Listeria monocytogenes Mutants Carrying Newcastle Disease Virus F Gene Fused to its actA and p1cB : In vitro Expression and Immunogenicity in Chickens

Recombinant Listeria monocytogenes mutants carrying Newcastle disease virus (NDV) fusion protein gene F were constructed by homologous recombination. NDV F or its truncated fragment Fa was used as the model heterologous gene to be integrated into act A or p1cB downstream of their signal sequences. Correct orientation of the inserted genes was verified by polymerase chain reaction amplification of For Fa. The inserted F and Fa were expressed in the two recombinants Lm‐δactA‐F and Lm‐δp1cB‐Fa as shown by sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and Western blot. Both recombinants exhibited reduced virulence to embryonated eggs and mice by about 1.5–2.5 logs as compared with the parent wild strain 10403S. They were also less invasive than strain 10403S ( P < 0.05). Chickens receiving the recombinant strains orally or intraperitoneally were partially protected from virulent NDV challenge possibly due to enhancement of non‐specific immunity because the antibody titers against the homologous virus strain or the recombinant truncated fusion protein were marginal. Further research is needed in other animal models to see if the low antibody response results from insufficient expression of the heterologous genes as a result of failure of L. monocytogenes or its recombinants to persist or replicate in chickens. Edited by Minghua XU