Severity and properties of cardiac damage caused by Streptococcus pneumoniae are strain dependent

RESEARCH ARTICLE Severity and properties of cardiac damage caused by Streptococcus pneumoniae are strain dependent Anukul T. Shenoy1☯¤, Sarah M. Beno1☯, Terry Brissac ID1, Jeremiah W. Bell1, Lea Novak2, Carlos J. Orihuela ID1* a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 1 Department of Microbiology, The University of Alabama at Birmingham, Birmingham, Alabama, United States of America, 2 Department of Pathology, The University of Alabama at Birmingham, Birmingham, Alabama, United States of America ☯ These authors contributed equally to this work. ¤ Current address: Pulmonary Center–Boston University School of Medicine, Boston, Massachusetts, United States of America * Abstract OPEN ACCESS Citation: Shenoy AT, Beno SM, Brissac T, Bell JW, Novak L, Orihuela CJ (2018) Severity and properties of cardiac damage caused by Streptococcus pneumoniae are strain dependent. PLoS ONE 13(9): e0204032. https://doi.org/ 10.1371/journal.pone.0204032 Editor: D. Ashley Robinson, University of Mississippi Medical Center, UNITED STATES Received: March 15, 2018 Accepted: August 31, 2018 Published: September 14, 2018 Copyright: © 2018 Shenoy et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by National Institutes of Health (http://grants.nih.gov/) grant AI114800 and American Heart Association (http:// research.americanheart.org) award 16GRNT30230007 awarded to CJO. SMB was supported by National Institutes of Health (http:// grants.nih.gov/) grant 1 K12 GM 088010-09. The funders had no role in study design, data collection Streptococcus pneumoniae is an opportunistic Gram-positive pathogen that can cause invasive disease. Recent studies have shown that S. pneumoniae is able to invade the myocardium and kill cardiomyocytes, with one-in-five adults hospitalized for pneumococcal pneumonia having a pneumonia-associated adverse cardiac event. Furthermore, clinical reports have shown up to a 10-year increased risk of adverse cardiac events in patients formerly hospitalized for pneumococcal bacteremia. In this study, we investigated the ability of nine S. pneumoniae clinical isolates, representing eight unique serotypes, to cause cardiac damage in a mouse model of invasive disease. Following intraperitoneal challenge of C57BL/6 mice, four of these strains (D39, WU2, TIGR4, and 6A-10) caused high-grade bacteremia, while CDC7F:2617–97 and AMQ16 caused mid- and low-grade bacteremia, respectively. Three strains did not cause any discernible disease. Of note, only the strains capable of high-grade bacteremia caused cardiac damage, as inferred by serum levels of cardiac troponin-I. This link between bacteremia and heart damage was further corroborated by Hematoxylin & Eosin and Trichrome staining which showed cardiac cytotoxicity only in D39, WU2, TIGR4, and 6A-10 infected mice. Finally, hearts infected with these strains showed varying histopathological characteristics, such as differential lesion formation and myocytolysis, suggesting that the mechanism of heart damage varied between strains. Introduction Streptococcus pneumoniae (the pneumococcus) is a Gram-positive bacteria and common resident of the human nasopharynx. It is also an opportunistic pathogen that can cause many different types of disease including otitis media, pneumonia, bacteremia, and meningitis [1]. PLOS ONE | https://doi.org/10.1371/journal.pone.0204032 September 14, 2018 1 / 15 Properties of cardiac damage caused by Streptococcus pneumoniae differ by strain and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. These infections primarily occur in the very young and old, as their immune systems are under-developed or waning, respectively [2–4]. While the overall attack rate of the pneumococcus is low, so many individuals are colonized that the pneumococcus is among the leading causes of infectious deaths worldwide [5, 6]. The World Health Organization estimates that 500,000 children under five years of age die each year from pneumococcal disease [7]. Furthermore, the overall mortality associated with invasive pneumococcal disease (IPD) in adults increases from 1.53/100,000 at 50 years of age to 11.56/100,000 at 85+ [8]. A link between pneumonia and acute cardiac events has been known since the 1930s [9–11]. Several recent clinical studies by Corrales-Medina have revived an appreciation for this serious complication of pneumonia [12, 13]. Relevant to our study, Musher et al. showed that up to 20% of adults hospitalized for pneumococcal pneumonia experienced congestive heart failure, arrhythmia, and myocardial infarction, either alone or in combination [14]. These individuals were up to fourfold more likely to die than those hospitalized for pneumococcal pneumonia without a cardiac complication [14]. Even more recently, Eurich et al. showed that pneumococcal bacteremia is a risk-factor for adverse cardiac events in convalescence for up to 10 years [15]. Thus, some form of acute and long-lasting cardiac damage is incurred during severe pneumonia that results in invasive pneumococcal disease (IPD). Helping to explain why this occurs, our laboratory has recently demonstrated that S. pneumoniae is capable of translocation across the vascular endothelium and invasion of the myocardium from the bloodstream. Within the heart, S. pneumoniae kill cardiomyocytes and resident and infiltrating macrophages, causing extensive myocardial damage [16–19]. At sublethal levels, pneumococcal cell wall and pneumolysin, the S. pneumoniae pore-forming toxin, also impair cardiac contractility [20, 21]. The former is due to cell wall ligation of platelet-activating factor receptor and toll-like receptor 2 which can activate NFkB; NFkB activation is inhibitory to cardiac contractility [22]. The latter the result of pneumolysin-mediated membrane damage which disrupts the calcium signaling that is essential for muscle contraction [21]. Together, these and the physiological stressors that are present during severe infection result in cardiac dysfunction and heart failure. Importantly, the majority of work on S. pneumoniae invasion in vivo using the mouse model has been done using two strains: serotype 4 strain TIGR4 and serotype 2 strain D39. In the heart, TIGR4 actively replicates to form bacteria-filled lesions, which we have called cardiac microlesions. TIGR4 in microlesions have salient biofilm properties, such as intrinsic resistance to antimicrobials [19]. In contrast, strain D39 does not form these lesions; nonetheless, D39 is associated with considerable tissue damage and the infiltration of immune cells a (...truncated)