Study on an attenuated strain of Shigella sonnei S7 as a bacterial vaccine vector
Objective To study on the safety of a spontaneous mutant strain of Shigella sonnei S7 used as a living bacterial vaccine vector. Methods Making use of enterobacterial virulence and invasive test, DNA profile analysis and challenge test of rhesus monkey to determine the safety and stability of S7 and S7R. Results S7 can express high level S. sonnei O antigan and have immunogenicity; the invasive rate to HeLa cell was 4.3% and a virulent strain S. sonnei strain S512 was 83.6%. S7 did not express IpaA, B, C, D in Western bloting, and the large plasmid of S7 was stable after 36 passages. The phase Ⅰ large plasmid in S7 and the chalenge test in monkeys were different significantly from those of S512. Conclusion The strain S7 of S. sonnei as a living bacterial vaccine vector has its advantage. It is safe and its colony morphologic change can reflect the vector being with or without antigenicity. [