Novel observations of genotypic and metabolic characteristics of three subspecies of Streptococcus gallolyticus.

Abstract

Streptococcus gallolyticus is often found as a normal member of the gut microflora of various animals, while it has been reported to cause mastitis in cattle, septicemia in pigeons, and meningitis, sepsis, and endocarditis in humans (2). The species, which includes strains formerly identified as Streptococcus bovis biotye I and S. bovis biotype II/2, can be distinguished from other related taxa or biotypes (i.e., Streptococcus equinus and S. bovis biotype II/1) based on the results of DNA-DNA reassociation experiments (3). Recently, Schlegel et al. (6) demonstrated that S. gallolyticus, S. bovis biotype II/2, Streptococcus macedonicus, and Streptococcus waius form a single DNA cluster and thus proposed S. gallolyticus subsp. gallolyticus subsp. nov., S. gallolyticus subsp. macedonicus subsp. nov., and S. gallolyticus subsp. pasteurianus subsp. nov. within this species. Meanwhile, Poyart et al. (4) demonstrated that a partial sequence of the manganese-dependent superoxide dismutase gene (sodA) provides a useful approach for species differentiation within the so-called S. bovis-Streptococcus equinus group. Consequently, Sasaki et al. (5) has developed a novel PCR-based assay targeting a partial sequence of S. gallolyticus specific sodA for species identification. We therefore performed this PCR assay on type or reference strains of the three subspecies of S. gallolyticus and closely related species, including S. equinus and Streptococcus infantarius. As shown in Table ​Table1,1, the species-specific PCR product was only detected in the three subspecies, supporting the view of Schlegel et al. (6) that these subspecies forms a distinct single taxon at the species level. TABLE 1. Genotypic and metabolic characteristics of strains belonging to three subspecies of S. gallolyticus and its closely related species Most, if not all, of the strains belonging to S. gallolyticus are able to decarboxylate gallate as well as produce tannase, by which a hydrolyzable tannin (i.e., gallotannin) is hydrolyzed to release gallic acid, which is subsequently decarboxylated to pyrogallol (3). Recently, Chamkha et al. (1) demonstrated that S. gallolyticus ACM 3611T also decarboxylated other aromatic compounds, including protocatechuic acid, p-coumaric acid, caffeic acid, and ferulic acid. In this context, we examined the metabolism of these phenolic acids by type strains of the three subspecies of S. gallolyticus, their respective reference strains, and closely related species, including S. equinus and S. infantarius. Tannase and gallate-decarboxylating activities of the strains were determined by the methodology described previously (3). Metabolism of protocatechuic, p-coumaric, caffeic, and ferulic acids by the strains were detected spectrophotometrically, as described by Chamkha et al. (1). Our results showed that all S. gallolyticus strains tested, inclusive of the three subspecies strains, decarboxylated p-coumaric acid and caffeic acid, while the closely related species did not decarboxylate any of the substrates (Table ​(Table1).1). It should also be noted that the strains belonging to S. gallolyticus subsp. macedonicus did not decarboxylate either protocatechuic acid or ferulic acid, which may prove to be useful phenotypic characteristics for identification at the subspecies level.