In international case studies, pneumococcus is portrayed as the etiopathological factor most involved in the onset of pneumonia.

The current scientific name of pneumococcus is Streptococcus pneumoniae, while in the past it was better known as Diplococcus pneumoniae, with reference to the peculiar morphology of the bacterium: in fact, observed under an optical microscope, the pneumococcus appears as two joined cocci, apparently fused at one "end, which gives the characteristic" flame "shape.

In this introductory article, attention is paid to the general and microbiological description of the pneumococcus, and to the epidemiology of the infection.

Microbiological analysis

In addition to being the protagonist par excellence of pneumonia, pneumococcus - which entered the body by inhalation of micro-droplets of infected saliva - is also involved in other highly invasive pathologies and in further minor disturbances. Nisseria meningitidis (meningococcus), is for example involved in the manifestation of bacterial meningitis, a potentially fatal disease consisting of an acute, sudden and violent inflammatory process of the meninges.

  1. More ferocious diseases mediated by pneumococcus → septic arthritis, brain abscess, bacteremia, infectious cellulitis (not to be confused with aesthetic cellulitis), meningitis, osteomyelitis, pericarditis and peritonitis.
  2. Minor diseases developed by pneumococcus → bronchitis, conjunctivitis, otitis media and sinusitis.

The Streptococcus pneumoniae it is a gram positive bacterium of the alpha haemolytic type in aerobiotic state and of the beta-haemolytic type in anaerobic conditions. Belonging to the genus Streptococcus, pneumococcus has a circular genome, containing 2.0-2.1 million base pairs; in the nucleus there are 1553 genes, of which 154 contribute to virulence and 176 retain an invasive phenotype.
Some pneumococcal strains, especially those with capsulapolisaccharide, are particularly virulent; it is precisely the capsular polysaccharide that confers virulence to the pathogen, since this external coating protects the microorganism from phagocytosis and, at the same time, increases its pathogenicity.
The cell wall of the pneumococcus consists largely of the M protein and the C antigen, which in turn is composed of theic acid, choline and galactosamine-6-phosphate.
Pneumococcus undergoes autolysis phenomena, after which it tends to originate non-capsulated bacterial colonies, far less virulent than the previous (capsulated) forms.
Pneumococcus is a fermenting bacterium, capable of forming lactic acid starting from glucose: this ability heavily affects the choice of the culture medium, which must be composed of a quantity derisory glucose; in fact the pneumococcus, cultivated on blood agar medium enriched with glucose, would quickly transform this sugar into lactic acid, which would lead to a lowering of the pH, consequently the growth of the microorganism would be compromised by the excessive acidity of the medium. The ideal culture medium for pneumococcus is blood agar embellished with beef heart or soy protein, clearly low in glucose.
Even if the pneumococcus is a commensal microorganism, normally present in the mucous membranes of the respiratory tract, in optimal conditions it can replicate indiscriminately, transforming itself into an opportunistic pathogen.
To date, there are over 90 serotypes of Pneumococcus, most of which are capable of triggering infections, especially affecting the respiratory system and the nervous system. Among these, serotypes 1, 3, 4, 5, 7, 8, 12, 14 and 19 are those that share the majority of pneumococcal infections.

Incidence of infections

Infections caused by pneumococcus are a serious public health problem everywhere, even if the damage that the bacterium can develop is heavily influenced by the hygienic conditions of the country; just think of the danger that a "pneumococcal infection can create in developing nations. The pathogen preferentially (though not exclusively) affects children under the age of 5 (especially from 6 months of age), causing annually approximately one million deaths: pneumococcal deaths are observed above all in those countries where health resources (drugs and hospitals) are scarce, and personal and environmental hygiene leave something to be desired.
Children are the bacterium's favorite targets, probably because they are not yet able to develop antibodies to pneumococcal polysaccharide antigens; to this first factor is also added the high frequency of bacterial colonization in the child, which could explain both the susceptibility to pneumococcal attack and the poor efficacy of unconjugated polysaccharide vaccines.
In general, pneumococcus constitutes the etiological element most involved in pneumonia, otitis media and occult bacteremia; in Italy, the frequency of pneumococcal infections is comparable to that of meningococcus.


Data in hand, it was observed that infections major pneumococcal mediated are supported by some specific serum groups: this means that not all pneumococci tend to develop severe damage. Considering infected patients of any age, it is estimated that 80% of pneumococcal infections are caused by one or more pneumococci belonging to 12 serum groups; children under the age of 6, instead, they are more affected by 6 serum groups.
In general terms, pneumococcus is estimated to affect 5.2-15.2 inhabitants per 100,000.
The number of patients treated for pneumococcal infections increases if the target is narrowed: in children aged 0 to 5 years, pneumococcal infections are believed to occur in 10.1-24.2 cases per 100,000 children.

Risk factors

RISK FACTORS: it has been observed that pneumococcal infections are more frequent among males, especially of black ethnicity; for example, American blacks, Australian aborigines, and American Indians tend to be affected 2 to 10 times more than healthy white children.
Among the other most common risk factors, able to favor pneumococcal infections, we cannot forget cigarette smoking, bronchial asthma and flu diseases. Still, other pathologies can predispose the patient to pneumococcal insults: congenital immunodeficiencies or acquired (AIDS), complement factor deficiencies, Diabetes Mellitus, congestive heart failure, chronic lung disease, nephrotic syndrome and thalassemia major.
The intake of drugs and narcotic substances can also reduce the phagocytic activity of macrophages (defense function), as well as the cough reflex, which can favor the inhalation of pneumococci.

Other articles on "Pneumococcus"

  1. Pneumococcus - infection, symptoms, diagnosis, therapy
  2. Pneumococcal Vaccination - Anti-Pneumococcal Vaccine
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