Recognizability of heterologous co-chaperones with Streptococcus intermedius DnaK and Escherichia coli DnaK

Streptococcus intermedius DnaK complements the temperature-sensitive phenotype of an Escherichia coli dnaK null mutant only when co-chaperones DnaJ and GrpE are co-expressed. Therefore, whether S. intermedius DnaK and E. coli DnaK can recognize heterologous co-chaperones in vitro was examined. Addition of heterologous GrpE to DnaK and DnaJ partially stimulated adenosine triphosphatase (ATPase) activity, and almost completely stimulated luciferase refolding activity. Addition of heterologous DnaJ to GrpE and DnaK also stimulated ATPase activity; however, significant luciferase refolding activity was not observed. Moreover, E. coli DnaJ had a negative effect on the luciferase refolding activity of the S. intermedius DnaK chaperone system. In E. coli chaperone mutants, with the exception of E. coli DnaJ, stronger expression of the heterologous co-chaperones partially or almost completely complemented the temperature-sensitive-phenotype. These results indicate that all heterologous co-chaperones can at least partially recognize DnaK of a distantly related species. A region of the ATPase domain that is present in the DnaK of gram-negative bacteria is absent from the DnaK of gram-positive bacteria. This region is believed to be important for recognition of co-chaperones from gram-negative bacteria. However, insertion of this segment into S. intermedius DnaK failed to increase its ability to recognize E. coli co-chaperones, implying that this region is unnecessary or insufficient for the recognition of E. coli co-chaperones. Thus, our data suggest that a basic structural similarity is conserved among the components of the S. intermedius and E. coli DnaK chaperone systems, allowing weak associations between heterologous components.

Rapid screening method for detecting highly pathogenic Streptococcus intermedius strains carrying a mutation in the lacR gene

Streptococcus intermedius is a member of the normal human commensal flora and secretes a human-specific cytolysin intermedilysin (ILY) as a major virulence factor. Expression of ily is repressed by LacR and loss-of-function mutations of LacR are observed in many ILY high-producing strains isolated from deep-seated abscesses, suggesting that high ILY production is necessary for increased virulence. However, because ILY exhibits no β-hemolysis on animal blood agar plates, differentiating ILY high- and low-producing strains using conventional laboratory methods is not possible. Interestingly, S. intermedius also produces glycosidases, including MsgA and NanA, which exhibit N-acetyl-β-d-glucosaminidase and neuraminidase activities, respectively. Moreover, MsgA expression, but not NanA, is negatively regulated by LacR. Here we measured the activities of MsgA, NanA and ILY in strains isolated from clinical specimens and dental plaque to determine the correlation between these glycosidase activities and ILY hemolytic activity. Hemolytic activity showed a strong positive correlation with MsgA and a weak negative correlation with NanA activities. Therefore, we calculated the ratio of MsgA and NanA activity (M/N ratio). This value showed a stronger positive correlation (r = 0.81) with ILY hemolytic activity and many strains with high M/N ratios (>2) were ILY-high producers with loss-of-function mutations in LacR.

Modulation of behaviour and virulence of a high alginate expressing Pseudomonas aeruginosa strain from cystic fibrosis by oral commensal bacterium Streptococcus anginosus

Cystic fibrosis (CF) airways harbour complex and dynamic polymicrobial communities that include many oral bacteria. Despite increased knowledge of CF airway microbiomes the interaction between established CF pathogens and other resident microbes and resulting impact on disease progression is poorly understood. Previous studies have demonstrated that oral commensal streptococci of the Anginosus group (AGS) can establish chronic pulmonary infections and become numerically dominant in CF sputa indicating that they play an important role in CF microbiome dynamics. In this study a strain of Pseudomonas aeruginosa (DWW2) of the mucoid alginate overproducing phenotype associated with chronic CF airway infection and a strain of the oral commensal AGS species Streptococcus anginosus (3a) from CF sputum were investigated for their ability to co-exist and their responses to biofilm co-culture. Bacteria in biofilms were quantified, pyocyanin expression by DWW2 was measured and the effect of AGS strain 3a on reversion of DWW2 to a non-mucoidal phenotype investigated. The virulence of DWW2, 3a and colony variant phenotypes of DWW2 in mono- and co-culture were compared in a Galleria mellonella infection model. Co-culture biofilms were formed in normoxic, hypercapnic (10% CO₂) and anoxic atmospheres with the streptococcus increasing in number in co-culture, indicating that these bacteria would be able to co-exist and thrive within the heterogeneous microenvironments of the CF airway. The streptococcus caused increased pyocyanin expression by DWW2 and colony variants by stimulating reversion of the mucoid phenotype to the high pyocyanin expressing non-mucoid phenotype. The latter was highly virulent in the infection model with greater virulence when in co-culture with the streptococcus. The results of this study demonstrate that the oral commensal S. anginosus benefits from interaction with P. aeruginosa of the CF associated mucoid phenotype and modulates the behaviour of the pseudomonad in ways that may be clinically relevant.

Environment and colonisation sequence are key parameters driving cooperation and competition between Pseudomonas aeruginosa cystic fibrosis strains and oral commensal streptococci

Cystic fibrosis (CF) patient airways harbour diverse microbial consortia that, in addition to the recognized principal pathogen Pseudomonas aeruginosa, include other bacteria commonly regarded as commensals. The latter include the oral (viridans) streptococci, which recent evidence indicates play an active role during infection of this environmentally diverse niche. As the interactions between inhabitants of the CF airway can potentially alter disease progression, it is important to identify key cooperators/competitors and environmental influences if therapeutic intervention is to be improved and pulmonary decline arrested. Importantly, we recently showed that virulence of the P. aeruginosa Liverpool Epidemic Strain (LES) could be potentiated by the Anginosus-group of streptococci (AGS). In the present study we explored the relationships between other viridans streptococci (Streptococcus oralis, Streptococcus mitis, Streptococcus gordonii and Streptococcus sanguinis) and the LES and observed that co-culture outcome was dependent upon inoculation sequence and environment. All four streptococcal species were shown to potentiate LES virulence factor production in co-culture biofilms. However, in the case of S. oralis interactions were environmentally determined; in air cooperation within a high cell density co-culture biofilm occurred together with stimulation of LES virulence factor production, while in an atmosphere containing added CO₂ this species became a competitor antagonising LES growth through hydrogen peroxide (H₂O₂) production, significantly altering biofilm population dynamics and appearance. Streptococcus mitis, S. gordonii and S. sanguinis were also capable of H2O2 mediated inhibition of P. aeruginosa growth, but this was only visible when inoculated as a primary coloniser prior to introduction of the LES. Therefore, these observations, which are made in conditions relevant to the biology of CF disease pathogenesis, show that the pathogenic and colonisation potential of P. aeruginosa isolates can be modulated positively and negatively by the presence of oral commensal streptococci.

The diversity of receptor recognition in cholesterol-dependent cytolysins

Cholesterol-dependent cytolysins (CDCs) are bacterial pore-forming toxins secreted mainly by pathogenic Gram-positive bacteria. CDCs generally recognize and bind to membrane cholesterol to create pores and lyse target cells. However, in contrast to typical CDCs such as streptolysin O, several atypical CDCs have been reported. The first of these was intermedilysin, which is secreted by Streptococcus intermedius and has human cell-specificity, human CD59 (huCD59) being its receptor. In the study reported here, the diversity of receptor recognition among CDCs was investigated and multi-receptor recognition characteristics were identified within this toxin family. Streptococcus mitis-derived human platelet aggregation factor (Sm-hPAF) secreted by S. mitis strain Nm-65 isolated from a patient with Kawasaki disease was previously shown to hemolyze erythrocytes in a species-dependent manner, its maximum activity being in human cells. In the present study, it was found that Sm-hPAF recognizes both membrane cholesterol and huCD59 as receptors for triggering pore-formation. Moreover, vaginolysin (VLY) of Gardnerella vaginalis showed similar characteristics to Sm-hPAF regarding receptor recognition. On the basis of the results presented here, the mode of receptor recognition of CDCs can be categorized into the following three groups: (i) Group I, comprising typical CDCs with high affinity to cholesterol and no or very little affinity to huCD59; (ii) Group II, including atypical CDCs such as ILY, with no or very little affinity to cholesterol and high affinity to huCD59; and (iii) Group III, which contains atypical CDCs such as Sm-hPAF and VLY with affinity to both cholesterol and huCD59.

A streptolysin S homologue is essential for β-haemolytic Streptococcus constellatus subsp. constellatus cytotoxicity

Streptococcus constellatus is a member of the Anginosus group streptococci (AGS) and primarily inhabits the human oral cavity. S. constellatus is composed of three subspecies: S. constellatus subsp. constellatus (SCC), S. constellatus subsp. pharyngis and the newly described subspecies S. constellatus subsp. viborgensis. Although previous studies have established that SCC contains β-haemolytic strains, the factor(s) responsible for β-haemolysis in β-haemolytic SCC (β-SCC) has yet to be clarified. Recently, we discovered that a streptolysin S (SLS) homologue is the β-haemolytic factor of β-haemolytic Streptococcus anginosus subsp. anginosus (β-SAA), another member of the AGS. Furthermore, because previous studies have suggested that other AGS species, except for Streptococcus intermedius, do not possess a haemolysin(s) belonging to the family of cholesterol-dependent cytolysins, we hypothesized that, as with β-SAA, the SLS homologue is the β-haemolytic factor of β-SCC, and therefore aimed to investigate and characterize the haemolytic factor of β-SCC in the present study. PCR amplification revealed that all of the tested β-SCC strains were positive for the sagA homologue of SCC (sagA(SCC)). Further investigations using β-SCC strain W277 were conducted to elucidate the relationship between sagA(SCC) and β-haemolysis by constructing sagA(SCC) deletion mutants, which completely lost β-haemolytic activity. This loss of β-haemolytic activity was restored by trans-complementation of sagA(SCC). Furthermore, a co-cultivation assay established that the cytotoxicity of β-SCC was clearly dependent on the presence of sagA(SCC). These results demonstrate that sagA(SCC) is the factor responsible for β-SCC β-haemolysis and cytotoxicity.

Intermedilysin Is Essential for the Invasion of Hepatoma HepG2 Cells byStreptococcus intermedius

Streptococcus intermedius causes endogenous infections leading to abscesses. This species produces intermedilysin (ILY), a human-specific cytolysin. Because of the significant correlation between higher ILY production levels by S. intermedius and deep-seated abscesses, we constructed ily knockout mutant UNS38 B3 and complementation strain UNS38 B3R1 in order to investigate the role of ILY in deep-seated infections. Strain UNS38 reduced the viability of human liver cell line HepG2 at infection but not of rat liver cell line BRL3A. Isogenic mutant strain UNS38 B3 was not cytotoxic in either cell line. Quantification of S. intermedius revealed that in infected HepG2 cells UNS38 but not UNS38 B3 increased intracellularly concomitantly with increasing cell damage. This difference between UNS38 and UNS38 B3 was not observed with UNS38 B3R1. Invasion and proliferation in BRL3A cells was not observed. Masking UNS38 or UNS38 B3R1 with ILY antibody drastically decreased adherence and invasion of HepG2. Moreover, coating strain UNS38 B3 with ILY partially restored adherence to HepG2 but without subsequent bacterial growth. At 1 day post-infection, many intact UNS38 were detected in the damaged phagosomes of HepG2 with bacterial proliferation observed in the cytoplasm of dead HepG2 after an additional 2 day incubation. These results indicate that surface-bound ILY on S. intermedius is an important factor for invasion of human cells by this bacterium and that secretion of ILY within host cells is essential for subsequent host cell death. These data strongly implicate ILY as an important factor in the pathogenesis of abscesses in vivo by this streptococcus.

Small heat shock protein AgsA: an effective stabilizer of enzyme activities

A small heat shock protein, AgsA, possesses chaperone activity that can reduce the amount of heat-aggregated protein in vivo, and suppress the aggregation of chemical- and heat-denatured proteins in vitro. Therefore, we examined the ability of AgsA to stabilize the activity of several enzymes by using this chaperone activity. We observed that AgsA can stabilize the enzymatic activities of Renilla (Renilla reniformis) luciferase, firefly (Photinus pyralis) luciferase, and β-galactosidase, and showed comparable or greater stabilization of these enzymes than bovine serum albumin (BSA), a well-known stabilizer of enzyme activities. In particular, AgsA revealed better stabilization of Renilla luciferase and β-galactosidase than BSA under disulfide bond-reducing conditions with dithiothreitol. In addition, AgsA also increased the enzymatic performance of β-galactosidase and various restriction enzymes to a comparable or greater extent than BSA. These data indicate that AgsA may be useful as a general stabilizer of enzyme activities.

Candida albicans strain-dependent modulation of pro-inflammatory cytokine release by in vitro oral and vaginal mucosal models

Candida albicans is a commensal organism at several sites and is a versatile, opportunistic pathogen. The underlying factors of pathogen and host associated with commensalism and pathogenicity in C. albicans are complex and their importance is largely unknown. We aimed to study the responses of oral epithelial (OEM) and vaginal epithelial models (VEM) to infection by oral and vaginal C. albicans strains to obtain evidence of inter-strain differences in pathogenicity and of site-specificity. Following inoculation of models, proinflammatory cytokines IL-1α, IL-1β, IL-6, IL-8 and prostaglandin E2 (PGE2) release were monitored and histological staining undertaken. Striking differences in strain behaviour and epithelial responses were observed. IL-1α, IL-1β and IL-8 release were significantly increased from the OEM in response to denture stomatitis strain NCYC 1467. Increased IL-8 release also followed infection of the OEM with both vaginal strains. Overall the VEM was relatively unresponsive to infection with either oral or vaginal strains under these conditions. Adherence and hyphal development were observed for all strains on both models although extensive, uniform tissue penetration was seen only with stomatitis strain NCYC 1467 on the OEM. Candidal strains were assayed for phospholipase (PL) and secreted aspartyl proteinase (SAP) activities where phospholipase (PL) activity was highest for strain NCYC 1467 although highest SAP activity was observed for vaginal strain NCPF 8112 in this assay. This is the first study to concurrently investigate cytokine production from oral and epithelial models using candidal strains originating from these respective mucosal sites from healthy and disease states. These data demonstrate significant differences in inflammatory responses of host epithelia to individual C. albicans strains.

The rag locus of Porphyromonas gingivalis contributes to virulence in a murine model of soft tissue destruction

The rag locus of Porphyromonas gingivalis encodes a putative TonB-dependent outer membrane receptor, RagA, and a 55-kDa immunodominant antigen, RagB. Inactivation of either ragA or ragB prevented expression of both RagA and RagB. Both the ragA and ragB mutants were significantly less virulent than wild-type strains in a murine model of infection.

Sequence diversity and antigenic variation at the rag locus of Porphyromonas gingivalis

The rag locus of Porphyromonas gingivalis W50 encodes RagA, a predicted tonB-dependent receptor protein, and RagB, a lipoprotein that constitutes an immunodominant outer membrane antigen. The low G+C content of the locus, an association with mobility elements, and an apparent restricted distribution in the species suggested that the locus had arisen by horizontal gene transfer. In the present study, we have demonstrated that there are four divergent alleles of the rag locus. The original rag allele found in W50 was renamed rag-1, while three novel alleles, rag-2 to rag-4, were found in isolates lacking rag-1. The three novel alleles encoded variants of RagA with 63 to 71% amino acid identity to RagA1 and each other and variants of RagB with 43 to 56% amino acid identity. The RagA/B proteins have homology to numerous Bacteroides proteins, including SusC/D, implicated in polysaccharide uptake. Monoclonal and polyclonal antibodies raised against RagB1 of P. gingivalis W50 did not cross-react with proteins from isolates carrying different alleles. In a laboratory collection of 168 isolates, 26% carried rag-1, 36% carried rag-2, 25% carried rag-3, and 14% carried rag-4 (including the type strain, ATCC 33277). Restriction profiles of the locus in different isolates demonstrated polymorphism within each allele, some of which is accounted for by the presence or absence of insertion sequence elements. By reference to a previously published study on virulence in a mouse model (M. L. Laine and A. J. van Winkelhoff, Oral Microbiol. Immunol. 13:322-325, 1998), isolates that caused serious disease in mice were significantly more likely to carry rag-1 than other rag alleles.

Development of a diagnostic PCR assay targeting the Mn-dependent superoxide dismutase gene (sodA) for identification of Streptococcus gallolyticus

A PCR-based assay to identify Streptococcus gallolyticus has been developed. The assay uses an oligonucleotide primer pair targeting a partial sequence of the manganese-dependent superoxide dismutase gene (sodA). The assay distinguished members of the S. gallolyticus group from other, closely related taxa successfully by yielding a 408-bp specific amplicon.

ARDRA and RAPD Analyses of Human and Animal Isolates of Streptococcus gallolyticus

A total of 23 Streptococcus gallolyticus strains, consisting of 12 strains from feces of healthy animals and 11 from clinical cases of human or cow mastitis milk, were examined genealogically. Four strains of S. bovis "biotype II/1" and 3 strains of S. equinus, the closely related organisms to S. gallolyticus, were also analyzed for outgroup comparison. Neither the amplified ribosomal DNA restriction analysis (ARDRA) nor the randomly amplified polymorphic DNA (RAPD) analysis that had been designed to recognize S. gallolyticus strains virulent in pigeons could differentiate clinical strains from the others of S. gallolyticus. No correspondence between the DNA profile in either analysis and the host animal species was detected.

Novel observation of hot-cold-hot hemolysis exhibited by group B streptococci

Six human isolates of group B streptococci (GBS) were cultured on blood agar anaerobically at 37 degrees C for 18 h and then at 4 degrees C for 6 h and reincubated anaerobically at 37 degrees C for 6 h. Three of the strains showed a marked enlargement of the hemolysis zone compared with that obtained after hot-only (37 degrees C for 18 h) or hot-cold (37 degrees C for 18 h and then 4 degrees C for 6 h) treatment. Subsequent broth culture experiments revealed that enhanced hemolytic activity due to hot-cold-hot treatment was observed in all 6 GBS strains when cultured in the presence of starch.

Re-evaluation of the taxonomic position of Streptococcus ferus

Streptococcus ferus was originally isolated from rats and, although it is often considered a member of the 'mutans group' streptococci on the basis of phenotypic criteria, its phylogenetic position has not been investigated. Here, the relationship of this organism to other streptococcal groups has been determined by DNA-DNA hybridization and by partial sequencing of 16S rDNA and the sodA gene. S. ferus was found to be distantly related to all currently described streptococci, with no strong evidence in support of its inclusion within any of the currently recognized streptococcal groups.

Effect on polymorphonuclear cell function of a human-specific cytotoxin, intermedilysin, expressed by Streptococcus intermedius

Streptococcus intermedius is a member of the normal flora of the mouth but is also an opportunistic pathogen associated with purulent infections at oral and nonoral sites. Intermedilysin (ILY) has been shown to be a cytolysin capable of generating pores in the cell membrane of erythrocytes demonstrable by electron microscopy. This effect has been shown to be specific for human cells. Since polymorphonuclear cells (PMNs) are the main cell involved in innate immunity we investigated the effect of purified intermedilysin from Streptococcus intermedius on PMN function. Active ILY at a concentration of 40 ng/microl caused a significant decrease in the number of intact PMNs after 60 min. The active cytolysin, when compared with heat-inactivated ILY, did not appear to be chemotactic for the PMNs but did cause an increase in intracellular calcium, with increased cell surface CD11b expression, metabolic burst, and phagocytosis of Staphylococcus aureus. These findings may have implications for the role of ILY in deep-seated abscesses.

Mannosidase production by viridans group streptococci

The production of mannosidase activity by all currently recognized species of human viridans group streptococci was determined using an assay in which bacterial growth was dependent on the degradation of the high-mannose-type glycans of RNase B and subsequent utilization of released mannose. RNase B is an excellent substrate for the demonstration of mannosidase activity since it is a glycoprotein with a single glycosylation site which is occupied by high-mannose-type glycoforms containing five to nine mannose residues. Mannosidase activity was produced only by some members of the mitis group (Streptococcus mitis, Streptococcus oralis, Streptococcus gordonii, Streptococcus cristatus, Streptococcus infantis, Streptococcus parasanguinis, and Streptococcus pneumoniae) and Streptococcus intermedius of the anginosus group. None of the other species within the salivarius and mutans groups or Streptococcus peroris and Streptococcus sanguinis produced mannosidase activity. Using matrix-assisted laser desorption ionization time-of-flight mass spectrometry, it was demonstrated that the Man(5) glycan alone was degraded while Man(6) to Man(9), which contain terminal alpha(1-->2) mannose residues in addition to the alpha(1-->3), alpha(1-->6), and beta(1-->4) residues present in Man(5), remained intact. Investigations on mannosidase production using synthetic (4-methylumbelliferone- or p-nitrophenol-linked) alpha- or beta-mannosides as substrates indicated that there was no correlation between degradation of these substrates and degradation of the Man(5) glycan of RNase B. No species degraded these alpha-linked mannosides, while degradation of the beta-linked synthetic substrates was restricted to strains within the Streptococcus anginosus, S. gordonii, and S. intermedius species. The data generated using a native glycoprotein as the substrate demonstrate that mannosidase production within the viridans group streptococci is more widely distributed than had previously been considered.

Antimicrobial effect of a novel ozone- generating device on micro-organisms associated with primary root carious lesions in vitro

The aims of this present study were (1) to assess the antimicrobial effect of ozone from a novel ozone-generating device (Heolozone, USA) [0.052% (v/v) in air delivered at a rate of 13.33 ml.s(-1)] on primary root carious lesions (PRCLs) and (2) to evaluate the efficacy of ozone specifically on Streptococcus mutans and Streptococcus sobrinus. In study 1, 40 soft PRCLs from freshly extracted teeth were randomly divided into two groups to test the antimicrobial effect on PRCLs from exposure to ozonated water for either 10 or 20 s. Half of a lesion was removed using a sterile excavator. Subsequently, the remaining lesion was exposed to the ozonised water for a period of either 10 or 20 s (corresponding to 0. 069 or 0.138 ml of ozone, respectively). Using paired Student t tests, a significant (p<0.001) reduction (mean +/- SE) was observed in the ozone-treated groups with either a 10-second (log(10) 3.57+/-0.37) or 20-second (log(10) 3.77+/-0.42) ozone application compared with the control groups (log(10) 5.91+/-0.15 and log(10) 6.18+/-0.21, respectively). In study 2, 40 sterile saliva-coated glass beads were randomly divided into two groups for each micro-organism. One glass bead was put into each bijou bottle with 3 ml of Todd-Hewitt broth. S. mutans and S. sobrinus were inoculated anaerobically overnight. Each glass bead was then washed with 2 ml of phosphate-buffered saline. Immediately, 10 s of ozone gas was applied to each glass bead in the test groups. There was a significant (p<0.0001) reduction (mean +/- SE) in ozone-treated samples for S. mutans (log(10) 1.01+/-0.27) and S. sobrinus (log(10) 1.09+/-0.36) compared with the control samples (log(10) 3.93+/-0.07 and log(10) 4.61+/-0.13, respectively). This treatment regime is an effective, quick, conservative and simple method to kill micro-organisms in PRCLs. Ozone gas application for a period of 10 s was also capable of reducing the numbers of S. mutans and S. sobrinus on saliva-coated glass beads in vitro.

Taxonomic study of "tufted mitior" strains of streptococci (Streptococcus sanguinis biotype 11); recognition of a new genospecies

The taxonomic position of tufted strains of streptococci, phenotypically resembling Streptococcus mitis and previously referred to as 'tufted mitior' was investigated. By 16S rRNA sequence analysis, it was clear that the "tufted mitior" strains belonged to the mitis group of species within the genus Streptococcus. It was confirmed that these strains were taxonomically independent at the species level, sharing less than 43%, DNA-DNA similarity with all established species of the mitis group. However biochemical test data obtained, using three commercial identification kits (Rapid ID32 Strep, STREPTOGRAM, and Biolog GP-plate) together with in-house biochemical tests employing 4-MUF-linked fluorogenic substrates did not reveal sufficient differential tests with which to identify the "tufted mitior" strains unequivocally. From these data, we conclude that these "tufted mitior" strains represent a new taxon within the mitis group of the genus Streptococcus, and propose that they should be considered as a genospecies until differential phenotypic characteristics are found for their identification.

Distribution of the intermedilysin gene among the anginosus group streptococci and correlation between intermedilysin production and deep-seated infection with Streptococcus intermedius

The distribution of intermedilysin, a human-specific cytolysin, among the anginosus group streptococci and the correlation of toxin production and infection by Streptococcus intermedius were investigated. PCR and Southern hybridization specific for the intermedilysin gene revealed that the toxin gene exists only in S. intermedius and no homologue to the toxin gene is distributed in S. anginosus and S. constellatus. Thus, the intermedilysin gene is useful as a marker gene of S. intermedius. Moreover, a human-specific hemolysis assay and Western blotting with intermedilysin-specific antibodies clearly demonstrated that the intermedilysin production level in isolates from deep-seated infections, such as brain and liver abscesses, is higher (6.2- to 10.2-fold, respectively) than in strains from normal habitats, such as dental plaque, or from peripheral infection sites. However, other candidate virulence factors of S. intermedius, such as chondroitin sulfate depolymerase, hyaluronidase, and sialidase activities, did not show such a clear correlation between enzymatic activity and isolation sites or disease severity. From these results, intermedilysin is likely to be the pathogenic or triggering factor of significance in inducing deep-seated infections with S. intermedius.

DNA-DNA reassociation studies of Streptococcus constellatus with unusual 16S rRNA sequences

DNA-DNA reassociation studies were performed on previously described 'CI strains', which form an unusual 16S rRNA population within the 'anginosus' group of Streptococcus. The CI strains displayed reassociation values of >70% with the Streptococcus constellatus NCDO 2226T strain, with Tm values <1 degrees C, indicating phylogenetic species identity.

A study of small-colony, beta-haemolytic, Lancefield group C streptococci within the anginosus group: description of Streptococcus constellatus subsp. pharyngis subsp. nov., associated with the human throat and pharyngitis

beta-Haemolytic, Lancefield group C streptococci within the anginosus-species group were shown by genetic and phenotypic criteria to be heterogeneous and to constitute two distinct taxa related at subspecies level to Streptococcus constellatus and Streptococcus anginosus, respectively. The first group, referred to here as DNA group 1, comprised six strains with 86-100% intragroup overall genomic DNA relatedness; five of the strains were originally isolated from the human throat and one was from an abdominal mass. They shared 61-77% DNA relatedness (delta Tm values = 1.2-1.5 degrees C) with reference strains of S. constellatus and were clearly differentiated from S. constellatus (now named Streptococcus constellatus subsp. constellatus) by the ability to produce beta-N-acetylgalactosaminidase, beta-N-acetylglucosaminidase, beta-D-fucosidase, beta-D-galactosidase and beta-D-glucosidase. The name S. constellatus subsp. pharyngis is proposed for these strains on the grounds that they are genetically and phenotypically distinct and exhibit a predeliction for the human throat, being isolated also from cases of pharyngitis. The DNA G + C content is 35-37 mol%. The type strain is MM9889aT (= NCTC 13122T). The second group (DNA group 2) was formed by five beta-haemolytic, Lancefield group C strains originally isolated from various human infections. DNA group 2 strains (81-100% intragroup DNA relatedness) shared 60-72% DNA relatedness (delta Tm values = 2.1-4.1 degrees C) with S. anginosus strains NCTC 10713T and MAS 283 but were not clearly differentiated phenotypically from S. anginosus, showed no clear pattern of clinical association, and therefore are not formally proposed as a new subspecies here.

PCR-Based methods for genotyping viridans group streptococci

Standard repetitive extragenic palindromic (REP)-PCR, enterobacterial repetitive intergenic consensus-PCR, and Salmonella enteritidis repetitive element-PCR methods for bacterial strain typing were performed with DNA extracted by boiling members of each of the currently recognized species of human viridans group streptococci. Each of the methods was reproducible. The unique isolates (n = 72) from 15 species of viridans group streptococci were readily distinguishable, with no two isolates showing greater than 90% per cent similarity. The majority of strains exhibited much less than 90% similarity. Isolates identical by REP-PCR were also identical by the other two methods. These PCR-based typing methods, although they do not permit determination of the species of the isolates, are simple to perform and are suitable for clinical and ecological investigations of viridans group streptococci.

Genetic approaches to the identification of the mitis group within the genus Streptococcus

The usefulness and reliability of partial sequence analysis of the manganese-dependent superoxide dismutase gene (sodA), autolysin (lytA) gene amplification and species-specific PCR based on the D-alanine:D-alanine ligase (ddl) gene for differentiating each member of the mitis group of the genus Streptococcus was investigated. On the phylogenetic tree based on sodA partial sequences (366 bp) from 96 strains, including all species currently within the mitis group isolated in different geographic areas (mainly Japan and the UK), eight well separated clusters were generated corresponding to recognized species, and all strains fell into those clusters to which they had also been assigned by DNA-DNA hybridization. The Streptococcus pneumoniae sub-cluster was located within the Streptococcus mitis cluster, but the sodA gene of S. pneumoniae was very conserved and therefore could be separated from all other species examined. Furthermore, the lytA gene amplification approach could also be used to differentiate S. pneumoniae from other species. The species-specific amplification product of the ddl gene was successfully detected in Streptococcus sanguinis and Streptococcus gordonii, but failed to be detected in some strains of Streptococcus oralis including the type strain and S. mitis. We conclude that the partial sequence analysis of the sodA gene could be applied globally as a reliable and easy method for the accurate identification of all species currently within the mitis group.

Current classification of the oral streptococci

The classification of the oral streptococci has long remained a difficult area of streptococcal taxonomy. This article reviews the current classification of these bacteria into four species groups, and each group is described in detail. The often confusing changes that have taken place in the classification, identification and nomenclature of the member species are reviewed against a historical background of gradually improving techniques and approaches, leading towards a natural classification based primarily on genotypic evidence. Identification schemes currently in use employing biochemical tests are also reviewed, together with alternative molecular approaches.

Occurrence of lipoteichoic acid in oral streptococci

The heterogeneous bacterial group known as oral streptococci was screened for the presence of cellular polyglycerolphosphate-containing lipoteichoic acid. This compound was detected in phenol extracts of lyophilized cells by an immunoassay in which polyglycerolphosphate-specific monoclonal antibody was used. Polyglycerolphosphate-containing lipoteichoic acid occurred in all 86 strains of oral streptococci examined except the Streptococcus mitis and Streptococcus oralis strains. This confirms the findings of Rosan (B. Rosan, Science 201:918-920, 1978) and Hamada et al. (S. Hamada, J. Mizuno, S. Kotani, and M. Torii, FEMS Microbiol. Lett. 8:93-96, 1980), is consistent with the results of the taxonomic study of oral streptococci performed by Kilian et al. (M. Kilian, L. Mikkelsen, and J. Henrichsen, Int. J. Syst. Bacteriol. 39:471-484, 1989), who emended the descriptions of Streptococcus sanguis, S. oralis, and S. mitis, and reflects the phylogenetic relationship among S. mitis, S. oralis, and Streptococcus pneumoniae.

Intermedilysin, a novel cytotoxin specific for human cells secreted by Streptococcus intermedius UNS46 isolated from a human liver abscess

A novel cytotoxin (intermedilysin) specific for human cells was identified as a cytolytic factor of Streptococcus intermedius UNS46 isolated from a human liver abscess. Intermedilysin caused human cell death with membrane blebs. Intermedilysin was purified from UNS46 culture medium by means of gel filtration and hydrophobic chromatography. The purified toxin was resolved into major and minor bands of 54 and 53 kDa, respectively, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These proteins reacted with an antibody against intermedilysin. Five internal peptide fragments of intermedilysin were sequenced and found to have 42 to 71% homology with the thiol-activated cytotoxin pneumolysin. However, the action of intermedilysin differed from that of thiol-activated cytotoxins, especially in terms of a lack of activation by dithiothreitol and resistance to treatments with N-ethylmaleimide and 5,5'-dithio-bis-(2-nitrobenzoic acid), although cholesterol inhibited the toxin activity. Intermedilysin was potently hemolytic on human erythrocytes but was 100-fold less effective on chimpanzee and cynomolgus monkey erythrocytes. Intermedilysin was not hemolytic in nine other animal species tested. Since human erythrocytes treated with trypsin were far less sensitive to intermedilysin than were the intact cells, a cell membrane protein(s) may participate in the intermedilysin action. These data demonstrated that intermedilysin is distinguishable from all known bacterial cytolysins.

Interactions between Eikenella corrodens and 'Streptococcus milleri-group' organisms: possible mechanisms of pathogenicity in mixed infections

Interactions between the 'Streptococcus milleri-group' organisms (SMG; S. intermedius, S. constellatus and S. anginosus) and Eikenella corrodens were investigated. Coaggregation reactions occurred frequently between S. anginosus (83% of strain combinations) or S. constellatus (87%) and E. corrodens isolates, but were infrequent between S. intermedius and E. corrodens (28%). No enhancement of enzyme activities against lipid, phosphate, peptide and saccharide substrates tested were detected with combinations of species in comparison to the species alone. Exponential growth of S. constellatus and S. intermedius, in mixed culture with E. corrodens, occurred within 6h post inoculation, in comparison to 25h without E. corrodens. No growth stimulation of S. anginosus was observed. It is concluded that both coaggregation and growth stimulation occur between E. corrodens and SMG isolates, and may be important mechanisms in the establishment of mixed infections involving these bacteria.

Genetic relatedness within and between serotypes of Streptococcus pneumoniae from the United Kingdom: analysis of multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, and antimicrobial resistance patterns

A collection of 54 isolates of invasive Streptococcus pneumoniae of serotypes 3 and 14 and serogroups 6, 9, 19, and 23 was investigated. Multilocus enzyme electrophoresis and pulsed-field gel electrophoresis suggested that two clones were represented in the collection, one of serotype 14 isolates, most of which were resistant to erythromycin, and one of serotype 9V isolates, in which resistance to penicillin (MIC, 1 microgram/ml), cefotaxime, and co-trimoxazole was common. Among other isolates there were only a limited correlation between genetic relatedness measured by multilocus enzyme electrophoresis and expression of the same capsule type. However, isolates with highly related pulsed-field gel electrophoresis patterns always shared the same serotype and highly related allele profiles. Calculation of the index of association suggests a freely recombining population structure with epidemic spread of successful clones.

Comparative efficacy of oral doses of clindamycin and erythromycin in the prevention of bacteraemia

Two antibiotics, clindamycin and erythromycin, were compared in a double-blind trial to test their efficacy in the prevention of post-dental extraction bacteraemia with streptococci in a group of 40 healthy patients. Tolerance to the oral doses was tested by questionnaire. Levels of drug in the serum were estimated using a microbiological assay. An in-vitro blood culture system was used as an analogy of the persistence of a bacteraemia in the presence of high levels of antibiotic. Isolates of streptococci were identified to species level. Minimum inhibitory concentrations of clindamycin and of erythromycin for each isolate were estimated. Results showed satisfactory levels of antibiotics in the blood for activity against oral streptococci. Clindamycin was slightly more effective than erythromycin in the prevention of post-extraction streptococcal bacteraemia but that efficacy was only 45%. Clindamycin as a single oral dose of 600 mg was well tolerated by patients compared with erythromycin 1.5 g.

Heterogeneity among 16S-23S rRNA intergenic spacers of species within the 'Streptococcus milleri group'

The 16S-23S rRNA intergenic spacer has been suggested as a suitable region of the bacterial genome from which to derive useful taxonomic information, particularly with regard to identification at the species level. To investigate this approach as an aid to the identification of the three species comprising the 'Streptococcus milleri group' (SMG), the spacers of isolates of Streptococcus intermedius, Streptococcus anginosus and Streptococcus constellatus were amplified by PCR and length polymorphisms determined by agarose gel electrophoresis. Phenotypically atypical isolates which had been identified presumptively as belonging to these three species were also included. Spacers from two representatives of each spacer length found within the three SMG species were sequenced. 16S-23S rRNA intergenic spacer length polymorphisms allowed discrimination between S. anginosus (350 bp or 450 bp amplification product) and S. constellatus (380 bp amplification product), species that are difficult to differentiate phenotypically. S. intermedius (330 bp or 450 bp amplification product) and S. anginosus (350 bp or 450 bp amplification product) were not reliably distinguished by this method but are phenotypically distinct. Sequencing data demonstrated that the spacers had a central region of highly variable length flanked by conserved regions which included a single tRNA(Ala) gene. Polymorphism in the length of the 16S-23S spacer determined by PCR provides a rapid and useful adjunct to strain identification for S. anginosus and S. constellatus, which are not readily differentiated phenotypically.

Effects of different acidulants on growth of 'Streptococcus milleri group' strains isolated from various sites of the human body

Growth of human clinical isolates of Streptococcus constellatus, Strep. intermedius and Strep. anginosus in HCl-, acetate and lactate acidified media was investigated. Under aerobic conditions, Strep. constellatus and Strep. anginosus were significantly more tolerant to all the acidulants than was Strep. intermedius. Under anaerobic conditions, Strep. anginosus and Strep. intermedius were significantly more tolerant to acetic acid (pH < 4.5) than Strep. constellatus.

Production of specific glycosidase activities by Streptococcus intermedius strain UNS35 grown in the presence of mucin

An isolate of Streptococcus intermedius from a brain abscess showed neuraminidase (sialidase), beta-D-galactosidase, N-acetyl-beta-D-glucosaminidase and N-acetyl-beta-D-galactosaminidase activities. The optimal pH values of these enzymes were 5.5-6.0, 5.5-6.0, 5.0-5.5 and 5.0-5.5, respectively. The km of the enzymes varied according to whether the type of substrate was chromogenic or fluorogenic; sialidase was most active at the lowest substrate concentrations, with a km of 0.01 mM. In semi-defined medium, with porcine gastric mucin--a model glycoprotein--as the sole source of fermentable carbohydrate, levels of the glycosidases were significantly increased. Addition of glucose to the mucin-containing medium, or growth of cells in media supplemented with glucose alone, repressed glycosidic activities and the majority of these were cell-associated. S. intermedius cells from cultures grown with mucin were able, simultaneously, to transport via sugar:phosphoenolpyruvate phosphotransferase (PTS) systems, monosaccharides which are constituents of carbohydrate side chains of glycoproteins. These cells also possessed significant levels of neuraminate-pyruvate lyase, involved in the intracellular catabolism of neuraminic acid; this was absent from cells grown with glucose. These mechanisms, collectively, may facilitate the persistence and growth of S. intermedius in vivo.

Activities of potential therapeutic and prophylactic antibiotics against blood culture isolates of viridans group streptococci from neutropenic patients receiving ciprofloxacin

All 47 sequential blood culture isolates of viridans group streptococci obtained from febrile neutropenic patients receiving quinolone prophylaxis were susceptible to vancomycin, teicoplanin, and imipenem. Resistance to benzylpenicillin (MIC for 50% of isolates [MIC50], 0.125 microgram/ml) and ceftazidime (MIC50, 4 micrograms/ml) was common. Most isolates were susceptible to amoxicillin, co-amoxiclav (amoxicillin-clavulanic acid at a 2:1 ratio by weight), azlocillin, clarithromycin, and erythromycin, with azithromycin showing comparable activity. The MIC90 of sparfloxacin was 1 microgram/ml; those for ciprofloxacin and ofloxacin were > 16 and 16 micrograms/ml, respectively.

Evolution of penicillin resistance in Streptococcus pneumoniae; the role of Streptococcus mitis in the formation of a low affinity PBP2B in S. pneumoniae

Penicillin-resistant strains of Streptococcus pneumoniae possess forms of penicillin-binding proteins (PBPs) that have a low affinity for penicillin compared to those from penicillin-sensitive strains. PBP genes from penicillin-resistant isolates are very variable and have a mosaic structure composed of blocks of nucleotides that are similar to those found in PBP genes from penicillin-sensitive isolates and blocks that differ by up to 21%. These chromosomally encoded mosaic genes have presumably arisen following transformation and homologous recombination with PBP genes from a number of closely related species. This study shows that PBP2B genes from many penicillin-resistant isolates of S. pneumoniae contain blocks of nucleotides originating from Streptococcus mitis. In several instances it would appear that this material alone is sufficient to produce a low affinity PBP2B. In other examples PBP2B genes possess blocks of nucleotides from S. mitis and at least one additional unidentified species. Mosaic structure was also found in the PBP2B genes of penicillin-sensitive isolates of S. mitis or S. pneumoniae. These mosaics did not confer penicillin resistance but nevertheless reveal something of the extent to which localized recombination occurs in these naturally transformable streptococci.

Species of alpha-hemolytic streptococci possessing a C-polysaccharide phosphorylcholine-containing antigen

An enzyme-linked immunosorbent assay technique was used to detect and quantify C-polysaccharide-like antigen in strains of alpha-hemolytic streptococci classified into species by following the latest taxonomic recommendations. C-polysaccharide-like antigen is found only in Streptococcus oralis, S. mitis, and S. pneumoniae, which are genetically closely related.

Chondroitin sulfate depolymerase and hyaluronidase activities of viridans streptococci determined by a sensitive spectrophotometric assay

Sensitive spectrophotometric assays for the detection of bacterial chondroitin sulfate depolymerase and hyaluronidase activities were developed by using Stains-all (1-ethyl-2-[3-(1-ethylnaphtho-[1,2-d]thiazolin-2-ylidene)-2- methylpropenyl]naphtho-[1,2-d]thiazolium bromide). Stains-all interacts with hyaluronic acid to produce a shift in the absorption spectrum with a distinct absorption peak between 620 and 660 nm, while chondroitin sulfate interacts to form a distinct shoulder between 440 and 500 nm. Assays measure undegraded substrate. A collection of 110 strains of viridans streptococci, including representatives of all the currently recognized species, was studied. Streptococcus intermedius and S. constellatus degraded hyaluronic acid, while only strains of S. intermedius, primarily isolated from brain and liver abscesses, produced chondroitin sulfate depolymerase. S. intermedius, of all the viridans streptococci, produces the widest range of glycoprotein- and glycosoaminoglycan-degrading enzymes, which may contribute to the virulence of this species.

A numerical taxonomic study of the "Streptococcus milleri" group based upon conventional phenotypic tests and pyrolysis mass spectrometry

Clinical strains presumptively identified as Streptococcus milleri (60), and blind coded collection strains (21) were characterised in conventional tests and pyrolysis mass spectrometry. Comparison of the clusters found by these two approaches revealed five clearly distinct centres of variation. Three corresponded to the DNA homology groups suggested by Whiley and Hardie (1989) as representing the species S. anginosus, S. intermedius and S. constellatus; a fourth comprised three Lancefield group C beta-haemolytic strains; the fifth may represent a biotype of S. anginosus. The characteristics of the latter group are described.

Streptococcus intermedius, Streptococcus constellatus, and Streptococcus anginosus (the Streptococcus milleri group): association with different body sites and clinical infections

The associations of Streptococcus intermedius, S. constellatus, and S. anginosus (the three species of the S. milleri group) with clinical infections and sites of isolation were investigated by using a simple biochemical scheme to identify a collection of 153 clinical isolates. S. intermedius was associated with abscesses of the brain and liver, while both S. anginosus and S. constellatus were isolated from a wider range of sites and infections. S. anginosus strains predominated in both genitourinary and gastrointestinal sources and exhibited a wider range of phenotypes, particularly in the ability to ferment mannitol and/or raffinose.

A scheme for the identification of viridans streptococci

A collection of strains representing all the currently recognised species of oral or viridans streptococci (Streptococcus sanguis, S. parasanguis, S. gordonii, S. oralis, S. mitis, S. salivarius, S. vestibularis, S. anginosus, S. constellatus, s. intermedius, S. mutans and S. sobrinus) were tested for the production of a range of glycosidase activities with 4-methylumbelliferyl-linked fluorogenic substrates, and for reactions in a range of conventional fermentation and hydrolytic tests. The resulting biochemical scheme, consisting of 14 tests, enabled the differentiation of all these species and distinguished three biotypes within S. sanguis. The scheme reported here represents an improvement over currently available schemes for the identification of viridans streptococci.

Streptococcus crista sp. nov., a viridans streptococcus with tufted fibrils, isolated from the human oral cavity and throat

We studied strains of an unusual streptococcus that superficially resembles Streptococcus sanguis but has fibrils that are arranged in lateral tufts. These strains were originally isolated from human throats and oral cavities and have been referred to previously as "Streptococcus sanguis I," the "CR group," and the "tufted-fibril group." Until now, insufficient phenotypic data have been available to allow reliable differentiation of these strains from other viridans streptococcal species, particularly the species in the S. sanguis group. Recently, workers have proposed a scheme of phenetic tests that is based on 4-methylumbelliferyl-linked substrates and conventional biochemical tests and allows the tufted-fibril group to be differentiated; these organisms differ from other viridans species in being able to hydrolyze arginine but not esculin and in producing alpha-L-fucosidase but not beta-glucosidase or alkaline phosphatase. These data, together with the results of our DNA-DNA hybridization experiments and the unusual ultrastructure of the tufted-fibril strains as determined by electron microscopy, demonstrate that these organisms represent a new species, for which the name Streptococcus crista is proposed. The DNA base composition is 42.6 to 43.2 mol% G + C. The type strain is strain CR311 (= NCTC 12479).

Conservation of the gene encoding streptococcal antigen I/II in oral streptococci

The spaP gene of Streptococcus mutans serotype c encodes a major cell surface protein, streptococcal antigen (SA) I/II, with an Mr of 185,000, that is thought to be involved in bacterial adhesion to teeth. Proteins with significant amino acid sequence homology to SA I/II have also been found in S. sobrinus and S. sanguis. The objectives of this study were to investigate the conservation of the spaP gene in the mutans groups of streptococci and to determine whether homologous genes were present in other species of alpha-hemolytic streptococci. DNA extracted from representative strains of 19 streptococcal species was examined by Southern hybridization and partial DNA sequence analysis. A series of five overlapping DNA probes from the spaP gene were amplified by the polymerase chain reaction and used in the Southern hybridizations. The entire gene was found to be well conserved in all strains of S. mutans serotypes c, e, and f investigated. A probe from the 3' region of the gene, which encodes residues 857 to 1207 of the SA I/II protein, hybridized with DNA from a number of mutans streptococci, as well as with DNA from nonmutans alpha-hemolytic streptococci. Conservation within this region was further demonstrated by sequencing gene fragments of two strains of S. intermedius and S. oralis. The results show that some regions of the spaP gene are highly conserved not only in the mutans group of streptococci but also in other nonmutans alpha-hemolytic streptococci. This suggests that a family of cell surface proteins which, by analogy with the 185,000-Mr SA I/II of S. mutans, could be involved in bacterial adhesion might exist.

A simple biochemical scheme for the differentiation of Streptococcus mutans and Streptococcus sobrinus

A collection of wild-type and reference strains of Streptococcus mutans and Streptococcus sobrinus was compared using a set of fermentation and enzymic tests in order to establish a simple scheme for the differentiation of these two species isolated from selective media. Tests for the production of acid from N-acetylglucosamine, arbutin and melibiose, and the presence of alpha-galactosidase and alpha-glucosidase activities were useful in differentiating these species. Strains of Streptococcus mutans unable to ferment melibiose were also frequently unable to ferment other sugars; a consideration of the genetic control and organization of the genes involved in melibiose metabolism indicates that certain of the conventional characterization tests are not measurements of independent biochemical capabilities.

Emended descriptions and recognition of Streptococcus constellatus, Streptococcus intermedius, and Streptococcus anginosus as distinct species

Strains currently classified as Streptococcus anginosus include strains previously identified as Streptococcus constellatus (Prevot 1924) Holdeman and Moore 1974, Streptococcus intermedius (Prevot 1925), and "Streptococcus milleri" (Guthof 1956) because these specific epithets were argued to be later synonyms of Streptococcus anginosus (Andrewes and Horder 1906) Smith and Sherman 1938 by Coykendall et al. (Int. J. Syst. Bacteriol. 37:222-228, 1987). However, recent data from DNA-DNA hybridization experiments, whole-cell-derived polypeptide patterns determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and data from phenotypic testing have demonstrated that Streptococcus anginosus strains represent three readily identifiable taxa to which the previously assigned type strains of Streptococcus constellatus (strain NCDO 2226 [= ATCC 27823], Streptococcus intermedius (strain NCDO 2227 [= ATCC 27335], and Streptococcus anginosus (strain NCTC 10713 [= ATCC 33397] have been shown to belong. Therefore, we propose recognition of Streptococcus constellatus (emend.) (type strain NCDO 2226 [= ATCC 27823]), Streptococcus intermedius (emend.) (type strain NCDO 2227 [= ATCC 27335]), and Streptococcus anginosus (emend.) (type strain NCTC 10713 [= ATCC 33397]) as distinct species and propose an emended description of each of these taxa.