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22-02-2012 | Cardiology | Article

Newly identified oral bacterium linked to serious disease


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MedWire News: A newly discovered bacterium that lives in the mouth has been linked to serious infectious diseases affecting the heart and brain, research shows.

The team that led the research calls for urgent work to characterize the bacterium, named Streptococcus tigurinus, and to understand the risk it poses to carriers.

The bacterium was identified by Andrea Zbinden's team at the Institute of Medical Microbiology, University of Zurich, Switzerland. It was first isolated from a 74-year-old patient with endocarditis and, on molecular sequencing, found to belong to the Streptococcus mitis group.

S. mitis is known to colonize the mouth, note Zbinden et al, and is recognized as an important causative agent in endocarditis.

Further analysis showed that the novel bacterium was anerobic, Gram-positive, catalase-negative, and coccus-shaped, and shared 98.6% sequence similarity with S. mitis strain type ATCC 49456T.

The researchers searched their molecular database, which revealed three further streptococcal isolates that matched the novel bacterium. These samples had come from oral samples taken from patients with endocarditis, meningitis, and spondylodiscitis.

Further evaluation confirmed that all four isolates were a novel species of the S. mitis group. They were named S. tigurinus sp. nov., after the region of Zurich in which they were first recognized.

Commenting on their discovery, Zbinden et al say that S. tigurinus may have remained undetected because of its close similarity to other S. mitis strains. They warn that it seems to have "a natural potential to cause severe disease," making it important for clinicians and microbiologists to be aware of it.

"Further research must now be done to understand the strategies S. tigurinus uses to successfully cause disease," said Zbinden in a press statement accompanying the study.

She continued: "The next step is to work out exactly how common this bacterium is in the oral cavity and what risk it poses. Immunosuppression, abnormal heart valves, dental surgeries or chronic diseases are common predisposing factors for blood infections by this group of bacteria. However, the specific risk factors for S. tigurinus remain to be determined."

The research is published in the International Journal of Systematic and Evolutionary Microbiology.

By Joanna Lyford

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