Mechanisms of genome evolution of Streptococcus

Abstract

The genus Streptococcus contains 104 recognized species, many of which are associated with human or animal hosts. A globally prevalent human pathogen in this group is Streptococcus pneumoniae (the pneumococcus). While being a common resident of the upper respiratory tract, it is also a major cause of otitis media, pneumonia, bacteremia and meningitis, accounting for a high burden of morbidity and mortality worldwide. Recent findings demonstrate the importance of recombination and selection in driving the population dynamics and evolution of different pneumococcal lineages, allowing them to successfully evade the impacts of selective pressures such as vaccination and antibiotic treatment. We highlight the ability of pneumococci to respond to these pressures through processes including serotype replacement, capsular switching and horizontal gene transfer (HGT) of antibiotic resistance genes. The challenge in controlling this pathogen also lies in the exceptional genetic and phenotypic variation among different pneumococcal lineages, particularly in terms of their pathogenicity and resistance to current therapeutic strategies. The widespread use of pneumococcal conjugate vaccines, which target only a small subset of the more than 90 pneumococcal serotypes, provides us with a unique opportunity to elucidate how the processes of selection and recombination interact to generate a remarkable level of plasticity and heterogeneity in the pneumococcal genome. These processes also play an important role in the emergence and spread of multi-resistant strains, which continues to pose a challenge in disease control and/or eradication. The application of population of genomic approaches at different spatial and temporal scales will help improve strategies to control this global pathogen, and potentially other pathogenic streptococci.

Similar genomic patterns of clinical infective endocarditis and oral isolates of Streptococcus sanguinis and Streptococcus gordonii

“…This was 75 additional pan-genomic families compared to the study of Zheng et al 41 , which is surprisingly few, since this study included three times the number of genomes. Previous studies have shown that Streptococcus has an open pan-genome and frequent recombination that leads to gene gain and loss within Streptococcus 8,41,45 . Therefore, the size of the pan-genome is expected to increase as the number of genomes increases.…”

“…Natural genetic transformation, by uptake as well as release of DNA, has been described in several species belonging to the Mitis Group streptococci 1,7 . This genetic competence is an important mechanism for acquiring genes involved in biofilm formation, adherence and resistance to host immune systems [7][8][9] .…”

Immunization, Antibiotic Use, and Pneumococcal Colonization Over a 15-Year Period

“…28,29 Next we observed rapid reductions in certain additional PCV13 serotypes ∼3 years after introduction of PCV13, although, notably, serotypes 19A and 3 continued to be present at low rates in 2014. Possible reasons for the persistence of 19A and 3 include genetic diversity leading to less effective immune responses 22,30,31 or selection pressure from recent antibiotic use. 32 -34 Of note, first-line penicillins continue to be the most frequently prescribed antibiotic across all age groups among young children in Massachusetts, which may result in the continued success of 19A associated with penicillin resistance.…”

A Cross-Reactive Protein Vaccine Combined with PCV-13 Prevents Streptococcus pneumoniae- and Haemophilus influenzae-Mediated Acute Otitis Media

“…Highly conserved surface proteins of the pneumococcus are also attractive vaccine candidates, although the diverse pangenome of pneumococcus (43), especially that of the nontypeable strains (47), can result in a diverse repertoire of surface proteins among strains (43). Therefore, multivalent vaccines may have the greatest potential to provide the broadest protection against multiple serotypes and nonencapsulated pneumococci.…”