Elimination of persistent vaccine bacteria of Salmonella enterica serovar Typhimurium in the guts of immunized mice by inducible expression of truncated YncE

Abstract

Orally administered vaccine bacteria usually persist for a period of time in the intestinal tracts of immunized individuals, and are excreted in feces to the environment resulting in a potential biosafety issue. The releasing risk can be minimized by immediate elimination of the persistent vaccine bacteria once adequate protective immune responses have been elicited by the vaccine bacteria. In a previous study, inducible expression of truncated yncE gene (yncE*) was found lethal to host bacteria. This feature has an application potential in biosafety control. Here, we assessed the efficacy of YncE* in eliminating an attenuated strain of Salmonella enterica serovar Typhimurium in a mouse model. To this end, a pBAD-derived plasmid containing yncE* under the control of the Ara promoter was transformed into a ΔphoPQ mutant of S. Typhimurium. Our data show that the induced expression of yncE* in the presence of arabinose eliminated the vaccine bacteria both in vitro and in vivo. BALB/c mice with or without streptomycin-pretreatment were used to assess the efficacy of YncE* in vivo. Oral administration of 500 μl of 20% arabinose at 24 h postvaccination removed the vaccine bacteria from the guts of the tested mice without streptomycin-pretreatment. For streptomycin-pretreated mice, which were colonized with higher levels of Salmonella, an additional gavage of arabinose was required to completely eliminate the vaccine bacteria in the guts of the tested mice. The orally administered arabinose did not affect the persistence of bacteria that had penetrated the intestinal mucosa of the immunized mice. Furthermore, there was no significant difference in the protection rate between the routine immunization and the immunization with the arabinose treatment. The results indicate that the yncE* element improves the biosafety of the bacterial vaccine, and can be taken in consideration in future design of live bacterial vaccines.

Small alarmones (p)ppGpp regulate virulence associated traits and pathogenesis ofSalmonella entericaserovar Typhi

“…Before infection with the RS-complemented Ty2ΔRelAΔSpoT strain, mice were orally administered with 20% arabinose as suggested previously (Wang et al, 2017). Before infection with the RS-complemented Ty2ΔRelAΔSpoT strain, mice were orally administered with 20% arabinose as suggested previously (Wang et al, 2017).…”

“…Mice were monitored for death over 7 days for lethal infection (2 × 10 7 CFU), and the survival data were plotted in a Kaplan-Meier graph. Before infection with the RS-complemented Ty2ΔRelAΔSpoT strain, mice were orally administered with 20% arabinose as suggested previously (Wang et al, 2017). To study systemic infection, 6-to 8-…”

Induction of Broad Immunity against Invasive Salmonella Disease by a Quadrivalent Combination Salmonella MAPS Vaccine Targeting Salmonella Enterica Serovars Typhimurium, Enteritidis, Typhi, and Paratyphi A

“…A potential concern, however, was that the bacteria were shed in the stool for up to 23 days after immunization, which poses a risk of infection in vulnerable people and an increased potential for transfer of genetic material [29,30]. S. Typhimurium have also been genetically modified to generate anti-LPS antibodies in mice, with limited fecal shedding [30][31][32][33].…”

Microbial Biocontainment Systems for Clinical, Agricultural, and Industrial Applications

“…However, methods were needed to limit the continuous proliferation of the bacteria inside the intestinal lumen or after evacuation. As a mean to address these concerns, MBSs from attenuated Salmonella typhimurium have been designed to include a toxin system (initially tested in Escherichia coli) which is activated upon ingestion of arabinose (Figure 3C) (Li et al, 2016;Wang et al, 2017).…”