Why pneumococci affect primarily humans

Published 2016-09-02 10:35. Updated 2016-09-02 10:48

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A special variant of a sugar molecule in the human nose might explain why pneumococcal infections are more common in humans than in other animals, researchers from Karolinska Institutet report in a study published in the journal Cell Host & Microbe. The discovery can help in the search for a broader vaccine able to protect against all types of pneumococci.

The bacterium S. pneumoniae or the pneumococcus exists naturally in the noses of children and adults, but is also one of the most common causes of infectious diseases in the world, with meningitis and pneumonia being amongst the most severe. Pneumococci cause more severe infections in humans than in other mammals, something that has hitherto remained a mystery.

Nasal mucus contains a special sugar molecule – sialic acid – which pneumococci use as a source of energy for its growth and survival. With the help of an enzyme this acid is released by the bacteria and taken up into the bacterial cells for conversion to energy. In this present study, the researchers show that the sialic acid found in humans make pneumococci able to both grow better and become more resistant to the immune defence than the variant commonly found in other mammals.

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