BEL-1, a novel clavulanic acid-inhibited extended-spectrum β-lactamase, and the class 1 integron In120 in Pseudomonas aeruginosa

Screening by a double-disk synergy test identified a Pseudomonas aeruginosa isolate that produced a clavulanic acid-inhibited expanded-spectrum beta-lactamase (ESBL). Cloning and sequencing identified a novel ESBL, BEL-1, weakly related to other Ambler class A ESBLs. beta-Lactamase BEL-1 hydrolyzed significantly most expanded-spectrum cephalosporins and aztreonam, and its activity was inhibited by clavulanic acid, tazobactam, cefoxitin, moxalactam, and imipenem. This chromosome-encoded ESBL gene was embedded in a class I integron containing three other gene cassettes. In addition, this integron was bracketed by Tn1404 transposon sequences at its right end and by P. aeruginosa-specific sequences at its left end.