Identification and genetic engineering of pneumococcal capsule-like polysaccharides in commensal oral streptococci

Capsular polysaccharides (CPS) in Streptococcus pneumoniae are pivotal for bacterial virulence and present extensive diversity. While oral streptococci show pronounced antigenicity toward pneumococcal capsule-specific sera, insights into evolution of capsule diversity remain limited. This study reports a pneumococcal CPS-like genetic locus in Streptococcus parasanguinis, a predominant oral Streptococcus. The discovered locus comprises 15 genes, mirroring high similarity to those from the Wzy-dependent CPS locus of S. pneumoniae. Notably, S. parasanguinis elicited a reaction with pneumococcal 19B antiserum. Through nuclear magnetic resonance analysis, we ascertained that its CPS structure matches the chemical composition of the pneumococcal 19B capsule. By introducing the glucosyltransferase gene cps19cS from a pneumococcal serotype 19C, we successfully transformed S. parasanguinis antigenicity from 19B to 19C. Furthermore, substituting serotype-specific genes, cpsI and cpsJ, with their counterparts from pneumococcal serotype 19A and 19F enabled S. parasanguinis to generate 19A- and 19F-specific CPS, respectively. These findings underscore that S. parasanguinis harbors a versatile 19B-like CPS adaptable to other serotypes. Remarkably, after deleting the locus's initial gene, cpsE, responsible for sugar transfer, we noted halted CPS production, elongated bacterial chains, and diminished biofilm formation. A similar phenotype emerged with the removal of the distinct gene cpsZ, which encodes a putative autolysin. These data highlight the importance of S. parasanguinis CPS for biofilm formation and propose a potential shared ancestry of its CPS locus with S. pneumoniae.

IMPORTANCE

Diverse capsules from Streptococcus pneumoniae are vital for bacterial virulence and pathogenesis. Oral streptococci show strong responses to a wide range of pneumococcal capsule-specific sera. Yet, the evolution of this capsule diversity in relation to microbe-host interactions remains underexplored. Our research delves into the connection between commensal oral streptococcal and pneumococcal capsules, highlighting the potential for gene transfer and evolution of various capsule types. Understanding the genetic and evolutionary factors that drive capsule diversity in S. pneumoniae and its related oral species is essential for the development of effective pneumococcal vaccines. The present findings provide fresh perspectives on the cross-reactivity between commensal streptococci and S. pneumoniae, its influence on bacteria-host interactions, and the development of new strategies to manage and prevent pneumococcal illnesses by targeting and modulating commensal streptococci.

Correlates of Nonrandom Patterns of Serotype Switching in Pneumococcus

BACKGROUND

Pneumococcus is a diverse pathogen, with >90 serotypes, each of which has a distinct polysaccharide capsule. Pneumococci can switch capsules, evading vaccine pressure. Certain serotype pairs are more likely to occur on the same genetic background as a results of serotype switching, but the drivers of these patterns are not well understood.

METHODS

We used the PubMLST and Global Pneumococcal Sequencing Project databases to quantify the number of genetic lineages on which different serotype pairs occur together. We also quantified the genetic diversity of each serotype. Regression model were used to evaluate the relationship between shared polysaccharide components and the frequency of serotype co-occurrence and diversity.

RESULTS

A number of serotype pairs occurred together on the same genetic lineage more commonly than expected. Co-occurrence of between-serogroup pairs was more common when both serotypes had glucose as a component of the capsule (and, potentially, glucuronic acid, any-N-acetylated sugar, or ribitol). Diversity also varied markedly by serotype and was associated with the presence of specific sugars in the capsule.

CONCLUSIONS

Certain pairs of serotypes are more likely to co-occur on the same genetic background. These patterns were correlated with shared polysaccharide components. This might reflect adaptation of strains to produce capsules with specific characteristics.

Serotype Distribution, Population Structure, and Antimicrobial Resistance of Group B Streptococcus Strains Recovered from Colonized Pregnant Women

Using serotyping, multilocus sequence typing, and whole-genome sequencing (WGS) of selected strains, we studied the population structure of 102 group B Streptococcus (GBS) isolates prospectively sampled in 2014 from vaginal/rectal swabs of healthy pregnant women in metropolitan Toronto, Canada. We also determined the susceptibilities of each of the colonizing isolates to penicillin, erythromycin, clindamycin, tetracycline, and other antimicrobial agents. Overall, we observed a high rate of tetracycline resistance (89%) among colonizing GBS isolates. We found resistance to erythromycin in 36% of the strains, and 33% were constitutively or inducibly resistant to clindamycin. The most frequently identified serotypes were III (25%), Ia (23%), and V (19%). Serotype IV accounted for 6% of the colonizing isolates, a rate consistent with that observed among patients with invasive GBS infections in metropolitan Toronto. The majority of serotype IV isolates belonged to sequence type (ST)459, a tetracycline-, erythromycin-, and clindamycin-resistant ST first identified in Minnesota, which is considered to be the main driver of serotype IV GBS expansion in North America. WGS revealed that ST459 isolates from Canada are clonally related to colonizing and invasive ST459 organisms circulating in regions of the United States. We also used WGS to study recombination in selected colonizing strains from metropolitan Toronto, which revealed multiple episodes of capsular switching. Present and future circulating GBS organisms and their genetic diversity may influence GBS vaccine development.

Shigella: A Highly Virulent and Elusive Pathogen

Despite a significant decrease in Shigella-related mortality, shigellosis continues to carry a significant burden of disease worldwide, particularly in Asia and Africa. Shigella is a highly virulent pathogen comprised of four major species with numerous subtypes. Shigella dysenteriae and Shigella flexneri infections are predominant in resource-limited settings. Clinical presentations range from mild watery diarrhea to severe dysentery with systemic complications such as electrolyte imbalance, seizures and hemolytic uremic syndrome. S. dysenteriae subtype 1, the producer of Shiga toxin, causes the most severe illness and highest mortality. Susceptible strains of Shigella may be effectively treated with inexpensive oral antibiotics such as ampicillin or trimethoprim-sulfamethoxazole. Unfortunately, multidrug resistant strains have emerged that have rendered most antibiotics, including fluoroquinolones and extended-spectrum cephalosporins, ineffective. Management and prevention of shigellosis represents a major public health challenge. The development of an effective vaccine is urgently needed to decrease its global impact.