Salmonella bacteria can contaminate food, causing Salmonellosis, a disease with symptoms such as diarrhea and abdominal cramps. Although treatable with antibiotics, the incidence and severity of Salmonellosis has increased over the last ten years, partially due to increased antibiotic resistance by some strains of the bacteria. Consequently, other methods of treatment or prevention are needed to better control these infections. Queenie Chan is investigating the potential to develop a vaccine for Salmonellosis. Vaccine design varies in difficulty, depending on the nature of the infectious agent. In the case of Salmonellosis, dendritic cells take up bacteria in the body and break the protein components down into small pieces (peptides) on the surface of the cells. These fragments retain the identity of the original bacteria. In theory, injecting bacterial fragments identical to those found on the surface of dendritic cells will prompt an immune response against the bacteria, without an actual infection. Chan is using an instrument called a mass spectrometer to simultaneously assess hundreds of these peptide fragments to determine which peptides elicit an immune response. Chan hopes these peptides will provide the foundation for creating a vaccine against Salmonellosis, thereby avoiding the use of antibiotic drugs that help perpetuate the growth of antibiotic-resistant bacteria.