Infective endocarditis caused by Streptococcus tigurinus-like organisms

Abstract

Streptococcus species are important causes of infective endocarditis but species identification remains challenging. We report two cases of infective endocarditis due to Streptococcus tigurinus-like organisms, which were first identified by 16S ribosomal RNA gene sequence analysis and subsequently confirmed using phylogeny based on the analysis of the shetA gene encoding exfoliative toxin.

Keywords: 16S rRNA; PCR; Streptococcus tigurinus; endocarditis; shet A gene.

Fig. 1

Evolutionary relationship of Streptococcus taxa based on the shetA gene. The phylogeny presented is based on the alignment of approximately 640 nucleotides of shetA. The nucleotide sequences were aligned using the multiple alignment options on ClustalW. The phylogenetic tree topology of nucleotide alignment was constructed using the MEGA (Molecular Evolutionary Genetics Analysis) software version 6.06 and the neighbour-joining method. The optimal tree with the sum of branch lengths = 3.15836692 is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) is shown next to the branches. The tree is not rooted and drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Kimura two-parameter method and are represented in the units of the number of base substitutions per site. The analysis included 32 amino acid sequences. All ambiguous positions were removed for each sequence pair. There were a total of 652 positions in the final data set. All sequences are labelled by species, strain name and/or collection and the accession number in brackets. A Staphylococcus aureus shetA sequence was used as the outgroup sequence.