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ABSTRACT Staphylococcus aureus is a clinically important bacterial pathogen that has become resistant to treatment with most routinely used antibiotics. Alternative strategies, such as vaccination and phage therapy, are therefore actively being investigated to prevent or combat staphylococcal infections. Vaccination requires that vaccine targets are expressed at sufficient quantities during infection so that they can be targeted by the host’s immune system. While our knowledge of in vitro expression levels of putative vaccine candidates is comprehensive, crucial in vivo expression data are scarce and promising vaccine candidates during in vitro assessment often prove ineffective in preventing S. aureus infection. Here, we show how a newly developed high-throughput quantitative reverse transcription-PCR (qRT-PCR) assay monitoring the expression of 84 staphylococcal genes encoding mostly virulence factors can inform the selection and design of effective vaccine candidates against staphylococcal infections. We show that this assay can accurately quantify mRNA expression levels of these genes in several host organs relying only on very limited amounts of bacterial mRNA in each sample. We selected two highly expressed genes, lukE and lukD, encoding pore-forming leukotoxins, to inform the design of detoxified recombinant proteins and showed that immunization with recombinant genetically detoxified LukED antigens conferred protection against staphylococcal skin infection in mice. Consequently, knowledge of in vivo-expressed virulence determinants can be successfully deployed to identify and select promising candidates for optimized design of effective vaccine antigens against S. aureus. Notably, this approach should be broadly applicable to numerous other pathogens. IMPORTANCE Vaccination is an attractive strategy for preventing bacterial infections in an age of increased antimicrobial resistance. However, vaccine development frequently suffers significant setbacks when candidate antigens that show promising results in in vitro experimentation fail to protect from disease. An alluring strategy is to focus resources on developing bacterial virulence factors that are expressed during disease establishment or maintenance and are critical for bacterial in-host survival as vaccine targets. While expression profiles of many virulence factors have been characterized in detail in vitro, our knowledge of their in vivo expression profiles is still scarce. Here, using a high-throughput qRT-PCR approach, we identified two highly expressed leukotoxins in a murine infection model and showed that genetically detoxified derivatives of these elicited a protective immune response in a murine skin infection model. Therefore, in vivo gene expression can inform the selection of promising candidates for the design of effective vaccine antigens.

Paolo Donato De Ciantis1, Kiran Yashpal2, James Henry3, Gurmit Singh11Department of Pathology and Molecular Pathology, 2Pain Research Laboratories, 3Department of Psychiatry and Behavioral Neurosciences, McMaster University, Hamilton, Ontario, CanadaPurpose: The objectives of this study were to establish and characterize a novel animal model of metastatic prostate cancer-induced bone pain.Methods: Copenhagen rats were injected with 106 MATLyLu (MLL) prostate cancer cells or phosphate-buffered saline by per cutaneous intra femoral injections into the right hind leg distal epiphysis. Over 13 days, rats progressively developed a tumor within the distal femoral epiphysis. On days 3, 7, 10, and 13 post injection, rats were subjected to the incapacitance and Randall–Selitto behavioral tests as they are believed to be indirect reflections of tumor induced pain. Ipsilateral hind limbs were subjected to X-ray and computed tomography (CT) scans and histological sections were stained with hematoxylin and eosin (H&E).Results: Intra femoral injections of MLL cells resulted in the progressive development of a tumor leading to bone destruction and nociceptive behaviors. Tumor development resulted in the redistribution of weight to the contralateral hind leg and significantly reduced the paw withdrawal threshold of the ipsilateral hind paw as observed via the incapacitance and Randall–Selitto tests, respectively. X-ray and computed tomography scans along with H&E stains indicated tumor-associated structural damage to the distal femur. This model was challenged with administration of meloxicam. Compared with vehicle-injected controls, the meloxicam-treated rats displayed smaller nociceptive responses as observed with the incapacitance and Randall–Selitto tests, suggesting that meloxicam was effective in reducing the pain-related symptoms displayed by model animals and that the model behaved in a predictable way to cyclooxygenase-2 treatment.Conclusions: This model is unique from other bone cancer models in that it is a comprehensive model utilizing a competent immune system with a syngeneic tumor. The model establishes a tool that will be useful to investigate mechanisms of cancer pain that are induced by cancer cells.Keywords: tumor, nociception, behavior, meloxicam

SslE, the Secreted and surface-associated lipoprotein from Escherichia coli, has recently been associated to the M60-like extracellular zinc-metalloprotease sub-family which is implicated in glycan recognition and processing. SslE can be divided into two main variants and we recently proposed it as a potential vaccine candidate. By applying a number of in vitro bioassays and comparing wild type, knockout mutant and complemented strains, we have now demonstrated that SslE specifically contributes to degradation of mucin substrates, typically present in the intestine and bladder. Mutation of the zinc metallopeptidase motif of SslE dramatically impaired E. coli mucinase activity, confirming the specificity of the phenotype observed. Moreover, antibodies raised against variant I SslE, cloned from strain IHE3034 (SslEIHE3034), are able to inhibit translocation of E. coli strains expressing different variants through a mucin-based matrix, suggesting that SslE induces cross-reactive functional antibodies that affect the metallopeptidase activity. To test this hypothesis, we used well-established animal models and demonstrated that immunization with SslEIHE3034 significantly reduced gut, kidney and spleen colonization by strains producing variant II SslE and belonging to different pathotypes. Taken together, these data strongly support the importance of SslE in E. coli colonization of mucosal surfaces and reinforce the use of this antigen as a component of a broadly protective vaccine against pathogenic E. coli species.

There is considerable interest in pneumococcal protein antigens capable of inducing serotype-independent immunoprotection and of improving, thereby, existing vaccines. We report here on the immunogenic properties of a novel surface antigen encoded by ORF spr1875 in the R6 strain genome. An antigenic fragment encoded by spr1875, designated R4, was identified using a Streptococcus pneumoniae phage displayed genomic library after selection with a human convalescent serum. Immunofluorescence analysis with anti-R4 antisera showed that Spr1875 was expressed on the surface of strains belonging to different serotypes. Moreover, the gene was present with little sequence variability in 27 different pneumococcal strains isolated worldwide. A mutant lacking Spr1875 was considerably less virulent than the wild type D39 strain in an intravenous mouse model of infection. Moreover, immunization with the R4 recombinant fragment, but not with the whole Spr1875 protein, induced significant protection against sepsis in mice. Lack of protection after immunization with the whole protein was related to the presence of immunodominant, non-protective epitopes located outside of the R4 fragment. In conclusion, our data indicate that Spr1875 has a role in pneumococcal virulence and is immunogenic. As the R4 fragment conferred immunoprotection from experimental sepsis, selected antigenic fragments of Spr1875 may be useful for the development of a pneumococcal protein-based vaccine.