A Case of Recurrent Erysipelas Caused by Streptococcus mitis Group

The c-di-AMP signaling system influences stress tolerance and biofilm formation of Streptococcus mitis

Streptococcus mitis is a commensal bacterial species of the oral cavity, with the potential for opportunistic pathogenesis. For successful colonization, S. mitis must be able to adhere to surfaces of the oral cavity and survive and adapt to frequently changing environmental conditions. Cyclic-di-AMP (c-di-AMP) is a nucleotide second messenger, involved in the regulation of stress responses and biofilm formation in several bacterial species. Cyclic-di-AMP is produced by diadenylate cyclases and degraded by phosphodiesterases. We have previously shown that in S. mitis, one diadenylate cyclase (CdaA) and at least two phosphodiesterases (Pde1 and Pde2) regulate the intracellular concentration of c-di-AMP. In this study, we utilized S. mitis deletion mutants of cdaA, pde1, and pde2 to analyze the role of c-di-AMP signaling in various stress responses, biofilm formation, and adhesion to eukaryotic cells. Here, we demonstrate that the Δpde1 mutant displayed a tendency toward increased susceptibility to acetic acid at pH 4.0. Deletion of cdaA increases auto-aggregation of S. mitis but reduces biofilm formation on an abiotic surface. These phenotypes are more pronounced under acidic extracellular conditions. Inactivation of pde1 or pde2 reduced the tolerance to ciprofloxacin, and UV radiation and the Δpde1 mutant was more susceptible to Triton X-100, indicating a role for c-di-AMP signaling in responses to DNA damage and cell membrane perturbation. Finally, the Δpde2 mutant displayed a tendency toward a reduced ability to adhere to oral keratinocytes. Taken together, our results indicate an important role for c-di-AMP signaling in cellular processes important for colonization of the mouth.

Streptococcus koreensis sp. nov., Isolated from Human Subgingival Dental Plaque of Periodontitis Lesion

A novel facultative anaerobic, Gram-stain-positive coccus, strain JS71^T, was isolated from the human subgingival dental plaque of a periodontitis lesion. Phylogenetic analysis based on the 16S ribosomal RNA gene (16S rDNA) revealed that the strain belonged to the genus Streptococcus. The 16S rDNA sequence had high similarity with Streptococcus rubneri DSM 26920^T (98.6%), Streptococcus parasanguinis ATCC 15912^T (98.5%), and Streptococcus australis CCUG 45919^T (98.3%). The genome of strain JS71^T was 2,009,592 bp in length. The DNA G+C content of the strain was 42.1 mol%. Average nucleotide identity values between strain JS71^T and S. rubneri DSM 26920^T, S. parasanguinis ATCC 15912^T, and S. australis CCUG 45919^T were 88.9%, 80.8%, and 92.4%, respectively. Genome-to-genome distance values between strain JS71^TS. rubneri DSM 26920^T, S. parasanguinis ATCC 15912^T, and S. australis CCUG 45919^T were 36.5% (34-39%), 26.3% (23.9-28.7%), and 48.0% (45.4-50.6%), respectively. The major fatty acids of the strain were C_16:0 (39.7%), C_{18:1 ω6c}/C_{18:1 ω7c} (15.5%), and C_18:0 (10.4%). Based on these results, strain JS71^T (= KCOM 2890^T = JCM 33454^T) should be a novel species of the genus Streptococcus, for which the name Streptococcus koreensis sp. nov. is proposed.