DETECTION OF EXTENDED-SPECTRUM-BETA-LACTAMASE-PRODUCING MEMBERS OF THE FAMILY ENTEROBACTERIACEAE WITH THE VITEK ESBL TEST

A three-phase analysis of the Vitek ESBL test and a double-disk (2-dis k) test was performed to assess their ability to detect extended-spect rum beta-lactamases (ESBLs) in members of the family Enterobacteriacea e. In the first two phases involving detection of ESBLs in 157 strains possessing well-characterized beta-lactamases, sensitivity and specif icity were found to be 99.5 and 100%, respectively, for the Vitek ESBL test and 98.1 and 99.4%, respectively, for the 2-disk test. In the th ird phase, in which the ability of each test to detect ESBLs in 295 cl inical isolates was assessed, there was only one false positive (Vitek ESBL test). Across all three phases, the Vitek ESBL test was found to be much easier to perform than the 2-disk test. The latter also invol ved subjective interpretation of results. There were a total of 176 Es cherichia coli and 157 Klebsiella pneumoniae isolates and less than 40 isolates of each of 14 other species evaluated. In a supplemental stu dy of Klebsiella oxytoca, an organism possessing a chromosomal beta-la ctamase similar to an ESBL, the Vitek ESBL test was found to be capabl e of detecting hyperproduction of this enzyme in strains of this speci es as well. These data indicate that the Vitek ESBL test is reliable f or the detection of ESBLs in E. coli and K. pneumoniae, the two specie s in which ESBLs are most common, and of hyperproduction of the K. oxy toca beta-lactamase, a situation which engenders a level of resistance to this species similar to that seen with ESBLs.