Evaluation of Protein Channel-Attenuated Salmonella Vaccines

The long-term objective of the project involves developing live vaccines through heterologous gene-mediated inactivation, as obtained using colonization factor antigen I (CFA/I) in Salmonella. We suspect this attenuation is because of the overexpression of channel CfaC and not due to the fimbriae CfaBE, although CfaBE may enhance the channel-mediated attenuation. Since this attenuation strategy was not previously described, we questioned whether it could be utilized for Salmonella vaccine development. <P> Since conventional live vaccine development methods based on gene inactivation have been met with obstacles, this proposed study will generate Salmonella live vaccines for application in humans. As such, we set the following two Specific Aims: <P> Specific Aim 1: Examine whether the deletion of fimbrial subunits, the secretion apparatus, or both are responsible for the observed attenuation of wild-type Salmonella. <P> Specific Aim 2: Determine which of the deletion mutants of the cfa/I operon attenuates wild-type Salmonella and can therefore be used as a protective vaccine against salmonellosis. <P> To achieve these two aims, we will install CfaC channel in the Salmonella cell outer membrane (OM). The channeled Salmonella will be evaluated for cell extension via atomic force microscope (AFM), viability in various conditions, morphology via Field Emission Scanning Electron Microscopy (FESEM), in vitro virulence via macrophages, and in vivo virulence by mouse model. Since the channel CFA/I in cell OM allows 741 dalton erythromycin to enter, it will also permit other smaller molecules, such as water, ions, and toxic molecules to pass. Thus, cell OM osmotic balance will be partially lost, which will result in the attenuation of bacterial pathogens. This study will possibly develop new live vaccines against Salmonella for human usage. <P>PUBLIC HEALTH RELEVANCE: The proposed project entitled, 'Evaluation of Protein Channel-Attenuated Salmonella Vaccines' will construct a live vaccine that aims at preventing human salmonellosis. Salmonella enterica is a disease that causes a variety of food and water-borne illnesses, such as gastroenteritis and typhoid fever. It can infect a wide range of animal hosts and also humans. Of the three common Typhoid fever disease, S. Typhi alone is estimated to cause approximately 16 million cases, with 600,000 deaths annually worldwide and 600 fatalities recently occurring each year in the United States. To make the situation even worse, this disease has acquired resistance to the antibiotics previously used to treat it. Recently, our laboratory invented a new strategy for inactivating the Salmonella. This new strategy is totally different from the conventionally used virulence gene inactivation method. If demonstrated effective in Salmonella, this strategy will be also applicable to other enterobacteria, as well. Therefore, this project will benefit not only the USA but also other countries epidemic with salmonellosis.