Why is sacB expression lethal in E. coli?

[someone]

Product of enzymatic conversion of sucrose by SacB causes death in many
gram-negatives by osmotic shock (cells burst).

M.A.

REWH Lab <rewhlab at cbdn.ca> wrote in article <53udca$jl1 at nntp.ucs.ubc.ca>...
> Hi,
> 	I can't find any reference to why sacB functions as a 
> counterselective marker in E. coli in the presence of 5-10% sucrose. 
Does 
> anyone know why it works?