Abstract
BackgroundAlthough serogroup 20 is not part of any conjugate pneumococcal vaccine, its serotype 20A, but not 20B, belongs to the polysaccharide 23-valent formula. Little is known about its clinical, laboratorial and epidemiological characteristics.MethodsThe purpose of this study was to evaluate the bacterial genotypes (by PFGE and MLST), clinical characteristics of patients (from review of medical records) and antimicrobial susceptibility of serogroup 20 isolates which were recovered from patients with invasive pneumococcal disease (IPD) from 2007 to 2012. Subtyping to determine 20A and 20B types was also performed by sequencing the genes of the cps locus.ResultsSixteen isolates were genotyped and were highly related. All pneumococci were resistant to tetracycline and 31 % were non-susceptible to trimethoprim/sulfamethoxazole. Penicillin MIC ranged from 0.004 to 1 μg/mL and non-susceptibility (MIC ≥ 0.12 μg/mL) was observed in 5/16 isolates (31 %). All isolates belonged to subtype 20B. Most patients were male with a median age of 62 years and presented at least one underlying disease (mostly respiratory conditions). All isolates belonged to ST8889 and to a unique PFGE clone.ConclusionsA high clonal occurrence of serotype 20B pneumococci recovered from patients with IPD in Brazil was observed. As a non-PCV10 serotype, selective pressure may be responsible for this unusual occurrence of serogroup 20. However, temporal variation effect should not be underestimated; therefore it is an issue that warrants continued monitoring.
Highlights
Serogroup 20 is not part of any conjugate pneumococcal vaccine, its serotype 20A, but not 20B, belongs to the polysaccharide 23-valent formula
Yildirim and co-workers (2012) [17] evaluated prevalence of serotypes causing invasive diseases in two periods: directly after PCV7 implementation in USA (2000-2002) and a few years later (2009-10) and observed an increase in the proportion of invasive disease caused by serogroup 20
It is well known that temporal variations in the distribution of pneumococcal serotypes are expected, independent of selective pressure due to antibiotic use or vaccination and is a more likely explanation for the changes in prevalence seen in this study than is vaccine-related serotype replacement [32]
Summary
Serogroup 20 is not part of any conjugate pneumococcal vaccine, its serotype 20A, but not 20B, belongs to the polysaccharide 23-valent formula. In Brazil, serogroup 20 has recently been recognized among the more prevalent serotypes in the post-vaccine period [23]. Analysis of these isolates by multilocus sequence typing (MLST) identified them as belonging to the same (and newly described) sequence type (ST) 8889. Caierão et al BMC Infectious Diseases (2016) 16:418 belonging to serogroup 20 based on differences in the cps locus and designated these variants as 20A and 20B. They showed distinguishable antigenicity when human sera from patients who were vaccinated with the PPV23 were used. The authors concluded that this vaccine contains serotype 20A polysaccharide, but not 20B
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