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The bacterial pathogen Salmonella enterica serovar Typhimurium is one of the most common causes of foodborne disease in humans and is also an important model system for bacterial pathogenesis. Oral inoculation of C57Bl/6 mice, which are genetically susceptible to Salmonella, results in systemic infection but the murine intestine is not efficiently colonized unless the intestinal microbiota is disrupted. Pretreatment of C57Bl/6 mice with streptomycin, followed by oral inoculation with Salmonella Typhimurium results in colitis resembling human intestinal Salmonellosis. The predominant method of delivery of bacteria is oral gavage, during which organisms are deposited directly into the stomach via a feeding needle. Although convenient, this method can be stressful for mice, and may lead to unwanted tracheal or systemic introduction of bacteria. Here, we developed a method for oral infection of mice by voluntary consumption of regular mouse chow inoculated with bacteria. Mice readily ate chow fragments containing up to 108 CFU Salmonella, allowing for a wide range of infectious doses. In mice pretreated with streptomycin, infection with inoculated chow resulted in reproducible infections with doses as low as 103 CFU. Mice not treated with streptomycin, as well as resistant Nramp1 reconstituted C57Bl/6J mice, were also readily infected using this method. In summary, voluntary consumption of chow inoculated with Salmonella represents a natural route of infection for foodborne salmonellosis and a viable alternative to oral gavage. [ABSTRACT FROM AUTHOR]

Background: Chlamydia trachomatis is the etiological agent of trachoma the world's leading cause of infectious blindness. Here, we investigate whether protracted clearance of a primary infection in nonhuman primates is attributable to antigenic variation or related to the maturation of the anti-chlamydial humoral immune response specific to chlamydial antigens. Methodology/Principal Findings: Genomic sequencing of organisms isolated throughout the protracted primary infection revealed that antigenic variation was not related to the inability of monkeys to efficiently resolve their infection. To explore the maturation of the humoral immune response as a possible reason for delayed clearance, sera were analyzed by radioimmunoprecipitation using intrinsically radio-labeled antigens prepared under non-denaturing conditions. Antibody recognition was restricted to the antigenically variable major outer membrane protein (MOMP) and a few antigenically conserved antigens. Recognition of MOMP occurred early post-infection and correlated with reduction in infectious ocular burdens but not with infection eradication. In contrast, antibody recognition of conserved antigens, identified as PmpD, Hsp60, CPAF and Pgp3, appeared late and correlated with infection eradication. Partial immunity to re-challenge was associated with a discernible antibody recall response against all antigens. Antibody recognition of PmpD and CPAF was destroyed by heat treatment while MOMP and Pgp3 were partially affected, indicating that antibody specific to conformational epitopes on these proteins may be important to protective immunity. Conclusions/Significance: Our findings suggest that delayed clearance of chlamydial infection in NHP is not the result of antigenic variation but rather a consequence of the gradual maturation of the C. trachomatis antigen-specific humoral immune response. However, we cannot conclude that antibodies specific for these proteins play the primary role in host protective immunity as they could be surrogate markers of T cell immunity. Collectively, our results argue that an efficacious subunit trachoma vaccine might require a combination of these antigens delivered in their native conformation. [ABSTRACT FROM AUTHOR]