restriction enzymes

[Markus Schneemann]

Hi all:

I'm looking for a restriction enzyme that cuts human (eukaryotic)
genomic DNA into smaller pieces than it does with bacterial (gram +
actinomyces, GC-rich) chromosomal DNA.
The purpose is to generate a bacterial chromosomal library from
intracellularly grown bacteria (grown inside human macrophages) and to get
rid of the human genomic DNA that may contaminate the bacterial DNA.
If the human DNApieces are considerably smaller (let's say, below 10-15kb)
than the bacterial ones (>25kb) the packaging of cosmids (Stratagene
SuperCos) should exclude any DNA below 20kb (so they promise...).
Does anybody know of such a restriction enzyme ? 
Or of a easily to deactivate DNAse ?

Cheers,

Markus
schneema at cmgm.stanford.edu