A Streptococcus pneumoniae lineage usually associated with pneumococcal conjugate vaccine (PCV) serotypes is the most common cause of serotype 35B invasive disease in South Africa, following routine use of PCV

Update on the evolving landscape of pneumococcal capsule types: new discoveries and way forward

SUMMARYStreptococcus pneumoniae (the "pneumococcus") is a significant human pathogen. The key determinant of pneumococcal fitness and virulence is its ability to produce a protective polysaccharide (PS) capsule, and anti-capsule antibodies mediate serotype-specific opsonophagocytic killing of bacteria. Notably, immunization with pneumococcal conjugate vaccines (PCVs) has effectively reduced the burden of disease caused by serotypes included in vaccines but has also spurred a relative upsurge in the prevalence of non-vaccine serotypes. Recent advancements in serotyping and bioinformatics surveillance tools coupled with high-resolution analytical techniques have enabled the discovery of numerous new capsule types, thereby providing a fresh perspective on the dynamic pneumococcal landscape. This review offers insights into the current pneumococcal seroepidemiology highlighting important serotype shifts in different global regions in the PCV era. It also comprehensively summarizes newly discovered serotypes from 2007 to 2024, alongside updates on revised chemical structures and the de-novo determinations of structures for previously known serotypes. Furthermore, we spotlight emerging evidence on non-pneumococcal Mitis-group strains that express capsular PS that are serologically and biochemically related to the pneumococcal capsule types. We further discuss the implications of these recent findings on capsule nomenclature, pneumococcal carriage detection, and future PCV design. The review maps out the current status and also outlines the course for future research and vaccine strategies, ensuring a continued effective response to the evolving pneumococcal challenge.

Genomic characterization of Streptococcus pneumoniae isolates obtained from carriage and disease among paediatric patients in Addis Ababa, Ethiopia

Background and aims. Despite the introduction of pneumococcal conjugate vaccines (PCVs), Streptococcus pneumoniae still remains an important cause of morbidity and mortality, especially among children under 5 years in sub-Saharan Africa. We sought to determine the distribution of serotypes, lineages and antimicrobial resistance of S. pneumoniae from carriage and disease among children presenting to health facilities, 5-6 years after the introduction of PCV10 in Ethiopia.Methods. Whole-genome sequencing (WGS) was performed on 103 S. pneumoniae (86 from nasopharyngeal swabs, 4 from blood and 13 from middle ear discharge) isolated from children aged <15 years at 3 healthcare facilities in Addis Ababa, Ethiopia, from September 2016 to August 2017. Using the WGS data, serotypes were predicted, isolates were assigned to clonal complexes, global pneumococcal sequence clusters (GPSCs) were inferred and screening for alleles and mutations that confer resistance to antibiotics was performed using multiple bioinformatic pipelines.Results. The 103 S. pneumoniae isolates were assigned to 38 serotypes (including nontypeable) and 46 different GPSCs. The most common serotype was serotype 19A. Common GPSCs were GPSC1 [14.6% (15/103), sequence type (ST) 320, serotype 19A], GPSC268 [8.7% (9/103), ST 6882 and novel STs; serotypes 16F, 11A and 35A] and GPSC10 [8.7% (9/103), STs 2013, 230 and 8804; serotype 19A]. The four invasive isolates were serotype 19A (n=2) and serotype 33C (n=2). Resistance to penicillin (>0.06 µg ml-1, CLSI meningitis cutoff) was predicted in 57% (59/103) of the isolates, and 43% (25/58) penicillin-binding protein allele combinations were predicted to be associated with penicillin resistance. Resistance mutations in folA (I100L) and/or folP (indel between fifty-sixth and sixty-seventh aa) were identified among 66% (68/103) of the isolates, whilst tetracycline (tetM) and macrolide (ermB and mefA) resistance genes were found in 46.6% (48/103), 20.4% (21/103) and 20.4% (21/103) of the isolates, respectively. Multidrug resistance (MDR) (≥3 antibiotic classes) was observed in 31.1% (32/103) of the isolates. GPSC1 and GPSC10 accounted for 46.8% (15/32) and 18.7% (6/32) of the overall MDR.Conclusion. Five to 6 years after the introduction of PCV10 in Ethiopia, the S. pneumoniae obtained from carriage and disease among paediatric patients showed diverse serotype and pneumococcal lineages. The most common serotype identified was 19A, expressed by the MDR lineages GPSC1 and GPSC10, which is not covered by PCV10 but is included in PCV13. Continued assessment of the impact of PCV on the population structure of S. pneumoniae in Ethiopia is warranted during and after PCV13 introduction.

Investigating two decades of Streptococcus pneumoniae bacteraemia in the Gelderland area, the Netherlands, using whole-genome sequencing

In the Netherlands, the 7-valent pneumococcal conjugate vaccine (PCV) was introduced to the childhood immunization programme in 2006 and replaced by the 10-valent PCV (PCV10, GSK) in 2011. To describe invasive pneumococcal disease in the era of childhood PCV vaccination on pneumococcal bacteraemia across all ages, we collected and sequenced 979 pneumococcal blood isolates from consecutive patients with pneumococcal bacteraemia in the Gelderland area, the Netherlands, between 2000 and 2020. In total, 58% of the bacteraemia cases (n=563/979) occurred in the elderly population. Compared to the pre-PCV period (2000-2005), the odds ratio for non-PCV10 bacteraemia was 17.5 (CI 9.9-31.6; P<0.001) in the late-PCV10 period, showing an overall increase in the proportion of bacteraemia cases being caused by non-vaccine serotype pneumococci (2016-2020). The increase in non-PCV10 serotypes is mainly driven by an expansion of lineage global pneumococcal sequencing cluster 3 (GPSC3) expressing serotype 8, alongside the emergence of serotype 12F that was mediated by multiple lineages (GPSC32/GPSC26/GPSC55). Both serotypes 8 and 12F were included in the latest PCV20 formulation that is licensed to be used in children and adults in Europe. Over 20 years, we observed a low prevalence of antimicrobial resistance (AMR) as predicted by genome data. There were no significant changes in AMR prevalence after vaccine introduction (P>0.05 for all comparisons). We saw a stably low prevalence of reduced penicillin susceptibility, which was observed in multiple pneumococcal lineages, with GPSC10 being the most common in the Gelderland collection, whilst GPSC1 and GPSC6 were common among the penicillin-resistant pneumococcal blood culture isolates provided by the Netherlands Reference Laboratory for Bacterial Meningitis. Comparison to global collections of GPSC10, GPSC1 and GPSC6 isolates favored the likelihood of separate introductions of penicillin-resistant isolates rather than cloncal expansion. Genomic surveillance of pneumococcal bacteraemia in this unbiased population sample in the Netherlands supports the use of higher valency PCVs, such as PCV20, especially in adults, to prevent future bacteraemia cases caused by Streptococcus pneumoniae in the Gelderland area, the Netherlands, while maintaining a low prevalence of AMR in the pneumococcal population.

Geographical migration and fitness dynamics of Streptococcus pneumoniae

Streptococcus pneumoniae is a leading cause of pneumonia and meningitis worldwide. Many different serotypes co-circulate endemically in any one location1,2. The extent and mechanisms of spread and vaccine-driven changes in fitness and antimicrobial resistance remain largely unquantified. Here using geolocated genome sequences from South Africa (n = 6,910, collected from 2000 to 2014), we developed models to reconstruct spread, pairing detailed human mobility data and genomic data. Separately, we estimated the population-level changes in fitness of strains that are included (vaccine type (VT)) and not included (non-vaccine type (NVT)) in pneumococcal conjugate vaccines, first implemented in South Africa in 2009. Differences in strain fitness between those that are and are not resistant to penicillin were also evaluated. We found that pneumococci only become homogenously mixed across South Africa after 50 years of transmission, with the slow spread driven by the focal nature of human mobility. Furthermore, in the years following vaccine implementation, the relative fitness of NVT compared with VT strains increased (relative risk of 1.68; 95% confidence interval of 1.59-1.77), with an increasing proportion of these NVT strains becoming resistant to penicillin. Our findings point to highly entrenched, slow transmission and indicate that initial vaccine-linked decreases in antimicrobial resistance may be transient.

Pneumococcal population genomics changes during the early time period of conjugate vaccine uptake in southern India

Streptococcus pneumoniae is a major cause of invasive disease of young children in low- and middle-income countries. In southern India, pneumococcal conjugate vaccines (PCVs) that can prevent invasive pneumococcal disease began to be used more frequently after 2015. To characterize pneumococcal evolution during the early time period of PCV uptake in southern India, genomes were sequenced and selected characteristics were determined for 402 invasive isolates collected from children <5 years of age during routine surveillance from 1991 to 2020. Overall, the prevalence and diversity of vaccine type (VT) and non-vaccine type (NVT) isolates did not significantly change post-uptake of PCV. Individually, serotype 1 and global pneumococcal sequence cluster (GPSC or strain lineage) 2 significantly decreased, whereas serotypes 6B, 9V and 19A and GPSCs 1, 6, 10 and 23 significantly increased in proportion post-uptake of PCV. Resistance determinants to penicillin, erythromycin, co-trimoxazole, fluoroquinolones and tetracycline, and multidrug resistance significantly increased in proportion post-uptake of PCV and especially among VT isolates. Co-trimoxazole resistance determinants were common pre- and post-uptake of PCV (85 and 93 %, respectively) and experienced the highest rates of recombination in the genome. Accessory gene frequencies were seen to be changing by small amounts across the frequency spectrum specifically among VT isolates, with the largest changes linked to antimicrobial resistance determinants. In summary, these results indicate that as of 2020 this pneumococcal population was not yet approaching a PCV-induced equilibrium and they highlight changes related to antimicrobial resistance. Augmenting PCV coverage and prudent use of antimicrobials are needed to counter invasive pneumococcal disease in this region.

Establishing a national reference laboratory for antimicrobial resistance using a whole-genome sequencing framework: Nigeria's experience

Whole-genome sequencing (WGS) is finding important applications in the surveillance of antimicrobial resistance (AMR), providing the most granular data and broadening the scope of niches and locations that can be surveilled. A common but often overlooked application of WGS is to replace or augment reference laboratory services for AMR surveillance. WGS has supplanted traditional strain subtyping in many comprehensive reference laboratories and is now the gold standard for rapidly ruling isolates into or out of suspected outbreak clusters. These and other properties give WGS the potential to serve in AMR reference functioning where a reference laboratory did not hitherto exist. In this perspective, we describe how we have employed a WGS approach, and an academic-public health system collaboration, to provide AMR reference laboratory services in Nigeria, as a model for leapfrogging to national AMR surveillance.