Abstract
Bacterial pathogens and commensals are surrounded by diverse surface polysaccharides which include capsules and lipopolysaccharides. These carbohydrates play a vital role in bacterial ecology and interactions with the environment. Here, we review recent rapid advancements in this field, which have improved our understanding of the roles, structures, and genetics of bacterial polysaccharide antigens. Genetic loci encoding the biosynthesis of these antigens may have evolved as bacterial diversity-generating machines, driven by selection from a variety of forces, including host immunity, bacteriophages, and cell–cell interactions. We argue that the high adaptive potential of polysaccharide antigens should be taken into account in the design of polysaccharide-targeting medical interventions like conjugate vaccines and phage-based therapies.
Highlights
Bacterial pathogens and commensals are surrounded by diverse surface polysaccharides which include capsules and lipopolysaccharides
The authors have argued that, for this reason, capsules have evolved as tools for environmental adaptation rather than as host-associated virulence factors. This is consistent with the fact that, amongst all discussed bacterial species, the most extensive capsular variation is found in gut microbes that behave as opportunistic pathogens, such as K. pneumoniae and
Phylogenetic and phylodynamic analyses revealed that these recombinants emerged prior to the introduction of the vaccine [39,54], implying that the polysaccharide capsule diversity evolves over time and that selection acts on this diversity
Summary
LOS phase variation ABC aMajor polysaccharide antigens of WHO global priority pathogens in need of new antibiotics, divided into three categories according to the urgency of need for new antibiotics: critical, high and medium priority. The presence of conserved genes at the flanking regions of the synthesis loci, like dexB/aliA in S. pneumoniae or galF/gnd in Klebsiella, promotes exchange of the entire locus by homologous recombination, which requires homology only at the flanks. Such changes facilitate serotype/antigen alterations between distant lineages without having to ‘invent’ a new combination, which has been widely documented in epidemiological studies [35,36,37,38,39,40,41,42,43].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
