STREPTOCOCCUS PNEUMONIAE, or PNEUMOCOCCUS, is a
alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under
anaerobic conditions) , facultative anaerobic member of the genus
Streptococcus . As a significant human pathogenic bacterium S.
pneumoniae was recognized as a major cause of pneumonia in the late
19th century, and is the subject of many humoral immunity studies.
S. pneumoniae resides asymptomatically in healthy carriers typically
colonizing the respiratory tract, sinuses, and nasal cavity . However,
in susceptible individuals with weaker immune systems , such as the
elderly and young children, the bacterium may become pathogenic and
spread to other locations to cause disease. It can be a cause of
neonatal infections .
S. pneumoniae is the main cause of community acquired pneumonia and
meningitis in children and the elderly, and of septicemia in those
HIV . The organism also causes many types of
pneumococcal infections other than pneumonia . These invasive
pneumococcal diseases include bronchitis , rhinitis , acute sinusitis
, otitis media , conjunctivitis , meningitis , sepsis , osteomyelitis
, septic arthritis , endocarditis , peritonitis , pericarditis ,
cellulitis , and brain abscess .
S. pneumoniae can be differentiated from the viridans streptococci ,
some of which are also alpha-hemolytic , using an optochin test, as S.
pneumoniae is optochin-sensitive. S. pneumoniae can also be
distinguished based on its sensitivity to lysis by bile , the
so-called "bile solubility test". The encapsulated , Gram-positive
coccoid bacteria have a distinctive morphology on Gram stain, lancet
-shaped diplococci. They have a polysaccharide capsule that acts as a
virulence factor for the organism; more than 90 different serotypes
are known, and these types differ in virulence , prevalence , and
extent of drug resistance .
* 1 History
* 2 Genetics
* 2.1 Transformation
* 5 Interaction with
* 6 Diagnosis
* 7 See also
* 8 References
* 9 External links
In 1881, the organism, known later in 1886 as the pneumococcus for
its role as a cause of pneumonia, was first isolated simultaneously
and independently by the U.S. Army physician George Sternberg and
the French chemist
Louis Pasteur .
The organism was termed Diplococcus pneumoniae from 1920 because of
its characteristic appearance in Gram-stained sputum . It was renamed
Streptococcus pneumoniae in 1974 because it was very similar to
S. pneumoniae played a central role in demonstrating that genetic
material consists of
DNA . In 1928
Frederick Griffith demonstrated
transformation of life turning harmless pneumococcus into a lethal
form by co-inoculating the live pneumococci into a mouse along with
heat-killed virulent pneumococci. In 1944
Oswald Avery , Colin
MacLeod , and
Maclyn McCarty demonstrated the transforming factor in
Griffith\'s experiment was not protein , as was widely believed at the
time, but DNA. Avery's work marked the birth of the molecular era of
The genome of S. pneumoniae is a closed, circular
DNA structure that
contains between 2.0 and 2.1 million base pairs depending on the
strain . It has a core set of 1553 genes , plus 154 genes in its
virulome, which contribute to virulence and 176 genes that maintain a
noninvasive phenotype . Genetic information can vary up to 10% between
Natural bacterial transformation involves the transfer of
one bacterium to another through the surrounding medium.
Transformation is a complex developmental process requiring energy and
is dependent on expression of numerous genes. In S. pneumoniae at
least 23 genes are required for transformation. In order for a
bacterium to bind, take up and recombine exogenous
DNA into its
chromosome it must enter a special physiological state called
Competence in S. pneumoniae is induced by DNA-damaging agents such as
mitomycin C , fluoroquinolone antibiotics (norfloxacin , levofloxacin
and moxifloxacin ), and topoisomerase inhibitors . Transformation
protects S. pneumoniae against the bactericidal effect of mitomycin C.
Michod et al. summarized evidence that induction of competence in S.
pneumoniae is associated with increased resistance to oxidative stress
and increased expression of the RecA protein, a key component of the
recombinational repair machinery for removing
DNA damages . On the
basis of these findings they suggested that transformation is an
adaptation for repairing oxidative
DNA damages. S. pneumoniae
infection stimulates polymorphonuclear leukocytes (granulocytes) to
produce an oxidative burst that is potentially lethal to the bacteria.
The ability of S. pneumoniae to repair the oxidative
DNA damages in
its genome, caused by this host defense, likely contributes to this
pathogen’s virulence. Consistent with this premise Li et al.
reported that, among different highly transformable S. pneumoniae
isolates, nasal colonization fitness and virulence (lung infectivity)
depend on an intact competence system.
S. pneumoniae is part of the normal upper respiratory tract flora .
As with many natural flora it can become pathogenic under the right
conditions, typically when the immune system of the host is suppressed
Invasins , such as pneumolysin , an anti-phagocytic capsule ,
various adhesins , and immunogenic cell wall components are all major
virulence factors . Once it colonizes the alveoli the body responds by
stimulating the inflammatory response causing plasma, blood, and white
blood cells to fill the alveoli. This condition is called pneumonia.
It is susceptible to clindamycin .
Due to the importance of disease caused by S. pneumoniae several
vaccines have been developed to protect against invasive infection.
World Health Organization
World Health Organization recommend routine childhood pneumococcal
vaccination; it is incorporated into the childhood immunization
schedule in a number of countries including the United Kingdom,
United States, and South Africa.
INTERACTION WITH HAEMOPHILUS INFLUENZAE
Haemophilus influenzae (H. influenzae) has been a
significant cause of infection and both H. influenzae and S.
pneumoniae can be found in the human upper respiratory system . A
study of competition in vitro revealed S. pneumoniae overpowered H.
influenzae by attacking it with hydrogen peroxide . However, in a
study adding both bacteria to the nasal cavity of a mouse within 2
weeks only H. influenzae survives; further analysis showed that
neutrophils exposed to dead H. influenzae were more aggressive in
attacking S. pneumoniae.
Diagnosis is generally made based on clinical suspicion along with a
positive culture from a sample from virtually any place in the body.
An ASO Titre of >200 units is significant. S. pneumoniae is, in
general, optochin sensitive, although optochin resistance has been
Atromentin and leucomelone possess antibacterial activity, inhibiting
the enzyme enoyl-acyl carrier protein reductase , (essential for the
biosynthesis of fatty acids ) in S. pneumoniae.
in a culture of
Pneumococcal Awareness Council of Experts
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