Detection of multiresistant ceftazidime-susceptible Klebsiella pneumoniae isolates lacking TEM-26 after class restriction of cephalosporins

A multitude of extended spectrum beta -lactamases (ESBLs) have evolved in r esponse to the use of late generation cephalosporins. In those hospitals wh ere Klebsiella pneumoniae and other bacteria possessing these enzymes flour ish, many interventions have been applied to reduce this trend. We institut ed a policy of class restriction of cephalosporins in our hospital in 1996 that led to a 44% reduction in ceftazidime-resistant K. pneumoniae hospital -wide and an 87% decrease in the surgical intensive care unit. Another inte resting outcome of this strategy was the identification of multiresistant K . pneumoniae, which was now susceptible to ceftazidime, Characterization of these novel isolates demonstrated that the TEM-26 enzyme, which was respon sible for ceftazidime resistance in our earlier described outbreak, was lac king in most of the isolates examined. Among the remaining ceftazidime-resi stant K. pneumoniae, TEM-26 was also absent, and new enzymes that hydrolyze ceftazidime were detected. Loss of ceftazidime-hydrolyzing beta -lactamase s was observed after in vitro passage of ceftazidime-resistant K. pneumonia e on antibiotic-free media. These findings suggest that class restriction o f cephalosporins may increase susceptibility among extended-spectrum beta - lactamase-producing pathogens.