Exact matching in a query

I have a need for a layer of access control when performing a query on
the ferret index. The solution is to add an additional clause (e.g. -
access_teams:12 OR 13 OR 14 OR 22 OR 1). In order for this to work, I
need exact matching. This query does not perform an exact match. It
appears if the index record has access_teams=2 the query will return
this record.

Can someone help me with the syntax for exact matching?