Production of metal dependent beta-lactamases by clinical strains of Bacteroides fragilis isolated before 1987.

Five imipenem resistant clinical isolates of Bacteroides fragilis isolated before 1987, were examined to determine if they produced metallo-beta-lactamases. The beta-lactamases produced by the clinical isolates all focused as doublet bands at pl 4.8/4.9, characteristic of the B. fragilis CfiA type metallo-beta-lactamase. Each enzyme had a similar substrate profile and were inhibited by EDTA and activated with zinc sulphate. The sequence of the metallo-beta-lactamase gene from B. fragilis ED262 was determined and confirmed to be a CfiA type beta-lactamase. Consequently, the five isolates examined probably produce a CfiA type beta-lactamase, suggesting that metallo-beta-lactamases were present before the widespread use of carbapenems.