Detection and characterization of extended-spectrum {beta}-lactamases among bloodstream isolates of Enterobacter spp. in Hong Kong, 2000-2002

<it>Objectives</it>: A total of 139 consecutive and non-duplicate bloodstream isolates of <it>Enterobacter</it> spp. collected from inpatients in Hong Kong during 2000–2002 were studied for production of extended-spectrum β-lactamases (ESBLs). <it>Methods</it>: All isolates were evaluated by the modified double-disc synergy test (m-DDST), the combined disc method (CDM) and the three-dimensional (3D) test. The m-DDST and CDM were modified by the use of cefepime discs. β-Lactamases were characterized by isoelectric focusing and PCR sequencing using specific primers. <it>Results</it>: ESBLs were identified in nine isolates (overall 6.5%), including seven of 39 (17.9%) <it>Enterobacter hormaechei</it>, one of 27 (3.7%) <it>Enterobacter aerogenes</it> and the only <it>Enterobacter intermedius</it> strain. The <it>E. intermedius</it> strain was positive only in the 3D test but not in the other two tests. The other eight strains were positive in all three tests. No ESBL was detected in the other species, including non-<it>hormaechei</it> members of the <it>Enterobacter cloacae</it> complex (<it>n</it>=61), <it>Enterobacter agglomerans</it> (<it>n</it>=7), <it>Enterobacter gergoviae</it> (<it>n</it>=4) and <it>Enterobacter sakazakii</it> (<it>n</it>=1). The ESBL content included five different CTX-M enzymes (CTX-M-9, CTX-M-13, CTX-M-14, CTX-M-24 and a novel CTX-M-2-like β-lactamase), SHV-12 (<it>n</it>=2) and unidentifiable ESBLs with a pI of 7.7 or 7.9 in two strains. The seven ESBL-producing <it>E. hormaechei</it> were genotyped by pulsed-field gel electrophoresis and were found to be unrelated to each other. In three of the CTX-M-producing strains, IS<it>Ecp1</it>-like elements, including promoters for the β-lactamase gene, were found. <it>Conclusions</it>: Our data underscore the diversity of CTX-M enzymes among <it>Enterobacter</it> spp. in Hong Kong.