Description of Streptococcus thalassemiae sp. nov., a Bacterium Isolated from Human Blood

Blood is a precious biological liquid that is normally sterile. Therefore, bacteria in the bloodstream are shown a priori anomaly. A blood culture is systematically performed to diagnose the cause of the bacteremia. Indeed, a patient received in our service had a thalassemia major and underwent a genoidentical transplant. Then, a blood test was performed to diagnose a four-day fever. In this context, we have isolated strain Marseille-Q2617 from the blood sample. It revealed a new bacterial strain that belongs to the genus Streptococcus. It is a Gram-positive coccus, nonmotile, and nonspore forming. The major fatty acid found is hexadecanoic acid, with 49.5%. A taxonomic method was used to characterize the strain by studying their phenotypic, phylogenetic, and genomic characteristics. In addition, sequence analysis of the 16S rRNA gene shows that the strain Marseille-Q2617 has 99.94% sequence similarity to Streptococcus mitis. Average nucleotide identity (ANI) analysis for strain Marseille-Q2617(T) showed the highest similarity of 92.9% with S. mitis. The DNA-DNA hybridization value obtained (50.2%) between strain Marseille-Q2607 and S. mitis, its closest related species, was below the recommended threshold (<70%). Strain Marseille-Q2617(T) has a genome size of 2.02 Mbp with 40.5 mol% of G + C content. Based on these results, we propose a new species of the genus Streptococcus, for which the name Streptococcus thalassemiae sp. nov., Marseille-Q2617(T) (=CSUR Q2617 = CECT 30109) was proposed.

Automated summary

Blood is normally sterile, but bacteria in the bloodstream indicate an anomaly. By performing a blood culture on a patient with thalassemia major, a new strain of Streptococcus was isolated and identified through phenotypic, phylogenetic, and genomic characteristics analysis. Named Streptococcus thalassemiae sp. nov., this strain showed similarity to Streptococcus mitis but had significant differences based on DNA-DNA hybridization and average nucleotide identity analysis. This research demonstrates the importance of studying bacterial strains in blood cultures for accurate diagnosis.