Tightly regulated bacteriolysis for production of empty Salmonella Enteritidis envelope.

To avoid leaky expression of the bacterial host-toxic PhiX174 lysis gene E from the λpR promoter, a convergent promoter construct was made in which gene E was placed between a sense λpR promoter and an anti-sense P araBAD promoter. In the presence of l-arabinose, leaky transcription of lysis gene E at 28°C from the sense λpR promoter was repressed by an anti-sense RNA simultaneously expressed from the P araBAD promoter. The stringent repression of lysis gene E in the absence of induction temperature resulted into higher concentration of bacteria in culture suspension, and consequently higher and stable production of a Salmonella Enteritidis (S. Enteritidis) ghost. The immunogenicity of the S. Enteritidis ghost was evaluated by immunizing chickens. Chickens from the immunized group demonstrated a significant increase in the levels of S. Enteritidis-specific plasma IgG, intestinal sIgA, and lymphocyte proliferative response. After virulent S. Enteritidis challenge, the immunized group exhibited decreased bacterial recovery from organs compared with the non-immunized group. Together, these results demonstrate that the stringent molecular control over leaky transcription of lysis gene E enabled the stable production of S. Enteritidis ghost, and immunization with the S. Enteritidis ghost can protect chickens by inducing robust humoral and cellular immune responses.