Editor’s Choice Invasion of endothelial cells and arthritogenic potential of endocarditis-associated Corynebacterium diphtheriae Renata Stavracakis Peixoto, 1,2 3 Gabriela Andrade Pereira, 1,2 3 Louisy Sanches dos Santos, 1 Cla ´ udio Marcos Rocha-de-Souza, 1 De ´ bora Leandro Rama Gomes, 3 Cintia Silva dos Santos, 1,2 Lucia Maria Correa Werneck, 4 Alexandre Alves de Souza de Oliveira Dias, 4 Raphael Hirata Jr, 1 Prescilla Emy Nagao 5 and Ana Luı ´za Mattos-Guaraldi 1 Correspondence Ana Luı ´za Mattos-Guaraldi guaraldi@uerj.br Received 27 May 2013 Accepted 13 December 2013 1 Laboratory of Diphtheria and Corynebacteria of Clinical Relevance (LDCIC), Faculty of Medical Sciences, Rio de Janeiro State University (UERJ), Rio de Janeiro, RJ, Brazil 2 Department of Medical Microbiology, Institute of Microbiology, Rio de Janeiro Federal University (IMPPG/UFRJ), Rio de Janeiro, RJ, Brazil 3 Faculty of Pharmacy, Federal Institute of Education, Science and Technology of Rio de Janeiro (IFRJ), Rio de Janeiro, RJ, Brazil 4 National Institute for Quality Control in Health (INCQS), Fundac ¸a ˜ o Oswaldo Cruz (FIOCRUZ), Rio de Janeiro, RJ, Brazil 5 Biology Institute Roberto Alca ˆ ntara Gomes, Rio de Janeiro State University (UERJ), Rio de Janeiro, RJ, Brazil Although infection by Corynebacterium diphtheriae is a model of extracellular mucosal pathogenesis, different clones have been also associated with invasive infections such as sepsis, endocarditis, septic arthritis and osteomyelitis. The mechanisms that promote C. diphtheriae infection and haematogenic dissemination need further investigation. In this study we evaluated the association and invasion mechanisms with human umbilical vein endothelial cells (HUVECs) and experimental arthritis in mice of endocarditis-associated strains and control non-invasive strains. C. diphtheriae strains were able to adhere to and invade HUVECs at different levels. The endocarditis-associated strains displayed an aggregative adherence pattern and a higher number of internalized viable cells in HUVECs. Transmission electron microscopy (TEM) analysis revealed intracellular bacteria free in the cytoplasm and/or contained in a host-membrane-confined compartment as single micro-organisms. Data showed bacterial internalization dependent on microfilament and microtubule stability and involvement of protein phosphorylation in the HUVEC signalling pathway. A high number of affected joints and high arthritis index in addition to the histopathological features indicated a strain-dependent ability of C. diphtheriae to cause severe polyarthritis. A correlation between the arthritis index and increased systemic levels of IL-6 and TNF-a was observed for endocarditis-associated strains. In conclusion, higher incidence of potential mechanisms by which C. diphtheriae may access the bloodstream through the endothelial barrier and stimulate the production of pro-inflammatory cytokines such as IL-6 and TNF-a, in addition to the ability to affect the joints and induce arthritis through haematogenic spread are thought to be related to the pathogenesis of endocarditis-associated strains. INTRODUCTION Corynebacterium diphtheriae is the causative agent of diph- theria, a toxemic localized infection of the respiratory tract. Furthermore, C. diphtheriae is not only the aetiological agent of diphtheria, but can cause other infections as well (Ott et al., 2010). Systemic infections caused by 3These authors contributed equally to this paper. Abbreviations: FAS, FITC-labelled phalloidin assay; HUVEC, human umbilical vein endothelial cell; i.v., intravenously; SW, Swiss Webster; TEM, transmission electron microscopy. Microbiology (2014), 160, 537–546 DOI 10.1099/mic.0.069948-0 069948 G 2014 SGM Printed in Great Britain 537