Aspects of infective endocarditis. Molecules, microbiology, management, and more

Abstract: AbstractEndocarditis, or heart valve infection, can be caused by a number of pathogens, many of which are Gram-positive bacteria. The diagnosis is based on imaging techniques such as echocardiography and on blood culture. The implementation of fast and accurate species identification methods, such as the matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS) in routine use for bacteria found in blood culture, has meant that bacteria previously thought to be rare have become increasingly recognised in the clinic. Some of these newly recognised bacteria are the aerococci, a genus of bacteria consisting of eight identified species, first identified in 1956. Other areas where MALDI-TOF MS and other new bacteriological methods have been helpful are the differentiation between the groups of NBHS (non-beta-haemolytic streptococci), also known as alpha streptococci, and in the identification of other Gram-positive cocci such as Abiotrophia, Gemella, and Granulicatella.This thesis consists of six different studies on endocarditis and endocarditis-causing Gram-positive bacteria. The first of these covers Aerococcus urinae. Using mass spectrometry, two distinct LPATG-anchored proteins named Asp 1 and Asp 2 were identified on the surface of the bacterium. The presence of these proteins was also confirmed using antibodies generated against recombinantly expressed Asp 1 and Asp 2. After sequencing 25 A. urinae genomes, six different variants of asp genes, named asp1-6, were found. All sequenced isolates contained one or two of these asp-genes located in the same region of the chromosome designated Locus Encoding Aerococcal Surface Protein (LASP).The possible synergy between benzylpenicillin and gentamicin against bacteria has long been an argument used in guidelines recommending combination therapy in infective endocarditis (IE). Two of the studies in this thesis look at this, one of which also describes the characteristics of IE caused by aerococci. Bactericidal synergy was shown against 14 of 24 streptococcal isolates and against 7 of 15 tested aerococcal isolates. The characterisation of aerococcal IE (based on data from the Swedish Endocarditis Registry) showed, amongst other things, that the mean age was significantly higher than in IE caused by NBHS or Staphylococcus aureus.By using a cohort of Swedish patients with NBHS-bacteraemia with or without IE, the HANDOC score was constructed: one point given for heart murmur or heart valve disease (H); one point given for an aetiology of Streptococcus bovis-group, Streptococcus sanguinis-group, or Streptococcus mutans-group, and one point subtracted for Streptococcus anginosus-group bacteraemia (A); one point added if the number of positive blood cultures was two or more (N); one point added for a duration of symptoms of seven days or more (D); one point if only one species was present in the blood culture (O); and one point added for a community-acquired infection (C). Using a cut-off of two points, the sensitivity was 100% for detecting IE and the specificity was 76%. The HANDOC score was then validated in a second cohort of Danish patients with NBHS in blood culture. The HANDOC score and the previously published DENOVA score (originally developed to distinguish IE from non-IE in enterococcal bacteraemia) were then applied in cases of bacteraemia with Aerococcus, Abiotrophia, Gemella, and Granulicatella. The sensitivities of HANDOC and DENOVA were 97% and 93%, respectively, with specificities of 85% and 90%. Thus, HANDOC can possibly be used to decide whether or not to perform IE diagnostics in cases of NBHS bacteremia, and both HANDOC and DENOVA can possibly be used for the decision to perform IE diagnostics in cases of bacteremia with Aerococcus, Abiotrophia, Gemella, or Granulicatella.