Pseudomonas aeruginosaantigens as potential vaccines

Abstract

Pseudomonas aeruginosa is one of the most important opportunistic bacterial pathogens in humans and animals. This organism is ubiquitous and has high intrinsic resistance to antibiotics due to the low permeability of the outer membrane and the presence of numerous multiple drug efflux pumps. Various cell-associated and secreted antigens of P. aeruginosa have been the subject of vaccine development. Among pseudomonas antigens, the mucoid substance, which is an extracellular slime consisting predominantly of alginate, was found to be heterogenous in terms of size and immunogenicity. High molecular mass alginate components (30-300 kDa) appear to contain conserved epitopes while lower molecular mass alginate components (10-30 kDa) possess conserved epitopes in addition to unique epitopes. Surface-exposed antigens including O-antigens (O-specific polysaccharide of LPS) or H-antigens (flagellar antigens) have been used for serotyping due to their highly immunogenic nature. Chemical structures of repeating units of O-specific polysaccharides have been elucidated and these data allowed the identification of 31 chemotypes of P. aeruginosa. Conserved epitopes among all serotypes of P. aeruginosa are located in the core oligosaccharide and the lipid A region of LPS and immunogens containing these epitopes induce cross-protective immunity in mice against different P. aeruginosa immunotypes. To examine the protective properties of OM proteins, a vaccine containing P. aeruginosa OM proteins of molecular masses ranging from 20 to 100 kDa has been used in pre-clinical and clinical trials. This vaccine was efficacious in animal models against P. aeruginosa challenge and induced high levels of specific antibodies in human volunteers. Plasma from human volunteers containing anti-P. aeruginosa antibodies provided passive protection and helped the recovery of 87% of patients with severe forms of P. aeruginosa infection. Vaccines prepared from P. aeruginosa ribosomes induced protective immunity in mice, but the efficacy of ribosomal vaccines in humans is not yet known. A number of recent studies indicated the potential of some P. aeruginosa antigens that deserve attention as new vaccine candidates. The outer core of LPS was implicated to be a ligand for binding of P. aeruginosa to airway and ocular epithelial cells of animals. However, heterogeneity exists in this outer core region among different serotypes. Epitopes in the inner core are highly conserved and it has been demonstrated to be surface-accessible, and not masked by O-specific polysaccharide. The use of an in vivo selection/expression technology (IVET) by a group of researchers identified a number of P. aeruginosa proteins that are expressed in vivo and essential for virulence. Two of these in vivo-expressed proteins are FptA (ferripyochelin receptor protein) and a homologue of an LPS biosynthetic enzyme. Our laboratory has identified a highly conserved protein, WbpM, and P. aeruginosa with a deficiency in this protein produces only rough LPS and became serum sensitive. Res...

Lipopolysaccharide Endotoxins

“…As a result, some features of the outer-core structure were not identified in initial analyses (178). The limited structural variation in the core oligosaccharide within a genus is in striking contrast to the hypervariable O polysaccharides and has stimulated interest in the possibility of targeting the core oligosaccharides to generate immunotherapeutic antibodies (181)(182)(183)(184)(185). Similarly, the enzymes responsible for the conserved structural features in inner cores provide potential targets for novel therapeutics.…”

WbpO, a UDP-N-acetyl-d-galactosamine Dehydrogenase from Pseudomonas aeruginosa Serotype O6

“…(13), and Vibrio anguillarum (12); as well as capsular polysaccharide of Salmonella typhi (18), Staphylococcus aureus (19), and Vibrio vulnificus (11,15). Although the genes that are involved in the biosynthesis of ␣-D-GalNAcA have been described in a few studies (1,18,19), the enzyme activities of these gene products have not been elucidated. At present UDP-GalNAcA is not commercially available; therefore, a better understanding of the enzyme involved in the synthesis of this uronic acid sugar would provide the methodology for its production.…”

Application of Whole-Genome Sequencing Data for O-Specific Antigen Analysis and In Silico Serotyping of Pseudomonas aeruginosa Isolates

“…Previously, serotyping was a benchmark typing method for P. aeruginosa. In the 1980s, the International Antigenic Typing Scheme (IATS) was established to classify the species P. aeruginosa into 20 serotypes (O1 to O20) (5)(6)(7). Today, serotyping is infrequently used in the clinic for typing purposes, mainly because of the time-consuming protocol, the need for a continuous supply of serotype-specific antisera, and a high prevalence of polyagglutinating or nontypeable isolates.…”