For millions of years, our resident microbes have coevolved and coexisted with us in a mostly harmonious symbiotic relationship. We are not distinct entities from our microbiome, but together we form a 'superorganism' or holobiont, with the microbiome playing a significant role in our physiology and health. The mouth houses the second most diverse microbial community in the body, harbouring over 700 species of bacteria that colonise the hard surfaces of teeth and the soft tissues of the oral mucosa. Through recent advances in technology, we have started to unravel the complexities of the oral microbiome and gained new insights into its role during both health and disease. Perturbations of the oral microbiome through modern-day lifestyles can have detrimental consequences for our general and oral health. In dysbiosis, the finely-tuned equilibrium of the oral ecosystem is disrupted, allowing disease-promoting bacteria to manifest and cause conditions such as caries, gingivitis and periodontitis. For practitioners and patients alike, promoting a balanced microbiome is therefore important to effectively maintain or restore oral health. This article aims to give an update on our current knowledge of the oral microbiome in health and disease and to discuss implications for modern-day oral healthcare.

The prevention and treatment of periodontal diseases appear to be crucial for the prevention of bacteremia associated with oral procedures.

A collection of 426 Haemophilus strains isolated from people with infectious diseases and from the normal flora of mucous membranes in humans and various animal species was studied in an attempt to revise and improve the taxonomy of the genus Haemophilus. The examinations included the determination of a number of biochemical and physiological properties, of which several had not previously been applied to the taxonomy of haemophili. The resulting data revealed many hitherto unrecognized characters of taxonomic significance, and several of the species can now be more accurately defined. The classification presented is supported by the DNA base composition of a large number of representative strains. A diagnostic key to the different taxa is presented. Haemophilus injluenzae and H. paruinfluenzae have been subdivided into a number of biotypes. It is possible to demonstrate a relationship between the individual biotypes of H. influenzae and the origin of the strains assigned to them. The results indicate that H. aegyptius, H. parahaemolyticus and H. paraphrohaemolyticus do not merit specific status. Four unnamed taxa of V-factor-dependent haemophili have been recognized. The name Haemophilus segnis is proposed for one of these taxa, which consists mainly of strains isolated from the human oral cavity. It is demonstrated that the name H. ducreyi has been used for different groups of bacteria, and that only one of these groups can legitimately be assigned to the genus Haemophilus. Haemolytic V-factor-dependent strains from swine, previously included in H. parahaemolyticus, are significantly different from strains of human origin and should be named H.pleuropneumoniae. None of the strains from swine and fowls were haemindependent. The relationships of these strains to the species H. suis and H. gallinarum, and to H. parasuis and H. paragallinarum are discussed. Haemophilus piscium is shown not to belong to the genus Haemophilus. The taxonomic position of H. aphrophilus is uncertain and its possible relationship to Actinobacillus actinomycetemcomitans requires further study. The positive correlation found between the ecology of the strains studied and their affiliation with the different taxa is discussed.

No abstract

The human serum immunoglobulins IgG and IgA1 are produced in bone marrow and both interact with specific cellular receptors that mediate biological events. In contrast to IgA1, the glycosylation of IgG has been well characterized, and its interaction with various

The involvement of Propionibacterium acnes in the pathogenesis of acne is controversial, mainly owing to its dominance as an inhabitant of healthy skin. This study tested the hypothesis that specific evolutionary lineages of the species are associated with acne while others are compatible with health. Phylogenetic reconstruction based on nine housekeeping genes was performed on 210 isolates of P. acnes from well-characterized patients with acne, various opportunistic infections, and from healthy carriers. Although evidence of recombination was observed, the results showed a basically clonal population structure correlated with allelic variation in the virulence genes tly and camp5, with pulsed field gel electrophoresis (PFGE)- and biotype, and with expressed putative virulence factors. An unexpected geographically and temporal widespread dissemination of some clones was demonstrated. The population comprised three major divisions, one of which, including an epidemic clone, was strongly associated with moderate to severe acne while others were associated with health and opportunistic infections. This dichotomy correlated with previously observed differences in in vitro inflammation-inducing properties. Comparison of five genomes representing acne- and health-associated clones revealed multiple both cluster- and strain-specific genes that suggest major differences in ecological preferences and redefines the spectrum of disease-associated virulence factors. The results of the study indicate that particular clones of P. acnes play an etiologic role in acne while others are associated with health.

We examined a collection of 151 strains of the viridans type of streptococci, which were isolated mainly from human oral cavities and included several reference strains, in an attempt to revise and improve the taxonomy of this group of bacteria. Our examinations included determinations of a high number of biochemical and physiological characteristics and serological reactivity. The resulting data revealed several hitherto unrecognized characters of taxonomic significance, and several of the species can now be more accurately defined. A diagnostic key to the taxa is presented. Strains previously identified as Streptococcus sanguis could be divided into two clearly distinct species, Streptococcus sanguis sensu strict0 (type strain, ATCC 10556) and a new species, Streptococcus gordonii (type strain, ATCC 10558). Streptococcus rnitis was divided into two biovars, consisting of strains possessing group 0 antigens and strains possessing group K antigen. The group of strains assigned to Streptococcus anginosus was biochemically and serologically heterogeneous, but the data did not allow natural subdivisions. Based on the results of this study, emended descriptions of the species Streptococcus oralis, S. rnitis, and S . sanguk are provided. The classification resulting from this study is in complete agreement with previously published genetic data.The viridans type of streptococci encountered in oral cavities and pharynges have been curiously refractory to satisfactory classification. Although several comprehensive taxonomic studies have been performed (3, 5, 8, 11, 22, 25, 41, 42, 49), international consensus on classification and nomenclature has not been obtained. As a consequence, several synonyms have been applied to the same organisms (18, 24, 29). Furthermore, several of the species are genetically heterogeneous (12, 13). However, lack of distinguishing phenotypic traits has left these problems unsolved. There is no doubt that this situation has hampered a clear understanding of the ecology of these bacteria and of some of the molecular mechanisms involved in plaque formation on teeth.The Approved Lists of Bacterial Names published in 1980 (43) included, in addition to some of the "mutans" species, the following six species of streptococci normally encountered in oral cavities: Streptococcus sanguis, Streptococcus mitis, Streptococcus salivarius, Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius. Subsequently, Coykendall et al. (14) demonstrated that the last two names, together with the name "Streptococcus rnilleri," which is used mainly in European laboratories, are later synonyms of S. anginosus. Other workers have found that S. constellatus is sufficiently distinct from S. anginosus to warrant specific recognition (26).The name bbStreptococcus mitior" has been used mainly by workers in European laboratories for streptococci that lack the ability to hydrolyze arginine and esculin and may or may not produce extracellular polysaccharide. Although an overwhelming amount of data, ...

Streptococcus pneumoniae is a member of the Mitis group of streptococci which, according to 16S rRNA-sequence based phylogenetic reconstruction, includes 12 species. While other species of this group are considered prototypes of commensal bacteria, S. pneumoniae is among the most frequent microbial killers worldwide. Population genetic analysis of 118 strains, supported by demonstration of a distinct cell wall carbohydrate structure and competence pheromone sequence signature, shows that S. pneumoniae is one of several hundred evolutionary lineages forming a cluster separate from Streptococcus oralis and Streptococcus infantis. The remaining lineages of this distinct cluster are commensals previously collectively referred to as Streptococcus mitis and each represent separate species by traditional taxonomic standard. Virulence genes including the operon for capsule polysaccharide synthesis and genes encoding IgA1 protease, pneumolysin, and autolysin were randomly distributed among S. mitis lineages. Estimates of the evolutionary age of the lineages, the identical location of remnants of virulence genes in the genomes of commensal strains, the pattern of genome reductions, and the proportion of unique genes and their origin support the model that the entire cluster of S. pneumoniae, S. pseudopneumoniae, and S. mitis lineages evolved from pneumococcus-like bacteria presumably pathogenic to the common immediate ancestor of hominoids. During their adaptation to a commensal life style, most of the lineages gradually lost the majority of genes determining virulence and became genetically distinct due to sexual isolation in their respective hosts.