Streptococcus bovis endocarditis: Update from a multicenter registry

Usefulness of newer testing modalities for the accurate diagnosis of culture-negative endocarditis

A woman in her 80s with a history of congestive heart failure, atrial arrhythmia treated with atrioventricular nodal ablation and permanent pacemaker (PPM) placement, mitral valve disease status post-repair and colon cancer status post-treatment was admitted for further evaluation of severe dyspnea on exertion. Imaging revealed vegetation on both the prosthetic mitral valve and the PPM lead. Blood cultures were collected without growth, so a cell-free DNA Karius test was performed, which can detect over 1000 pathogens and has a sensitivity between 87% and 93%. Testing returned positive results for Streptococcus bovis subspecies pasteurianus Given its association with colorectal cancer, abdominal imaging and an endoscopic biopsy were performed, showing recurrent colonic malignancy. The patient underwent a right colon resection prior to cardiac intervention. This report describes the clinical application of the novel cell-free DNA Karius test, which led to the diagnosis of recurrent colon cancer associated with S. pasteurianus endocarditis.

Is It Useful to Repeat Blood Cultures in Endocarditis Patients? A Critical Appraisal

BACKGROUND

Previous guidelines for endocarditis have suggested repeating blood cultures until they become negative, with limited evidence.

METHODS

Literature reviews were conducted (1) on the incidence of persistent bacteremia and association with outcome and (2) on timing of valve culture negativization to examine the claim for prolongation of antibiotic therapy starting from negative blood cultures.

RESULTS

Persistent bacteremia and fever may be present in the first 3 days of endocarditis, despite treatment, and are more common in Staphylococcus (especially MRSA) and Enterococcus species. Persistent bacteremia (48-72 h), persistent infection (day 7), and new onset septic shock are related and predict in-hospital mortality. It is, however, persistent infection at day 7 and septic shock that primarily determine the infectious course of endocarditis, and not persistent bacteremia. Valve cultures at surgery become negative in most cases (>85-90%) after 14-21 days of antibiotic therapy, with no calculated benefit for prolonging therapy after 21 days.

CONCLUSIONS

Persistent infection at 7 days after appropriate antibiotic therapy is a better key event for prognosis then positive or negative blood cultures at 48-72 h. Therapy prolongation from the day of negative blood cultures is not reasonable. There is no need to survey blood cultures in endocarditis patients after starting therapy.

Streptococcus Mitis Endocarditis Associated with Early Gastric Carcinoma

We report a case of Streptococcus mitis endocarditis associated with early gastric carcinoma. A 71-year-old man who had been diagnosed with aortic regurgitation (AR) two years previously was referred for valve surgery and evaluation of elevated inflammatory markers. Four months previously, atrophic gastritis, early gastric adenocarcinoma, and colon polyp had been identified in the patient during endoscopy. However, Helicobacter pylori testing was negative. On admission, he had no dental diseases or recent oral procedures. Echocardiography demonstrated severe AR and mobile vegetation on the aortic valve. Magnetic resonance imaging revealed cerebral embolism and spondylodiscitis. Blood cultures grew Streptococcus mitis. At surgery, destruction of the left cusp with vegetation and a perforation of the non-coronary cusp were found; in addition, aortic valve replacement was performed. Although the association between Streptococcus bovis bacteremia and colon neoplasm is well recognized, the association between Streptococcus mitis endocarditis and gastrointestinal carcinoma should also be kept in mind.

Characterization of two lytic bacteriophages, infecting Streptococcus bovis/equinus complex (SBSEC) from Korean ruminant

Streptococcus bovis/equinus complex (SBSEC) is one of the most important lactic acid-producing rumen bacteria causing subacute ruminal acidosis. Despite the significance of the ruminal bacteria, lytic bacteriophages (phages) capable of infecting SBSEC in the rumen have been rarely characterized. Hence, we describe the biological and genomic characteristics of two lytic phages (designated as vB_SbRt-pBovineB21 and vB_SbRt-pBovineS21) infecting various SBSEC species, including the newly reported S. ruminicola. The isolated SBSEC phages were morphologically similar to Podoviridae and could infect other genera of lactic acid-producing bacteria, including Lactococcus and Lactobacillus. Additionally, they showed high thermal- and pH-stability, and those characteristics induce strong adaptation to the ruminal environment, such as the low pH found in subacute ruminal acidosis. Genome-based phylogeny revealed that both phages were related to Streptococcus phage C1 in the Fischettivirus. However, they had a lower nucleotide similarity and distinct genomic arrangements than phage C1. The phage bacteriolytic activity was evaluated using S. ruminicola, and the phages efficiently inhibited planktonic bacterial growth. Moreover, both phages could prevent bacterial biofilms of various SBSEC strains and other lactic acid-producing bacteria in vitro. Thus, the newly isolated two SBSEC phages were classified as new Fischettivirus members and could be considered as potential biocontrol agents against ruminal SBSEC bacteria and their biofilms.

Comparative Evaluation of Current Biochemical-, Sequencing-, and Proteomic-Based Identification Methods for the Streptococcus bovis Group

The Streptococcus bovis group (previously group D streptococci) consists of seven distinct species and subspecies. Definitive identification within the group is important, as certain organisms have been associated with gastrointestinal carcinoma, bacteremia, infective endocarditis, meningitis, biliary tract disease, and carcinoma, among others. Definitive identification, however, remains elusive due to limitations and inconsistencies across commonly used identification platforms in the United States. Here, we compared the performance of standard biochemical (Trek Gram-positive identification [GPID] plate, Vitek 2 GPID), sequencing (16S rDNA, sodA) databases (NCBI, RDP, CDC MicrobeNet), and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) platforms (Vitek MS, Bruker Biotyper MS) using a set of eight type strains representing all seven strains within the S. bovis group. Despite the evaluation of contemporary methods, no single platform was able to definitively identify all type strains within the S. bovis group. Vitek MS (85.7%, 7/8) provided the most accurate definitive identifications, followed by sodA sequencing (75%, 6/8). Vitek 2 and Bruker Biotyper RUO platforms performed the next best (62.5%, 5/8). All remaining platforms failed to adequately differentiate type strains within the S. bovis group (range, 0 to 37.5%). Laboratorians and clinicians should be aware of the identification limitations of routine testing algorithms and incorporate reflex testing, when appropriate, to platforms such as Vitek MS and/or sodA sequencing that are more able to definitively identify S. bovis group organisms. Further clinical evaluation was conducted using 65 clinical isolates from three geographically distinct U.S. institutions. Future improvements in identification platforms may reveal new clinical and epidemiological trends for members of the S. bovis group.

Platelet Activation and Aggregation Induced by Streptococcus bovis/Streptococcus equinus Complex

Streptococcus bovis/Streptococcus equinus complex (SBSEC) is a common cause of infective endocarditis (IE). For IE-pathogens, the capacity to activate and aggregate platelets is believed to be an important virulence mechanism. While the interactions between bacteria and platelets have been described in detail for many Gram-positive pathogens, little research has been carried out with SBSEC in this respect. Twenty-six isolates of the four most common species and subspecies of SBSEC identified in bacteremia were collected, and interactions with platelets were investigated in platelet rich plasma (PRP) from three donors. Aggregation was studied using light-transmission aggregometry and platelet activation using flow cytometry detecting surface upregulation of CD62P. Platelets and serum were treated with different inhibitors to determine mechanisms involved in platelet aggregation and activation. Twenty-two of 26 isolates induced aggregation in at least one donor, and four isolates induced aggregation in all three donors. In PRP from donor 1, isolate SL1 induced a rapid aggregation with a median time of 70 s to reach 50% aggregation. Blockade of the platelet Fc-receptor or enzymatic cleavage of IgG abolished platelet activation and aggregation. The capacity for bacteria-induced platelet aggregation was also shown to be transferable between donors through serum. SBSEC mediates platelet aggregation in an IgG and IgG-Fc-receptor dependent manner. Bacterial activation of platelets through this pathway is common for many bacteria causing IE and could be a potential therapeutic target for the prevention and treatment of this infection. IMPORTANCE The capacity of bacteria to activate and aggregate platelets is believed to contribute to the pathogenesis of IE. The Streptococcus bovis/Streptococcus equinus complex (SBSEC) contains known IE-pathogens, but there is limited research on the different subspecies ability to interact with platelets and what signaling pathways are involved. This study reports that 22 of 26 tested isolates of different subspecies within SBSEC can induce aggregation, and that aggregation is host dependent. The Fc-IgG-receptor pathway was shown essential for platelet activation and aggregation. To the best of our knowledge, this is the first study that reports on platelet interactions of SBSEC-isolates other than Streptococcus gallolyticus subspecies gallolyticus as well as the first study to report of mechanisms of platelet interaction of SBSEC-isolates. It adds SBSEC to a group of bacteria that activate and aggregate platelets via the platelet Fc-receptor. This could be a potential therapeutic target for prevention of IE.

Molecular Analysis With 16S rRNA PCR/Sanger Sequencing and Molecular Antibiogram Performed on DNA Extracted From Valve Improve Diagnosis and Targeted Therapy of Infective Endocarditis: A Prospective Study

BACKGROUND

Molecular analysis (MA) on heart valve (HV) improves the microbiologic diagnosis of infectious endocarditis (IE). The main drawback of MA is the lack of antimicrobial susceptibility information.

METHODS

We conducted a prospective cohort observational study of consecutive adult patients from April 2012 to May 2021 who underwent valve surgery at our hospital. The performance of MA, blood cultures (BC) and valve cultures (VC), and the diagnostic and therapeutic impact of MA were evaluated. Molecular antibiogram results were compared to culture-based antimicrobial susceptibility testing (AST).

RESULTS

A total of 137 patients with definite IE and 52 patients with no IE were enrolled in the study. Among IE cases BC, VC, and MA were positive in 75 (55%), 30 (22%), and 120 (88%) of IE cases, respectively. Among 62 cases of BC-negative IE (BCNE), 57 achieved diagnosis with MA. MA led to a change of antimicrobial therapy in 92% of BCNE. MA was negative in 100% of patients with no IE. Molecular antibiogram performed on 17 valve specimens that resulted positive for pathogens potential carrier of genes encoding for multidrug resistant mechanisms showed 100% concordance with AST.

CONCLUSIONS

MA showed a high specificity and sensitivity in etiological diagnosis of IE. Molecular antibiogram could overcome the major limitation of MA that is the lack of susceptibility testing. We advocate for the inclusion of MA among diagnostic criteria for IE and for a more extensive use of molecular antibiogram when the culture result is negative, and MA is the only positive test.

Streptococcus gallolyticus endocarditis on a prosthetic tricuspid valve: a case report and review of the literature

Background

Streptococcus gallolyticus subspecies gallolyticus is a known pathogen that causes infective endocarditis, and most cases involve the left heart valves. We present the first reported case of prosthetic tricuspid valve endocarditis caused by this microorganism. Relevant literature is reviewed.

Case presentation

A 67-year-old Jewish female with a history of a prosthetic tricuspid valve replacement was admitted to the emergency department because of nonspecific complaints including effort dyspnea, fatigue, and a single episode of transient visual loss and fever. No significant physical findings were observed. Laboratory examinations revealed microangiopathic hemolytic anemia and a few nonspecific abnormalities. Transesophageal echocardiogram demonstrated a vegetation attached to the prosthetic tricuspid valve. The involved tricuspid valve was replaced by a new tissue valve, and Streptococcus gallolyticus subspecies gallolyticus was grown from its culture. Prolonged antibiotic treatment was initiated.

Conclusions

Based on this report and the reviewed literature, Streptococcus gallolyticus should be considered as a rare but potential causative microorganism in prosthetic right-sided valves endocarditis. The patient’s atypical presentation emphasizes the need for a high index of suspicion for the diagnosis of infective endocarditis.

Disseminated Streptococcus bovis infection after consumption of manatee meat: A case report and review of the literature

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Disseminated S. bovis group infections are unusual in adults.

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S. bovis infections are usually related to colorectal neoplasia o biliary tract disease.

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S. bovis group zoonotic transmission could be biologically plausible, as infection in marine animals has been documented.

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No cases of S. bovis group have been published in relation to manatee ingestion.

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Wild animal consumption increases the risk of serious infections that could represent a hazard for public health.

Streptococcus bovis bacteremia (currently called S. gallolyticus) represents an infrequent condition, but associated with a high rate of morbidity and mortality Amado et al. (2015). The clinical presentation is characterized by symptoms associated with disseminated infection and with a higher frequency of endocarditis and gastrointestinal neoplasms, often occult Amado et al. (2015), Olmos et al. (2016). Probable sources of infection and zoonotic transmission have not been explored in the literature. We present a case of disseminated infection after ingestion of a marine mammal.

Referral for Colonoscopy in Patients with Streptococcus bovis Bacteremia and the Association with Colorectal Cancer and Adenomatous Polyps: A Quality Assurance Study

The association between Streptococcus bovis (S. bovis) bacteremia and colorectal cancer is well established. We aimed to review patients with S. bovis bacteremia at our local hospital system and determine the percentage of patients referred for colonoscopy. Methods: We searched the regional database to identify S. bovis-positive blood cultures from 2002 to 2016 and the clinical characteristics and outcomes of those patients. Results: A total of 86 patients with S. bovis bacteremia were identified. From the 86 patients, 14 were excluded. The mean age of the 72 remaining patients was 74.5 (SD 13), 42/72 (58%) were male, 12/72 (17%) had infective endocarditis, and 19 (26%) died during admission. Of the 53 patients who survived, 37 (70%) were referred for colonoscopy or CT colonography, of which 30 had a colonoscopy. Thus, 3/30 (10%) cases showed adenocarcinoma and 11/30 (37%) cases showed adenomatous polyps. Age, gender, or the presence of infective endocarditis were not associated with adenocarcinoma or adenomatous polyps. Discussion: In our local centers, a significant proportion of patients with S. bovis were found to have colon cancer or significant polyps, and thus the importance of referral to colonoscopy remains paramount.

Virulence of beta-hemolytic streptococci in infective endocarditis

BACKGROUND

Streptococci involved in infective endocarditis (IE) primarily comprise alpha- or non-hemolytic streptococci (ANHS). Moreover, beta-hemolytic streptococci (BHS) can be involved, and guidelines recommend the addition of gentamicin for the first 2 weeks of treatment and the consideration of early surgery in such cases. This study compared the morbidity and mortality associated with IE depending on the microorganisms involved (BHS, ANHS, staphylococci, and enterococci).

METHODS

We conducted a retrospective observational study between 2012 and 2017 in a single hospital in France. The endpoints were overall in-hospital mortality, 1-year mortality and the occurrence of complications.

RESULTS

We analyzed 316 episodes of definite IE including 150 (38%), 96 (25%), 46 (12%), and 24 cases (6%) of staphylococcal, ANHS, enterococcal, and BHS IE, respectively. In-hospital mortality was significantly higher in the staphylococcal (n = 40; 26.7%) and BHS groups (n = 6; 25.0%) than in the ANHS (n = 9; 9.4%) and enterococcal groups (n = 5; 10.9%) (all p < 0.01). The rates of septic shock and cerebral emboli were also higher in the BHS group than in the ANHS group [n = 7 (29.2%) vs. n = 3 (3.1%), p < 0.001; n = 7 (29.2%) vs. n = 12 (12.5%); p = 0.05, respectively].

CONCLUSION

This study confirmed that BHS IE has a more severe prognosis than ANHS IE. The virulence of BHS may be similar to that of staphylococci, justifying increased monitoring of these patients and more 'aggressive' treatments such as early surgery.

Investigating the association between African spontaneously fermented dairy products, faecal carriage of Streptococcus infantarius subsp. infantarius and colorectal adenocarcinoma in Kenya

Consumption of traditional fermented dairy products (tFDP) in Africa leads to the ingestion of up to 108Streptococcus infantarius subspecies infantarius (Sii) per millilitre of spontaneously fermented milk. Sii is a member of the Streptococcus bovis/Streptococcus equinus complex (SBSEC) for which some members are associated particularly with colorectal cancer or endocarditis. The extent of health risks to tFDP consumers is largely unknown. A hospital-based unmatched case-control study was conducted at Kenyatta National Hospital, Nairobi (Kenya) on 80 cases and 193 controls that were selected exhaustively from patients attending colonoscopy at the hospital. Logistic regression models adjusted for age, sex and residency were used in the statistical analysis. Consumption of tFDP was not associated with CRC (odds ratio (OR) 1.4; 95% Confidence interval (CI) 0.7-2.7; p=0.34). Risk factors associated with CRC included age above 40 years, and consumption of processed meat and alcohol. Faecal carriage of Sii was significantly higher in persons with colon tumours and polyps compared to controls (8.4% vs 21.6%: OR: 4.6; CI 1.3-15.9). Patients with haemorrhoids represented an unexpected carrier group with significantly higher Sii faecal carriage (30.4%, CI: 17.7-45.8). Consumption of tFDP does not represent risk factors for CRC whereas Sii seems to be associated with CRC. However, there is urgent need to assess this finding also in the general population, investigate the causality of SBSEC, Sii and CRC as well as compare the phylogenetic, functional and genomic relationship between human and dairy Sii with regards to the ongoing application of Sii in FDP production.

Tricuspid Valve Endocarditis due to Streptococcus bovis in a Patient with Ventricular Septal Defect: A Rare Manifestation-Case Report and Review of the Literature

Streptococcus bovis endocarditis has 18%-62% association with colonic neoplasms with multivalvular involvement and affects mainly elderly males leading to severe cardiac dysfunction, septic embolization, and neurological complications. The aortic valve is the commonest valve to be affected followed by aortic and mitral valves together. However, involvement of tricuspid valve is extremely rare. There are no reported cases of Streptococcus bovis endocarditis affecting the tricuspid valve in the presence of ventricular septal defect with left to right shunt. We report the case of a 25-year-old female with ventricular septal defect who was diagnosed to have tricuspid valve endocarditis caused by Streptococcus bovis. Her detailed colonoscopy, upper gastrointestinal endoscopy, liver biochemistry, and ultrasound scan of the abdomen were normal. She made a very good recovery with six weeks of intravenous antibiotics. This is the first case of tricuspid valve endocarditis caused by Streptococcus bovis in association with ventricular septal defect without any colonic lesions.

Clinically Occult Rectal Carcinoma Identified in a Case of Streptococcus bovis Endocarditis on Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography: A Case Report and Review of Literature

Numerous studies over past four decades have implicated a strong association of Streptoccus bovis infection with colorectal carcinomas. Strong is this association that a screening colonoscopy for identifying malignancy is considered mandatory in patients whose blood/fecal cultures show growth of this particular pathogen. Here, we report an interesting case of a 61-year-old female patient who presented with pyrexia of unknown origin for 3 weeks. Positron emission tomography/computed tomography, in addition to helping diagnose mitral valve endocarditis, also identified a clinically occult T2N0 rectal carcinoma.

Transcriptome analysis of Streptococcus gallolyticus subsp. gallolyticus in interaction with THP-1 macrophage-like cells

BACKGROUND

Streptococcus gallolyticus subsp. gallolyticus (S. gallolyticus) is a pathogen of infective endocarditis. It was observed previously that this bacterium survives longer in macrophages than other species and the phagocytic uptake by and survival in THP-1 macrophages is strain-dependent.

METHODS

The phagocytosis assay was performed with THP-1 macrophages. S. gallolyticus specific whole genome microarrays were used for transcriptome analysis.

RESULTS

Better survival in macrophages was observed for UCN34, BAA-2069 and ATCC43143 than for DSM16831 and LMG17956. S. gallolyticus strains show high resistance to tested bactericidal agents (acid, lysozyme and hydrogen peroxide). S. gallolyticus stimulates significant lower cytokine gene expression and causes less lysis of macrophages compared to the control strain Staphylococcus aureus. S. gallolyticus reacts to oxidative burst with a higher gene expression of NADH oxidase initially at the early phase. Expression of genes involved in D-alanylation of teichoic acid, carbohydrate metabolism and transport systems were upregulated thereafter.

CONCLUSION

S. gallolyticus is very resistant to bactericidal agents normally causing degradation of bacteria in phagolysosomes. Additionally, the D-alanylation of teichoic acid is an important factor for survival.