First Detection of the Ambler Class C 1 AmpC β-Lactamase in Citrobacter freundii by a New, Simple Double-Disk Synergy Test

Abstract

ABSTRACT We report on the first detection of an AmpC-type Ambler class C 1 (ACC-1) β-lactamase in Citrobacter freundi isolated from a patient also harboring ACC-1-producing Escherichia coli and Klebsiella pneumoniae . We propose a simple cefoxitin-based double-disk synergy test (DDST) for the specific detection of ACC-1 in members of the family Enterobacteriaceae , including natural AmpC producers, in association with a cloxacillin-based DDST as a first-line AmpC-type β-lactamase screening test.