Gene regulation in Streptococcus pneumoniae - RePub - Erasmus ...

Chapter 1
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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 (2).
Pneumococcal colonization and disease
Usually pneumococcus resides in the nasopharynx as a harmless commensal (Fig. 1).
However, in children below the age of two years, immune-compromised persons, and elderly
above the age of 65, the bacterium can cause serious infections such as otitis media,
bacteremic pneumonia, meningitis, or bacteremia (Fig. 1). It is estimated that over 1 million
children die from pneumococcal disease every year (6), most of them living in developing
countries. In these countries medical aid is often only scarcely available, and the same is true
for access to vaccines.
Invasive disease caused by pneumococci is always preceded by colonization in which
the bacteria attach to the epithelial layer in the nasopharynx (Fig. 1). In susceptible
individuals, colonization can lead to bacterial spread from the nasopharynx to the Eustachian
tube, the lower respiratory tract, and the blood, causing serious infections (Fig. 1). A thorough
understanding of the pneumococcal components required for pathogenicity and virulence is
essential to combat disease. These components are often referred to as virulence factors,
although many of these might contribute to virulence only indirectly, by affecting the overall
fitness of the bacterium.