Abstract
Streptococcus pneumoniae is a major pathogen that causes different invasive pneumococcal diseases (IPD). The pneumococcal polysaccharide capsule is a main virulence factor. More than 94 capsule types have been described, but only a limited number of capsule types accounted for the majority of IPD cases before the introduction of pneumococcal vaccines. After the introduction of the conjugated pneumococcal vaccine PCV7, which covered the seven most frequent serotypes in IPD in the USA, an increase in IPD caused by non-vaccine serotypes was observed, and serotype 19A, which belongs to sequence type (ST) 199, was among the most prevalent STs. After the introduction of the extended vaccine PCV13, which includes serotype 19A, serogroup 15B/C increased in IPD. Therefore, whole genome sequences of 39 isolates of ST199 from Germany (collected between 1998 and 2011) with serotype 19A (n = 24) and serogroup 15B/C (n = 15) were obtained using an Illumina platform and were analysed to identify capsular switches within ST199. Two 19A to 15B/C serotype switch events were identified. Both events occurred before the introduction of PCV7, which indicates that a capsular switch from 19A to 15B among ST199 isolates is not unusual and is not directly linked to the vaccination. The observed serotype replacement appears to be the result of a vacant niche due to the displacement of vaccine serotypes that is now successfully occupied by ST199 clones.
Highlights
Streptococcus pneumoniae are encapsulated, facultative anaerobic, non-sporulating Gram-positive bacteria that usually occur as diplococci
Before 1987, the rate of penicillin nonsusceptible isolates (MIC of ! 0.1 mg/L) associated with Invasive pneumococcal diseases (IPD) has been estimated at 5% in the use in infants between 2000 (USA), but increased to 25.1% in 1999, with PCV7 serotypes accounting for *80% of the cases [51]
These could be reduced to 17% by PCV7 and 14.4% by PCV13 in USA [50]
Summary
Streptococcus pneumoniae are encapsulated, facultative anaerobic, non-sporulating Gram-positive bacteria that usually occur as diplococci. S. pneumoniae, known as pneumococcus, is a major pathogen that causes community-acquired pneumonia (CAP), acute exacerbations of chronic bronchitis, meningitis, sinusitis, otitis media, and sepsis. Pneumococcal infections usually involve infants, immunocompromised individuals and the elderly. Non-invasive diseases (i.e., sinusitis and otitis media) are frequent but not severe. Invasive pneumococcal diseases (IPD) refer to the isolation of S. pneumoniae from a normally sterile site, e.g., blood, cerebrospinal fluid, or pleural fluid, and have a lower incidence but are associated with a high case fatality rate [1]. The main reservoir of S. pneumoniae is the nasopharyngeal zone of healthy carriers, infants. In HIV-endemic regions, the prevalence among the parents might be significantly higher, with rates of 43.2% in HIV-infected parents and 26.8% in HIV-non-infected parents [5]
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