help with laarge plasmids

[M.A.Schmidt]

Hi out there,
we are in need of a good reliable methods for the isolation of large
plasmids (> 150 kb) from E.coli. We have already tried a number of
techniques but nothing came of it. Does anyone know or has experience with
these large plasmids and could help us with a suggestion? It would help us
quite a lot and would be really appreciated! With many thanks 
M.Alexander Schmidt