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 response to the use of late generation cephalosporins. In those hospitals where Klebsiella pneumoniae and other bacteria possessing these enzymes flourish, many interventions have been applied to reduce this trend. We instituted 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 interesting 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 responsible for ceftazidime resistance in our earlier described outbreak, was lacking in most of the isolates examined. Among the remaining ceftazidime-resistant K. pneumoniae, TEM-26 was also absent, and new enzymes that hydrolyze ceftazidime were detected. Loss of ceftazidime-hydrolyzing beta-lactamases was observed after in vitro passage of ceftazidime-resistant K. pneumoniae on antibiotic-free media. These findings suggest that class restriction of cephalosporins may increase susceptibility among extended-spectrum beta-lactamase-producing pathogens.