Endocardiac infectivity and binding to extracellular matrix proteins of oral Abiotrophia species

Secretome analysis and virulence assessment in Abiotrophia defectiva

Background

Abiotrophia defectiva, although infrequently occurring, is a notable cause of culture-negative infective endocarditis with limited research on its virulence. Associated with oral infections such as dental caries, exploring its secretome may provide insights into virulence mechanisms. Our study aimed to analyze and characterize the secretome of A. defectiva strain CCUG 27639.

Methods

Secretome of A. defectiva was prepared from broth cultures and subjected to mass spectrometry and proteomics for protein identification. Inflammatory potential of the secretome was assessed by ELISA.

Results

Eighty-four proteins were identified, with diverse subcellular localizations predicted by PSORTb. Notably, 20 were cytoplasmic, 12 cytoplasmic membrane, 5 extracellular, and 9 cell wall-anchored proteins. Bioinformatics tools revealed 54 proteins secreted via the 'Sec' pathway and 8 via a non-classical pathway. Moonlighting functions were found in 23 proteins, with over 20 exhibiting potential virulence properties, including peroxiredoxin and oligopeptide ABC transporter substrate-binding protein. Gene Ontology and KEGG analyses categorized protein sequences in various pathways. STRING analysis revealed functional protein association networks. Cytokine profiling demonstrated significant proinflammatory cytokine release (IL-8, IL-1β, and CCL5) from human PBMCs.

Conclusions

Our study provides a comprehensive understanding of A. defectiva's secretome, laying the foundation for insights into its pathogenicity.

Abiotrophia defectiva endocarditis - Diagnostic and therapeutic challenge: Case report

Belonging to the normal oral, gastrointestinal, and urogenital flora, Abiotrophia defectiva is responsible for 1-2 % of all infective endocarditis (IE) cases. The manifestation of A.defectiva endocarditis may by atypical, without fever. Difficult to isolate pathogen requires special culture media. A 45-year-old female was admitted due to anemia and progressive weight loss (8 kg in 6 months). She had a history of benign mitral valve (MV) prolapse and non-stenotic bicuspid aortic valve (BAV). In echocardiography, large vegetations on MV and small vegetation on BAV were found. An enriched medium for fastidious pathogens was used. A. defectiva was identified using biochemical analysis with VITEK-2 Compact. In the fourth week of antibiotic therapy, she required urgent MV replacement due to MV regurgitation progression while vegetation on BAV disappeared. Although patient's frailty and underweight caused prolonged postoperative wound healing, she was transferred to rehabilitation in good conditions. No relapse of IE was observed during five-month follow-up.

Granulicatella adiacens as an Unusual Cause of Empyema: A Case Report and Review of Literature

Granulicatella adiacens , a nutritionally variant Streptococcus (NVS), is part of the normal commensal flora of human mouth, genital, and intestinal tracts and rarely causes disease. It has been mostly reported from bacteremia and endocarditis cases, but rarely can cause vertebral osteomyelitis, pancreatic abscess, otitis media, and endovascular, central nervous system, ocular, oral, bone and joint, and genitourinary infections. Due to requirement of fastidious culture conditions and non-specific colony morphology, serious diagnostic difficulties may arise in cases of NVS infections. Here, we are reporting a rare fatal infection of G. adiacens presented with empyema complicated to sepsis and necrotizing fasciitis.

Clinicians should be aware of the pathogenic potential of Granulicatella adiacens (a normal commensal flora of human mouth, genital and intestinal tracts). Appropriate supplemented media and a reliable detection system should be used to identify these fastidious organisms. We present this rare case to bring awareness among clinicians regarding such a rare but potentially fatal infection.

Abiotrophia defectiva Infective Endocarditis: A Rare and Dangerous Cause of Endocarditis

Infective endocarditis is an uncommon heart infection, typically involving heart valves. Abiotrophia defectiva is a rare cause of endocarditis, typically found within the GI tract, and is usually difficult to isolate and requires specialized media. We report a case of Abiotrophia defectiva endocarditis following a root canal.

Pyridoxine-Deficient Streptococcus: An Uncommon Virulent Cause of Subacute Destructive Aortic Valve Endocarditis

Nutritional variant streptococcus (NVS) or pyridoxal-dependent streptococcus is a rare but significant cause of infective endocarditis (IE), which presents as a diagnostic dilemma due to difficulty in organism isolation, and high rates of treatment failure, recurrence, and mortality. We discuss a case of a 52-year-old male who presented with chronic fatigue, cyclic fever, night sweats, and weight loss. He was treated with culture-directed antibiotics and surgical aortic valve replacement due to disease severity and risk of embolization. This case highlights the clinical significance of NVS IE, and the importance of early recognition, and immediate, often invasive therapy to improve outcomes.

Infective endocarditis caused by Abiotrophia defectiva presenting as anterior mitral leaflet perforation mimicking cleft anterior mitral leaflet

Infective endocarditis (IE) is primarily a bacterial infection of the heart valves. The most common organisms implicated include Staphylococcus and Streptococcus species. However, with the advent of MALDI-TOF and molecular techniques, the reports of IE being caused by rare organisms are on a rise. Here we describe a case of IE due to Abiotrophia defectiva. This is the first report of simultaneous infection of both mitral and aortic valves by Abiotrophia defectiva from India. IE caused by Abiotrophia defectiva has been seen to be more severe, associated with higher failure rates and relapse. This emphasizes the accurate identification of nutritionally variant Streptococcus (NVS) species as the management of choice varies between Abiotrophia and Granulicatella.

Double-Valve Heart Disease and Glomerulonephritis Consequent to Abiotrophia defectiva Endocarditis

Abiotrophia defectiva, a nutritionally deficient streptococcus, is a rare cause of infective endocarditis. It has been associated with hemophagocytic syndrome. We present the first case of A. defectiva infective endocarditis that led to antineutrophil cytoplasmic antibody-associated glomerulonephritis. The patient was a 55-year-old man whose endocarditis affected the mitral and aortic valves. His course was complicated by atrial fibrillation, stroke, and glomerulonephritis. He was successfully treated with antibiotics and dual valve replacement.

Contribution of different adherent properties of Granulicatella adiacens and Abiotrophia defectiva to their associations with oral colonization and the risk of infective endocarditis

Granulicatella adiacens (G. adiacens) and Abiotrophia defectiva (A. defectiva) colonize the oral cavity and form part of the normal flora in the intestinal and genitourinary tracts. As reported previously, the frequency of isolation of G. adiacens from the oral cavity was much higher than that of A. defectiva. However, it has been reported that compared with G. adiacens, A. defectiva was isolated at considerably higher frequencies from the blood of patients with infective endocarditis (IE). Hence, in this study, the in vitro interaction of G. adiacens and A. defectiva strains with host surfaces and biofilm formation was examined to assess whether their different adhesive properties contribute to their associations with oral colonization and IE, respectively. G. adiacens exhibited an increased binding ability to saliva-coated hydroxyapatite beads than A. defectiva following the addition of CaCl₂. Furthermore, biofilm formation was observed only for G. adiacens with the use of a polystyrene tube and scanning electron microscopy analysis. Conversely, A. defectiva displayed significantly greater adherence to human umbilical vein endothelial cells and immobilized fibronectin than G. adiacens. These findings suggest that differences in binding properties to host components imply specific binding mechanisms in G. adiacens and A. defectiva, which might mediate selective colonization in the oral cavity or are associated with the pathogenicity of endocarditis.

Native Valve Infective Endocarditis with Osteomyelitis and Brain Abscess Caused by Granulicatella adiacens with Literature Review

Granulicatella adiacens is a type of NVS (nutritionally variant streptococci) rarely causing infective endocarditis (IE). NVS are fastidious and unable to sustain growth on routine culture media due to lack of specific nutrients. Endocarditis caused by NVS due to their virulence is associated with higher treatment failures and mortality rates. New antimicrobial susceptibility patterns are indicative of a significant rise in penicillin resistance and susceptibility differences between NVS subspecies. Initial empirical therapy is essential as a delay in using the appropriate agent leads to poor results. We present a case of an immunocompetent young female with recent intravenous drug abuse resulting in native mitral valve endocarditis with ruptured chordae tendineae and septic embolization, causing brain abscess and lumbar spine osteomyelitis. She was transferred to a tertiary center where she underwent mitral valve replacement successfully and treated with six weeks of intravenous vancomycin and ertapenem. To our knowledge, ours is the first case report of G. adiacens endocarditis in an adult with brain abscess and osteomyelitis with an excellent response to antibiotic therapy. Based on our case report, literature review, and new antimicrobial susceptibility patterns, updates to treatment guidelines are suggested to improve the therapeutic outcomes.

Oral Microbiota: Microbial Biomarkers of Metabolic Syndrome Independent of Host Genetic Factors

The oral microbiota plays a critical role in both local and systemic inflammation. Metabolic syndrome (MetS) is characterized by low-grade inflammation, and many studies have been conducted on the gut microbiota from stool specimens. However, the etiological role of the oral microbiota in the development of MetS is unclear. In this study, we analyzed the oral and gut microbiome from 228 subgingival plaque and fecal samples from a Korean twin-family cohort with and without MetS. Significant differences in microbial diversity and composition were observed in both anatomical niches. However, a host genetic effect on the oral microbiota was not observed. A co-occurrence network analysis showed distinct microbiota clusters that were dependent on the MetS status. A comprehensive analysis of the oral microbiome identified Granulicatella and Neisseria as bacteria enriched in subjects with MetS and Peptococcus as bacteria abundant in healthy controls. Validation of the identified oral bacteria by quantitative PCR (qPCR) showed that healthy controls possessed significantly lower levels of G. adiacens (p = 0.023) and a higher ratio of Peptococcus to Granulicatella (p < 0.05) than MetS subjects. Our results support that local oral microbiota can be associated with systemic disorders. The microbial biomarkers identified in this study would aid in determination of which individuals develop chronic diseases from their MetS and contribute to strategic disease management.

A Case of Infective Endocarditis caused by Abiotrophia defectiva in Korea

Abiotrophia defectiva, a nutritionally variant streptococci can cause bacteremia, brain abscess, septic arthritis and in rare cases, infective endocarditis, which accounts for 5-6% of all cases. A. defectiva is characteristically difficult to diagnose and the mortality, morbidity and complication rates are high. Here, we discuss a case of infective endocarditis caused by A. defectiva. A 62-year-old female had previously undergone prosthetic valve replacement 6 years prior to admission. She developed infective endocarditis after tooth extraction. Her endocarditis was successfully treated with antimicrobial therapy and mitral valve replacement surgery. This is the first case of infective endocarditis caused by A. defectiva reported in Korea. This case shows that A. defectiva could be considered as a causative organism of infective endocarditis in Korea.

Infective endocarditis due to Abiotrophia defectiva and Granulicatella spp. complicated by infectious intracranial cerebral aneurysms: a report of three cases and review of the literature

Nutritionally variant streptococci, now classified as Abiotrophia defectivaor Granulicatella spp., are thought to account for 2 % of all infective endocarditis cases but estimates of their frequency are complicated by changes in nomenclature and difficulties in obtaining positive microbiology cultures. Their growth characteristics and difficulty undertaking antibiotic susceptibility testing may impede optimal antibiotic treatment decisions. We describe three patients with definite infective endocarditis due to these organisms seen at our hospital between 2005 and 2010, all of whom presented with neurological symptoms due to infectious intracranial cerebral aneurysms. We recommend that, for patients with left-sided infective endocarditis due to A. defictiva and Granulicatella spp., clinicians should consider imaging the central nervous system.

Granulicatella elegans endocarditis: a diagnostic and therapeutic challenge

A 63-year-old man with a history of non-ischaemic cardiomyopathy presented with acute worsening of heart failure and septic shock. Echocardiogram revealed a large aortic valve vegetation with new onset severe aortic incompetence. Blood cultures grew Granulicatella elegans, for which antimicrobial sensitivities could not be carried out in our lab. Despite antibiotic therapy and aggressive care, the patient's clinical condition worsened and he died. G. elegans, previously grouped under nutrient variant streptococci (NVS), is an extremely rare cause for bacterial infective endocarditis (IE). Unlike with the Viridans group, IE caused by NVS has a very poor outcome and higher mortality rate. The difficulty in isolation of the bacteria in culture, inability to reliably measure antibiotic susceptibility in vitro, frequent treatment failure and complications such as multivalvular involvement, make this an extremely challenging infection to treat. Early detection of the organism, appropriate antibiotics and early surgical management when indicated, are key to management.

Purification of a novel fibronectin binding protein from 'Granulicatella para-adiacens'

The interaction of microorganisms with fibronectin plays an important role in infective endocarditis. Characterization of fibronectin binding is not sufficient for nutritionally variant streptococci (NVS), which is an important pathogen associated with this disease. In this study, we identified and purified the novel fibronectin binding protein (FBP) by sonication and column chromatography from a ' Granulicatella para-adiacens' strain isolated from the oral cavity of a healthy donor. The purified molecule was located at the top of the gel in SDS-PAGE analysis, and heat treatment in the presence of sodium dodecyl sulfate resulted in its dissociation into smaller molecules. An anti-purified protein antibody was reacted with the topmost component of the sonic extract only from two ' G. para-adiacens' strains in Western blot analyses. Immunofluorescence staining indicated that the protein of interest was located on the cell surface of ' G. para-adiacens', but not on other NVS species. Bacterial adherence to fibronectin was inhibited by the purified FBP preparation. Optimum conditions for fibronectin binding of purified FBP were shown to be an NaCl concentration higher than 150 mM and a pH of c. 7.0. These results provide additional information for the elucidation of fibronectin binding by NVS.

Granulicatella infection: diagnosis and management

Granulicatella species, along with the genus Abiotrophia, were originally known as 'nutritionally variant streptococci'. They are a normal component of the oral flora, but have been associated with a variety of invasive infections in man and are most noted as a cause of bacterial endocarditis. It is often advised that Granulicatella endocarditis should be treated in the same way as enterococcal endocarditis. We review here the published data concerning diagnosis and treatment of Granulicatella infection, and include some observations from local cases, including four cases of endocarditis.

Identification and characterization of a fibronectin-binding protein from Granulicatella adiacens

The interaction of microorganisms with fibronectin plays an important role in infective endocarditis. Granulicatella adiacens is a member of the oral microbiota, formerly known as nutritionally variant streptococci, and is often isolated from endocarditis patients. In the present study we identified a surface protein, designated Cha, which binds to fibronectin, by a plaque hybridization procedure using the cshA sequence as probe, which encodes a fibronectin-binding molecule of Streptococcus gordonii DL1. The cha sequence was highly homologous to cshA and encoded a product of 2351 amino acid residues. The protein comprised a unique sequence in the N-terminal half region. The C-terminal region contained nine complete, and one incomplete, 115-amino acid residue repeat blocks. Among eight strains of nutritionally variant streptococci, three G. adiacens strains and one Abiotrophia defectiva strain carried the cha gene. Heterologous expression studies suggested that Cha adhered to immobilized fibronectin, and that this function was located in the unique region. Recombinant Cha protein also adhered to immobilize fibronectin and partially inhibited adherence of G. adiacens to fibronectin in a dose-dependent manner. These results suggest that Cha is a cell surface protein that mediates adherence of G. adiacens to fibronectin.

Abiotrophia defectiva infection of a total hip arthroplasty diagnosed by 16S rRNA gene sequencing

We describe a case of a total hip arthroplasty infection caused by Abiotrophia defectiva, identified by 16S rRNA gene sequencing. Removal of the prosthesis followed by antibiotic treatment resulted in a good clinical outcome. 16S rRNA gene sequencing can be a useful tool in diagnosing infection with this fastidious microorganism that can easily be misidentified using phenotypic identification methods.

Subarachnoid hemorrhage in a patient with Abiotrophia defectiva endocarditis

Endocarditis caused by Abiotrophia accounts for 5% of all cases of infective endocarditis (Roberts et al, Rev Infect Dis. 1979;1:955-66) and 5% to 6% of all cases of streptococcal endocarditis (Bouvet, Eur Heart J. 1995;16(suppl B):24-7; Brouqui et al, Clin Microbiol Rev. 2001;14:177-207). This endocarditis is associated with a high rate of embolization and treatment failure (Bouvet, Eur Heart J. 1995;16(suppl B):24-7). Neurological complications occur in 20% to 40% of all cases of infective endocarditis (Ossorio et al, Hosp Physician. 2003;39:21-4). Subarachnoid hemorrhage is a rare but devastating neurological complication. The authors presented a case of massive fatal subarachnoid hemorrhage in a patient with Abiotrophia defectiva endocarditis. To our knowledge, there are only 2 reported cases of mycotic aneurysms in Abiotrophia endocarditis, 1 of which was associated with subarachnoid hemorrhage (Leonard et al, N Engl J Med. 2001;344:233-4; Yang et al, Am J Med Sci. 2010;339:190-1).

Molecular bacterial diversity and bioburden of commercial airliner cabin air

Culture-independent, biomarker-targeted bacterial enumeration and identification strategies were employed to estimate total bacterial burden and diversity within the cabin air of commercial airliners. Samples from each of 4 flights on 2 commercial carriers were collected via air-impingement. The total viable microbial population ranged from below detection limits to 4.1 x 10(6) cells/m(3) of air, as assessed by the ATP assay. A gradual accumulation of microbes was observed from the time of passenger boarding through mid-flight, followed by a sharp decline in bacterial abundance and viability from the initiation of descent through landing. Representatives of the alpha-, beta-, and gamma-Proteobacteria, as well as Gram-positive bacteria, were isolated in varying abundance. Neisseria meningitidis rRNA gene sequences were retrieved in great abundance from Airline A followed by Streptococcus oralis/mitis sequences. Pseudomonas synxantha sequences dominated Airline B clone libraries, followed by those of N. meningitidis and S. oralis/mitis. The cabin air samples examined herein housed low bacterial diversity and were often dominated by a particular subset of bacteria: opportunistic pathogenic inhabitants of the human respiratory tract and oral cavity.

Experimental infective endocarditis induced by human supragingival dental plaque in rats

Human dental plaque is thought to contribute to disease, not only in the oral cavity but also at other body sites. To investigate the pathogenicity of dental plaque in tissues remote from the mouth, we examined the ability of human supragingival dental plaque to induce infective endocarditis (IE) in rats. In total, 15 out of 27 catheterized rats survived after intravenous injections with human supragingival dental plaque suspensions containing 3 x 10(6) colony-forming units (CFU) of bacterial cells. In surviving rats, infected vegetations were formed in all except one rat. The microbial composition of the infected vegetations was different from that of the respective dental plaque inocula, with Streptococcus oralis comprising the majority of the isolates. In rats affected with endocarditis, the aortic sinus was filled with fibrinous vegetation containing bacteria. Inflammatory cells infiltrated the aortic valve, the aorta adjacent to the valve, and the cardiac muscles. The inoculation of catheterized rats with a cell suspension of S. oralis isolate (5 x 10(6) CFU) was not lethal but capable of inducing endocarditis in all animals. The results suggest that if dental plaque were introduced into the bloodstream, it could serve as a potent source of bacteria causing IE in humans.

Granulicatella elegans native valve infective endocarditis: case report and review

Granulicatella elegans is a fastidious organism that is rarely implicated as a cause of infective endocarditis. Here, we describe a patient with mitral valve prolapse who developed G. elegans endocarditis. The organism was isolated from blood cultures and the patient had mitral valvuloplasty and repair, and completed a course of 6 weeks of intravenous antibiotics with no sequela.

Adherence of Abiotrophia defectiva and Granulicatella species to fibronectin: is there a link with endovascular infections?

During a 6-year period, we isolated three Abiotrophia defectiva, six Granulicatella adiacens and two G. 'para-adiacens' strains from clinical specimens. All A. defectiva strains were isolated from immunocompetent patients with endovascular infections, whereas the Granulicatella spp. strains were isolated from immunosuppressed patients with primary bacteremia. As the capacity of bacteria to adhere to the host extracellular matrix (ECM) has been implicated in the pathogenesis of endovascular infection, we investigated the ability of A. defectiva and Granulicatella spp. isolates to bind different ECM components immobilized in microtiter plates. Adherence tests showed a strong attachment of A. defectiva strains to fibronectin, whereas Granulicatella spp. strains were not adherent. The poor adherence of Granulicatella spp. strains to the ECM could be correlated with a lower propensity to induce endocarditis.

Catonella morbi and Granulicatella adiacens: new species in endodontic infections

OBJECTIVE

This study intended to examine samples from primary endodontic infections for the presence of Catonella morbi and Granulicatella adiacens, 2 species that have been recently suggested to be involved with infections in other oral sites.

STUDY DESIGN

Genomic DNA was isolated directly from samples taken from teeth with different forms of apical periodontitis, and a devised culture-independent 16S rRNA gene-based heminested PCR assay was used to determine the prevalence of these 2 target species. Species-specific primers were developed by aligning closely related 16S rRNA gene sequences. Species-specificity for each primer pair was confirmed by running PCR against a panel of oral bacteria and by sequencing of DNA from representative positive samples.

RESULTS

C morbi and G adiacens were detected in 33% and 19%, respectively, of the root canals associated with chronic apical periodontitis; 30% and 10%, respectively, of the cases diagnosed as acute apical periodontitis, and 16% and 11%, respectively, of the pus samples taken from acute apical abscesses. Overall, C morbi occurred in 26% and G adiacens in 14% of the samples taken from primary endodontic infections.

CONCLUSIONS

Our findings demonstrate that C morbi and G adiacens can take part in the microbiota associated with primary endodontic infections, and their specific role in the disease process warrants further elucidation.

Prosthetic valve endocarditis from Granulicatella adiacens (nutritionally variant streptococci)

Nutritionally variant streptococci (NVS) are an unusual but significant cause of endocarditis, with increased morbidity and mortality compared to those caused by enterococci or viridans streptococci. For many reasons, NVS endocarditis has remained very difficult to treat medically with antibiotics, and when the bacteria infect prosthetic valves, surgical intervention has historically been required to effect cure. We report the first case of Granulicatella adiacens prosthetic valve endocarditis (PVE) in a patient with congenital heart disease who was successfully treated with a regimen of vancomycin, gentamicin, and rifampin and provide the first review of the literature on NVS PVE, as well as discussion of logistics behind the use of this antibiotic regimen.

Infective endocarditis caused by Granulicatella elegans originating in the oral cavity

We studied the pheno- and genotypes of an oral Granulicatella elegans strain in comparison with those of a blood-derived isolate which caused infective endocarditis. The two isolates exhibited identical biochemical characteristics and had the same drug MICs. Their genotypes were indistinguishable, indicating that these were from the same clone. The transmission of G. elegans from the oral cavity thus should be noted as a possible cause of infective endocarditis.

Induction of immune response toStreptococcus pneumoniaeby administration of oral viridans streptococci via phosphorylcholine determinant

Expression of the phosphorylcholine (PC) epitope was examined in 48 viridans streptococcal strains, including Streptococcus pneumoniae R36a as the positive control, and their immunogenicity to induce an S. pneumoniae-cross-reactive response was evaluated in mice. Thirteen strains were found to express the PC epitope, while no obvious association was found between the taxonomic categories and PC expression. Serum antibody responses to S. pneumoniae cells were induced in mice by intraperitoneal injection of the PC-positive, but not PC-negative, strains. The cross-reactive antibodies induced by non-pneumococcal oral streptococci were readily inhibited by free hapten PC. IgM was the sole isotype of the anti-pneumococcal and anti-PC antibodies, and the phenomenon of immunological memory was not observed. Since the anti-PC antibody is critically important for resistance against pneumococcal infection in mice, the present results indicate the possibility that PC-expressing oral commensal bacteria have a significant influence on the hosts' responsiveness to S. pneumoniae.

Identification and characterization of bacterial-binding property in the type III repeat domain of fibronectin

To characterize fibronectin binding with Granulicatella adiacens, a causative agent of infective endocarditis, monoclonal antibodies were generated against human fibronectin and selected for their capacity to inhibit the fibronectin binding of the organism. Thermolysin and lysyl-endopeptidase digests of fibronectin were characterized by Western blot. The epitope of inhibitory monoclonal antibody was found in the central portion of fibronectin known as the cell-binding domain, and not in the N-terminal portion known to be the binding region of most microbial species, e.g., Staphylococcus aureus and Streptococcus pyogenes. While these two species could bind to both the N-terminal and central portion, Escherichia coli and G. adiacens bind only to the latter. Excess amounts of free fibronectin in the solution inhibited the bacterial adherence to the N-terminal fibronectin fragment, but not to the central region, thereby suggesting the central region plays a significant role for in vivo bacterial colonization in the presence of high concentrations of soluble fibronectin.

Aortitis in a child with Abiotrophia defectiva endocarditis

Abiotrophia defectiva, one of several nutritionally variant Streptococcus species, is an uncommon but important cause of endocarditis in children. We describe an unusual case complicated by extensive aortitis with pits in the ascending aorta and the proximal aortic arch.

Inhibition of fibronectin binding of some bacterial cells by subtle pH increase within the physiological range

The fibronectin (Fn)-binding ability of microorganisms is considered to be involved in their pathogenicities. Granulicatella adiacens, a member of the oral flora and a causative agent of culture-negative infective endocarditis, showed nearly maximum binding to immobilized Fn at pH 7.2 but greatly reduced binding at a slightly higher pH 7.4 and almost no binding at pH 7.6 in the presence of physiological concentration of NaCl (0.15 M). A similar pH-sensitive Fn-binding property was noted with Escherichia coli and Abiotrophia defectiva, but not with Streptococcus pyogenes nor Staphylococcus aureus. In contrast, bindings to laminin and fibrinogen observed for some of these strains were unaffected by the same pH changes. This fastidious pH-dependency of Fn-binding abilities of some bacteria warns that the pH condition must be seriously considered in the in vitro assay of bacterial adherence to fibronectin.

Serological properties of Abiotrophia and Granulicatella species (nutritionally variant streptococci)

Serological variations were examined among 12 type or reference strains and 91 oral isolates of vitamin B6-dependent Abiotrophia and Granulicatella spp. Rabbits were immunized with whole cells of 12 selected strains and 10 typing antisera were obtained, which were unreactive with the Lancefield group A to G antigen preparations. The reactivity of the antisera and autoclaved cell surface antigen extracts was tested by double diffusion in agar gel and a capillary precipitin test. These typing antisera categorized all Abiotrophia defectiva strains, all except one Granulicatella elegans strain, three-quarters of the Granulicatella adiacens, and half of the Granulicatella paraadiacens into 8 serotypes and 2 subserotypes. The Granulicatella balaenopterae type strain was unserotypable. All A. defectiva strains were serotype I, some of which were divided into subserotype I-1 and/or I-5. The G. adiacens strains generally belonged to serotype II or III, and the G. paraadiacens strains to serotype IV, V or VI. All G. adiacens or G. paraadiacens serotype II strains were also subserotype I-5. The G. elegans strains were serotype VII or VIII. These Abiotrophia and Granulicatella serotypes were undetectable among 33 strains of the other 11 species including the bacteriolytic enzyme-producing but vitamin B6-independent strains of Streptococcus, Enterococcus, Dolosigranulum and Aerococcus. The proposed serotyping system for Abiotrophia and Granulicatella spp. would be helpful in the identification and classification of these unique coccal isolates in ecological and epidemiological studies.