βlasEN: Microdilution Panel for Identifying β-Lactamases Present in Isolates of Enterobacteriaceae

Abstract

A dried investigational use-only microdilution panel named ␤lasEN (a short named derived from the panel's purpose, to identify ␤-lactamases in Enterobacteriaceae) containing 10 ␤-lactam drugs with and without ␤-lactamase inhibitors was developed to identify ␤-lactamases among clinical isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Citrobacter koseri, Citrobacter freundii group, Enterobacter spp., and Serratia marcescens. The MICs obtained with a collection of 383 organisms containing well-characterized ␤-lactamases were used to develop numeric codes and logic pathways for computerized analysis of results. The resultant logic pathways and ␤lasEN panel were then used to test and identify ␤-lactamases among 885 isolates of Enterobacteriaceae recovered in cultures obtained at six different hospital laboratories across the United States. ␤-Lactamases present in 801 (90.5%) of the 885 isolates were identified by ␤lasEN by using the existing logic pathways and codes or after minor modifications were made to the existing codes. The 84 strains that gave codes that ␤lasEN could not identify were collected, reidentified, and retested by using ␤lasEN. Three strains had been misidentified, 54 strains gave different codes upon repeat testing that could be identified by ␤lasEN, and 27 strains repeated new codes. The ␤-lactamases in these strains were identified, and the new codes were added to the ␤lasEN logic pathways. These results indicate that ␤lasEN can identify clinically important ␤-lactamases among most isolates of Enterobacteriaceae. The results also show that good quality control and attention to proper performance of the tests are essential to the correct performance of ␤lasEN.Over the past 10 years, there has been a significant increase in the numbers and types of ␤-lactamases encountered among clinical isolates of Enterobacteriaceae (4-7, 9, 14-16, 18, 23, 31, 37; H. Kurokawa et al., Letter, Lancet 354:955, 1999). Not only have the older plasmid-mediated ␤-lactamases such as TEM-1 and SHV-1 become more prevalent but also new derivatives of these enzymes capable of producing resistance to expandedspectrum ␤-lactam antibiotics have appeared (9,19). Plasmid derivatives of chromosomal ␤-lactamases have also appeared (2, 9, 14), as have enzymes capable of producing resistance to the carbapenems (9, 12, 22, 28; G. Cornaglia et al., Letter, Lancet 353:899-900, 1999). Unfortunately, many Enterobacteriaceae producing these new ␤-lactamases do not show frank resistance in routine susceptibility tests with certain ␤-lactam antibiotics despite clinical evidence that the drugs do not provide effective therapy (8,10,21,29,44). Thus, it has become imperative to design tests that will help microbiologists identify which ␤-lactamase(s) may be present in a clinical isolate of Enterobacteriaceae (8,11,12,17,20,25,33,34,(38)(39)(40).A series of studies have been performed to determine whether or not results of microdilution panels with or without ␤-lactamase inhibitors could be used to determine the presen...

Regional Occurrence of Plasmid‐Mediated SHV‐7, an Extended‐Spectrum β‐Lactamase, inEnterobacter cloacaein Philadelphia Teaching Hospitals

“…In 1988, in an outbreak of infections mainly due to ceftazidime-resistant, ESBL-producing K. pneumoniae in a Massachusetts long-term care facility, ESBLs, which subsequently were proven to be TEM-12 and TEM-26, were detected in the 2 E. cloacae isolates that were available for testing [14]. Sanders et al [15] identified ESBLs in 8 of 110 E. cloacae isolates from cultures obtained from 6 different hospital laboratories across the United States, and D'Agata et al [16] found SHV-3 ESBL in 3 of 69 E. cloacae isolates from surveillance cultures from patients in the surgical intensive care unit in a Boston tertiary care hospital.…”