High prevalence of extended-spectrum beta-lactamase-producing strains among blood isolates of Enterobacter spp. collected in a tertiary hospital during an 8-year period and their antimicrobial susceptibility patterns.

Of 72 blood isolates of Enterobacter spp. collected over an 8-year period, 50% (36 of 72) were derepressed or partially derepressed AmpC mutants. The extended-spectrum beta-lactamase (ESBL) production rate was 43% (31 of 72 isolates), and 67.3% (31 of 46) of extended-spectrum cephalosporin-resistant strains produced ESBLs. Thus, a confirmatory test for ESBL production is necessary for extended-spectrum cephalosporin-resistant Enterobacter spp.