Abstract
Outer membrane vesicles (OMV) derived from Bordetella pertussis—the etiologic agent of the resurgent disease called pertussis—are safe and effective in preventing bacterial colonization in the lungs of immunized mice. Vaccine formulations containing those OMV are capable of inducing a mixed Th1/Th2/Th17 profile, but even more interestingly, they may induce a tissue-resident memory immune response. This immune response is recommended for the new generation of pertussis-vaccines that must be developed to overcome the weaknesses of current commercial acellular vaccines (second-generation of pertussis vaccine). The third-generation of pertussis vaccine should also deal with infections caused by bacteria that currently circulate in the population and are phenotypically and genotypically different [in particular those deficient in the expression of pertactin antigen, PRN(-)] from those that circulated in the past. Here we evaluated the protective capacity of OMV derived from bacteria grown in biofilm, since it was observed that, by difference with older culture collection vaccine strains, circulating clinical B. pertussis isolates possess higher capacity for this lifestyle. Therefore, we performed studies with a clinical isolate with good biofilm-forming capacity. Biofilm lifestyle was confirmed by both scanning electron microscopy and proteomics. While scanning electron microscopy revealed typical biofilm structures in these cultures, BipA, fimbria, and other adhesins described as typical of the biofilm lifestyle were overexpressed in the biofilm culture in comparison with planktonic culture. OMV derived from biofilm (OMVbiof) or planktonic lifestyle (OMVplank) were used to formulate vaccines to compare their immunogenicity and protective capacities against infection with PRN(+) or PRN(-) B. pertussis clinical isolates. Using the mouse protection model, we detected that OMVbiof-vaccine was more immunogenic than OMVplank-vaccine in terms of both specific antibody titers and quality, since OMVbiof-vaccine induced antibodies with higher avidity. Moreover, when OMV were administered at suboptimal quantity for protection, OMVbiof-vaccine exhibited a significantly adequate and higher protective capacity against PRN(+) or PRN(-) than OMVplank-vaccine. Our findings indicate that the vaccine based on B. pertussis biofilm-derived OMV induces high protection also against pertactin-deficient strains, with a robust immune response.
Highlights
Pertussis, a highly contagious respiratory disease mainly caused by the Gram-negative bacterium Bordetella pertussis, has resurged in many countries even in those with high vaccination coverage [1,2,3,4,5]
Based on a relatively recent report on the higher capacity of Argentinian B. pertussis clinical isolates to form biofilms in comparison with reference strains adapted to laboratory growth condition [30] we decided to perform this study with the BpAR106 clinical isolate, which was sequenced and characterized by our group, possesses the ptxP3, ptxA1, prn2 genotype, and expresses pertactin [45]
In agreement to the findings reported by de Gouw et al [32] and Dorji et al [33], functional analysis using B. pertussis database showed that proteins involved in cell envelope, energy metabolism and protein synthesis were significantly overproduced in biofilm cells compared to planktonic cells (Figure 3B)
Summary
A highly contagious respiratory disease mainly caused by the Gram-negative bacterium Bordetella pertussis, has resurged in many countries even in those with high vaccination coverage [1,2,3,4,5]. Whole cell vaccines (wP) based on standardized cultures of B. pertussis strains and acellular vaccines (aP) composed of two (pertussis toxin and filamentous hemagglutinin), three (pertussis toxin, filamentous hemagglutinin and pertactin) or five (pertussis toxin, filamentous hemagglutinin, pertactin and fimbriae-2 and -3) immunogens are available. These vaccines manifest some weaknesses, such as the reactogenicity associated to wP or the faster waning immunity induced by aP [9, 10]. This new generation of vaccines must be i) safer than wP, ii) able to induce an immune response profile that is mostly Th1 and Th17 [12] with proliferation of the memory cell population resident in tissues [13, 14], iii) made up of multiple epitopes to minimize the selection pressure that it may exert on the circulating bacterial population, iv) able to protect against the circulating bacterial population, and v) biotechnologically easy to produce, ensuring accessibility to the entire population [5, 15]
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