypes [7]. Ex- tracellularly secreted proteins, which can be surface-associated, also contribute to adapt to and survive in their environment, are important during the course of infection and are in direct contact with host cells and really exposed and accessible to antibodies, therefore having also a good potential for vaccine development [7–9]. The detection of immunoreactive proteins is very helpful to identify potential immunogenic proteins as they are usually the best candidates for the discovery and development of vaccines, as well as for diag- nostics purposes. Proteomics provides excellent means to identify in a fast and reliable way large numbers of proteins. Immunoproteomics, an approach involving two-dimensional electrophoresis followed by im- munoblotting and further MALDI-TOF MS analysis, has been widely used to identify immunogenic proteins and pathogenicity factors in different bacterial species [10–14]. In this study, a comparative https://doi.org/10.1016/j.cimid.2018.06.006 Received 29 October 2017; Received in revised form 13 March 2018; Accepted 10 June 2018 ⁎ Corresponding author at: Departamento de Bioquímica y Biología Molecular, Edificio Severo Ochoa, planta baja, Campus de Rabanales, Universidad de Córdoba, 14071 Córdoba, Spain. 1 Present address: Department of Immunology, University Medicine Greifswald, Sauerbruchstraße DZ7, 17475 Greifswald, Germany. E-mail address: mjrodriguez@uco.es (M.J. Rodríguez-Ortega). Comparative Immunology, Microbiology and Infectious Diseases 57 (2018) 55–61 0147-9571/ © 2018 Elsevier Ltd. All rights reserved. T