Production of metal dependent β-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-β-lactamases. The β-lactamases produced by the clinical isolates all focused as doublet bands at pi 4.8/4.9, characteristic of the B. fragilis CfiA type metallo-β-lactamase. Each enzyme had a similar substrate profile and were inhibited by EDTA and activated with zinc sulphate. The sequence of the metallo-β-lactamase gene from B. fragilis ED262 was determined and confirmed to be a CfiA type β-lactamase. Consequently, the five isolates examined probably produce a CfiA type β-lactamase, suggesting that metallo-β-lactamases were present before the widespread use of carbapenems.