Additional Bacteriological Examinations Might be Required for the Correct Identification of Staphylococcus warneri.

To the Editor We read with great interest the article, “Native valve endocarditis due to Staphylococcus warneri developing in a patient with type 1 diabetes,” by Yamamoto et al. (1). This article described the patient's clinical course in detail, as well as the clinical decision making that was involved, the deductive interpretation of underlying heart disease, the pathogenicity of coagulase-negative Staphylococci, including Staphylococcus warneri, and diabetes as an accelerating factor. We appreciate the authors' contribution to furthering our understanding of infective endocarditis caused by the extremely rare pathogen S. warneri.

However, an Australian case report described an elderly man suffering from native valve endocarditis caused by S. pasteuri, which has been frequently misidentified as S. warneri because of the strong phenotypic similarity (2). This pathogen was detected by both a biochemical procedure (VITEKⓇ) and matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS). In addition, an article published by a European microbiological laboratory group revealed that four of the nine S. warneri strains were correctly identified based on their phenotype and molecular methods (3). An rRNA restriction fragment length polymorphism analysis (ribotyping) correctly identified all nine S. warneri strains. Furthermore, partial 16S rRNA gene sequencing correctly identified coagulase-negative Staphylococci, which included S. warneri and S. pasteuri (4).

Therefore, we wonder if an additional analysis, such as MALDI-TOF MS, ribotyping or 16S rRNA gene sequencing, was performed for the identification of this rarely isolated microorganism. Although, to our knowledge, no article has yet determined the difference in the clinical course between S. warneri and S. pasteuri, the correct identification of the pathogen is ultimately the most important point when treating infectious diseases.

The authors state that they have no Conflict of Interest (COI).