关于 Streptococcus pneumoniae

Streptococcus pneumoniae (S. pneumoniae) is a gram-positive bacterium with a round or oval body, usually arranged in pairs or short chains^[1]. It has no flagella, does not form spores, and belongs to the family Streptococcaceae. S. pneumoniae is a common respiratory pathogen that predominantly lives in the nasopharynx of the human body^[2] with a bacterial carrier rate of less than 10% in healthy adults  and between 27% and 65% in children^[3] and it can be transmitted by droplets, invade the respiratory tract and cause infection^[4]. When the body's immunity is weakened or the respiratory tract is damaged, S. pneumoniae can easily take advantage of the weakness and cause serious diseases such as pneumonia, otitis media, meningitis, non-invasive and invasive pneumococcal diseases (IPD)^[5]. S. pneumoniae infection typically causes symptoms such as high fever, chills, cough, and chest pain^[6]. If left untreated, the infection can spread further, leading to more serious complications and even life-threatening^[7].

S. pneumoniae express a variety of virulence factors such as the pore-forming toxin, pneumolysin, adhesin (pneumococcal adhesion and virulence protein A [PavA] and pneumococcal adhesion and virulence protein B [PavB]), fimbria, pyruvate oxidase, IgA1 protease, and exoglycosidases to promote their survival in the host^[7]. These virulence factors act by hindering the host's immune system response, avoiding defense mechanisms, or by direct contact with host tissues and surface receptors, which in turn interferes with the host's immune system activation and bacterial clearance^[8].

Thus far, over100 pneumococcal capsular serotypes have been identified^[9]. Distinct capsular serotypes may differ in their ability to colonize the nasopharynx or cause IPD. Serotype 1 was among the first serotypes discovered in the early 20th century^[10] and ranks among the most common serotypes associated with IPD globally, particularly in Sub-Saharan Africa, South America and Asia, where it is widely associated with outbreaks. Clinical isolates producing serotype 3 capsule have a highly mucoid appearance and a wet phenotype when grown on plates. In contrast, other serotypes form more discrete colonies. Serotype 3 have historically been associated with a much higher attack rate and/or morbidity than other serotypes and often has severe clinical manifestations: most commonly bacteremia-induced septic shock, meningitis, and pneumonia^[11].

The introduction of pneumococcal vaccines, which target common invasive serotypes, the epidemiology and distribution of S. pneumoniae serotypes have undergone large changes over the last two decades^[12]. The first pneumococcal vaccine was the 7-valent pneumococcal conjugate vaccine (7vPCV) in 2005 and targeted serotypes 4, 6B, 9V, 14, 18C, 19F and 23F. In 2011, the 7vPCV was changed to a 13 valent vaccine (13vPCV) which, in addition to the serotypes included in the 7vPCV, targeted 1, 3, 5, 6A, 7F and 19A. In addition, there is a 23-valent pneumococcal polysaccharide vaccine (23vPPV) that is recommend for those with medical risk factors and the elderly. The 23vPPV includes all serotypes included in the 13vPCV as well as serotype 2, 8, 9N, 10A, 11A, 12F, 15B, 17F, 20B, 22F and 33F.

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