A novel method for the identification and distinction of the beta-lactamases of the genus Acinetobacter

The characterization of the chromosomal beta-lactamases of Acinetobacter has proved difficult because of the poor focusing of these enzymes in conventional isoelectric focusing on polyacrylamide gels. We describe a novel isoelectric focusing method, which employs an agarose gel incorporating a detergent with sorbitol and urea, to examine the beta-lactamases produced by eight clinical strains of Acinetobacter calcoaceticus; we have identified four different beta-lactamases. The molecular masses of each of the beta-lactamases was estimated and most of them ranged from 600,000 to greater than 1,000,000. These are the largest beta-lactamases so far described and their size is likely to be one reason for their poor solubility in conventional polyacrylamide systems.