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

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

Infection or Contamination with Rothia, Kocuria, Arthrobacter and Pseudoglutamicibacter — a Retrospective Observational Study of Non-Micrococcus Micrococcaceae in the Clinic

Rothia, Kocuria, Arthrobacter, and Pseudoglutamicibacter are bacterial species within the family Micrococcaeae. Knowledge of human infections due to these bacteria is limited. This study aimed to examine features of infections caused by non-Micrococcus Micrococcaeae (NMM). Findings of NMM from blood cultures and other sterile cultures from 2012 to 2021 were identified from the records of the Department of Clinical Microbiology in Region Skåne, Lund, Sweden. Medical records were retrospectively reviewed. True infection was defined as having signs of infection, no other more likely pathogen, and no other focal infection, together with two positive blood cultures or one positive blood culture and an intravascular device. A total of 197 patients with findings of NMM in blood cultures were included. Among adult patients with bacteremia, 29 patients (22%) were considered to have a true infection. Adults with true infection were significantly more likely to have malignancy (69%), leukopenia (62%), and treatment with chemotherapeutics (66%) compared to patients with contaminated samples (24%, 3%, and 8%, respectively) (

Clinical Significance of a 16S-rDNA Analysis of Heart Valves in Patients with Infective Endocarditis : a Retrospective Study

A substantial proportion of patients with infective endocarditis (IE) are subjected to heart valve surgery. Microbiological findings on valves are important both for diagnostics and for tailored antibiotic therapy, post-operatively. The aims of this study were to describe microbiological findings on surgically removed valves and to examine the diagnostic benefits of 16S-rDNA PCR and sequencing (16S-analysis). Adult patients who were subjected to heart valve surgery for IE between 2012 and 2021 at Skåne University Hospital, Lund, where a 16S-analysis had been performed on the valve, constituted the study population. Data were gathered from medical records, and the results from blood cultures, valve cultures, and 16S-analyses of valves were compared. A diagnostic benefit was defined as providing an agent in blood culture negative endocarditis, providing a new agent in episodes with positive blood cultures, or confirming one of the findings in episodes with a discrepancy between blood and valve cultures. 279 episodes in 272 patients were included in the final analysis. Blood cultures were positive in 259 episodes (94%), valve cultures in 60 episodes (22%), and 16S-analyses in 227 episodes (81%). Concordance between the blood cultures and the 16S-analysis was found in 214 episodes (77%). The 16S-analyses provided a diagnostic benefit in 25 (9.0%) of the episodes. In blood culture negative endocarditis, the 16S-analyses had a diagnostic benefit in 15 (75%) of the episodes. A 16S-analysis should be routinely performed on surgically removed valves in blood culture negative endocarditis. In patients with positive blood cultures, 16S-analysis may also be considered, as a diagnostic benefit was provided in some patients.IMPORTANCE This work demonstrates that it can be of importance to perform both cultures and analysis using 16S-rDNA PCR and sequencing of valves excised from patients undergoing surgery for infective endocarditis. 16S-analysis may help both to establish a microbiological etiology in cases of blood culture negative endocarditis and to provide help in situations where there are discrepancies between valve and blood cultures. In addition, our results show a high degree of concordance between blood cultures and 16S-analyses, indicating that the latter has a high sensitivity and specificity for the etiological diagnosis of endocarditis in patients who were subjected to heart valve surgery

True infection or contamination in patients with positive Cutibacterium blood cultures-a retrospective cohort study

Cutibacterium is a genus often considered a contaminant when present in blood cultures, but it can also cause severe infections, especially related to implanted foreign materials. We investigated the incidence and features of patients with true Cutibacterium infection. Patients with positive Cutibacterium blood cultures between the years 2015-2020 in southern Sweden were identified through microbiology records and medical records were studied retrospectively. Cutibacterium isolates were species determined using MALDI-TOF MS. Patients were classified as having true infection or contamination according to a definition considering both clinical and microbiological features and these groups were compared. A total of 313 episodes of positive Cutibacterium blood cultures were identified in 312 patients. Of these, 49 (16%, corresponding to an incidence of 6 cases per million inhabitants per year) were classified as true infections. The most common species was Cutibacterium acnes (87%), and the majority were elderly men with comorbidities. Patients with true Cutibacterium infection often had an unknown focus of infection (n = 21) or a focus in the respiratory tract (n = 18). We identified one episode of ventriculo-peritoneal shunt infection, three episodes of aortic stent-graft infection, and one episode of infective endocarditis. Two patients, where Cutibacterium was isolated at the site of infection, had only one positive blood culture. The finding of positive Cutibacterium blood cultures should not always be considered contamination. Definitions of true Cutibacterium bacteremia with a demand that more than one blood culture must be positive may miss true infections

Blood culture time to positivity in non-β-hemolytic streptococcal bacteremia as a predictor of infective endocarditis-a retrospective cohort study

Non-β-hemolytic streptococci (NBHS) cause infective endocarditis (IE) and a short blood culture time to positivity (TTP) is associated with risk of IE in bacteremia with other pathogens. In this retrospective population-based cohort study, we investigate if TTP is associated to IE or mortality. Of 263 episodes with NBHS bacteremia, 28 represented IE and the median TTP did not differ significantly between episodes with IE (15 h) and non-IE (15 h) (p=0.51). TTP was similar among those who survived and those who died within 30 days. However, TTP significantly differed when comparing the different streptococcal groups (p<0.001)

Incidence, aetiology and temporal trend of bloodstream infections in southern Sweden from 2006 to 2019 : a population-based study

BackgroundBloodstream infections (BSI) are a public health concern, and infections caused by resistant bacteria further increase the overall BSI burden on healthcare.AimTo provide a population-based estimate of BSI incidence and relate this to the forthcoming demographic ageing western population change.MethodsWe retrieved positive blood cultures taken from patients in the Skåne region, southern Sweden, 2006-2019 from the Clinical Microbiology Department database and estimated incidence rates (IR), stratified by age (0-49, 50-64, 65-79, ≥ 80 years), sex, year, and species and described antimicrobial susceptibility for Enterobacterales.ResultsWe identified 944,375 blood culture sets, and 129,274 (13.7%) were positive. After deduplication and removal of contaminants, 54,498 separate BSI episodes remained. In total, 30,003 BSI episodes (55%) occurred in men. The overall IR of BSI was 307/100,000 person-years, with an average annual increase of 3.0%. Persons ≥ 80 years had the highest IR, 1781/100,000 person-years, as well as the largest increase. Escherichia coli (27%) and Staphylococcus aureus (13%) were the most frequent findings. The proportion of Enterobacterales isolates resistant to fluoroquinolones and third generation cephalosporins increased from 8.4% to 13.6%, and 4.9% to 7.3%, (p for trend < 0.001), with the largest increase in the oldest age group.ConclusionWe report among the highest BSI IRs to date worldwide, with a higher proportion among elderly persons and males, including resistant isolates. Given expected demographic changes, these results indicate a possible substantial future BSI burden, for which preventive measures are needed

A Population-Based Study of Unfavorable Prognostic Factors Associated With Pyogenic Liver Abscess

BackgroundPyogenic liver abscess (PLA) is a rare entity that is associated with substantial mortality and morbidity. Our objective was to investigate variables associated with mortality and subsequent PLA in patients diagnosed with PLA in southern Sweden.MethodsWe conducted a population-based observational study comprising all episodes of PLA that occurred between 2011 and 2020 in the county of Skåne, southern Sweden. The primary outcome was defined as all-cause 90-day mortality and the secondary outcome was defined as the occurrence of a subsequent PLA.ResultsA total of 452 episodes of PLA occurred in 360 patients during the study period. The 90-day mortality rate was 16% (n = 58) and the subsequent PLA rate was 20% (n = 92). In a multivariable logistic regression model, female sex (odds ratio [OR], 2.0 [95% confidence interval {CI}, 1.1–3.9]), malignancy (OR, 3.7 [95% CI, 1.9–7.1]), liver failure (OR, 6.3 [95% CI, 2.7–14.5]), and polymicrobial findings (OR, 3.8 [95% CI, 2.2–6.9]) were associated with death within 90 days (P < .05). Male sex (OR, 2.1 [95% CI, 1.2–3.6]), malignancy (OR, 2.1 [95% CI, 1.3–3.6]), age (64–74 years: OR, 2.5 [95% CI, 1.3–4.8]), and chronic liver disease (OR, 3.0 [95% CI, 1.4–6.5]) were associated with the risk of subsequent PLA (P ≤ .01).ConclusionsIdentifying different clinical variables associated with an unfavorable outcome may improve the management and treatment of patients with PLA and thus prevent the risk of death and subsequent PLA

Rapid diagnostic testing for SARS-CoV-2 : Validation and comparison of three point-of-care antibody tests

With the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a need for diagnostic tests has surfaced. Point-of-care (POC) antibody tests can detect immunoglobulin (Ig) G and M against SARS-CoV-2 in serum, plasma, or whole blood and give results within 15 min. Validation of the performance of such tests is needed if they are to be used in clinical practice. In this study, we evaluated three POC antibody tests. Convalescent serum samples from 47 reverse transcription-polymerase chain reaction (RT-PCR) verified patients with coronavirus disease 2019 (COVID-19) collected at least 28 days post RT-PCR diagnosis as well as 50 negative pre-COVID-19 controls were tested. The three tests (denoted the J-, N-, and Z-tests) displayed the sensitivities of 87%, 96%, and 85%, respectively, for the detection of IgG. All tests had the same specificity for IgG (98%). The tests did not differ significantly for the detection of IgG. The sensitivities for IgM were lower (15%, 67%, and 70%) and the specificities were 90%, 98%, and 90%, respectively. The positive and negative predictive values were similar among the tests. Our results indicate that these POC antibody tests might be accurate enough to use in routine clinical practice

Identification of two abundant Aerococcus urinae cell wall-anchored proteins

Aerococcus urinae is an emerging pathogen that causes urinary tract infections, bacteremia and infective endocarditis. The mechanisms through which A. urinae cause infection are largely unknown. The aims of this study were to describe the surface proteome of A. urinae and to analyse A. urinae genomes in search for genes encoding surface proteins. Two proteins, denoted Aerococcal surface protein (Asp) 1 and 2, were through the use of mass spectrometry based proteomics found to quantitatively dominate the aerococcal surface. The presence of these proteins on the surface was also shown using ELISA with serum from rabbits immunized with the recombinant Asp. These proteins had a signal sequence in the amino-terminal end and a cell wall-sorting region in the carboxy-terminal end, which contained an LPATG-motif, a hydrophobic domain and a positively charged tail. Twenty-three additional A. urinae genomes were sequenced using Illumina HiSeq technology. Six different variants of asp genes were found (denoted asp1-6). All isolates had either one or two of these asp-genes located in a conserved locus, designated Locus encoding Aerococcal Surface Proteins (LASP). The 25 genomes had in median 13 genes encoding LPXTG-proteins (range 6-24). For other Gram-positive bacteria, cell wall-anchored surface proteins with an LPXTG-motif play a key role for virulence. Thus, it will be of great interest to explore the function of the Asp proteins of A. urinae to establish a better understanding of the molecular mechanisms by which A. urinae cause disease