Recent developments in streptococcal taxonomy

Abstract

The classification of the streptococci has changed considerably in recent years, with the description of several new species, the re-naming of others, and the re-allocation of some former Streptococcus species to different genera. Phenotypic identification schemes have not kept pace with these taxonomic developments and there is considerable scope for improvement, perhaps with increased use of rapid enzyme-based methods involving fluorogenic or chromogenic substrates. Nucleic acid probes have been described for identification of several streptococcal species and the design of such probes has been greatly facilitated by the availability of 16S rRNA sequence data for most species. The pathogenic significance of some of the more recently described species is not fully understood. Many, if not all, of the oral streptococci appear to be involved in infective endocarditis, although not with equal frequency; several can also be a significant cause of infection in immunologically-compromised patients. Within the oral streptococci the ‘Streptococcus milleri group’ are frequently isolated from purulent infections and there is evidence for some specificity in the distribution of Streptococcus intermedius, S. constellatus and S. anginosus at different body sites. The S. mutans group are important aetiological agents in dental caries, and almost any of the oral streptococci may be involved in other infections in the mouth. In addition to the obvious need for more epidemiological data on the role of the newly described species in human and animal disease, further studies on their virulence mechanisms are also indicated.