A method to identify a high affinity nucleic acid ligand to inhibit the
activity of a lactamase enzyme. The method comprises several steps that
initially involve preparing a candidate mixture of nucleic acids. The
candidate mixture of nucleic acids is then allowed to make contact with
the lactamase enzyme under controlled conditions of temperature, ionic
strength and pH; the combination forms a candidate-enzyme mixture. The
target nucleic acids are partitioned from the remainder of the candidate
mixture. The target nucleic acids that have been partitioned are
amplified to yield a pool of nucleic acids enriched with target nucleic
acid sequences. The enriched pool of target nucleic acids have a
relatively higher affinity and specificity for binding to the lactamase,
whereby nucleic acid ligand of the lactamase are identified. Nucleic acid
ligands that inhibit an activity of lactamase. The lactamase includes
class B, metallo-.beta.-lactamase.