What quality control organisms should laboratories use for ESBL testing?
K. pneumoniae ATCC 700603 (positive control) and E. coli ATCC 25922 (negative control) should be used for quality control of ESBL tests (1). Top Can an ESBL be present in an isolate of K. pneumoniae that is resistant to ceftazidime and/or cefotaxime, but demonstrates no clavulanic acid effect in the phenotypic confirmatory test? Yes. The phenotypic confirmatory test does not detect all ESBLs. Some organisms with ESBLs contain other β-lactamases that can mask ESBL production in the phenotypic test, resulting in a false-negative test. These β-lactamases include AmpCs and inhibitor-resistant TEMs (IRTs). Hyper-production of TEM and/or SHV β-lactamases in organisms with ESBLs also may cause false-negative phenotypic confirmatory test results. Currently, detection of organisms with multiple β-lactamases that may interfere with the phenotypic confirmatory test can only be accomplished using isoelectric focusing and DNA sequencing, methods that are not usually available in clinical laboratori
