Streptococcus pneumoniae (the pneumococcus) is a Gram-positive bacterium, which
belongs to the species of streptococci. Other pathogenic bacteria belonging to this class
include Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus suis, Streptococcus
uberis, Streptococcus bovis and Streptococcus mutans. In addition, the pneumococcus is
closely related to Lactococcus lactis, a non-pathogenic bacterium used for the production of
dairy products. S. pneumoniae, formerly known as Diplococcus pneumoniae, was described
for the first time in 1881, simultaneously by Louis Pasteur and George Sternberg. Since then,
it has been under extensive study, and this research has significantly contributed to many
fields in biology. The most well known example consists of the pioneering experiments of
Griffith, who showed that non-virulent pneumococcal types could be transformed into
virulent types using heat-killed virulent types (15), suggesting that transfer of hereditary
features had occurred. This seminal observation was the basis that led to the discovery of
DNA as the hereditary material.
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