A novel type of AmpC beta-lactamase, ACC-1, produced by a Klebsiella pneumoniae strain causing nosocomial pneumonia

A Klebsiella pneumoniae strain resistant to oxyimino cephalosporins was cul tured from respiratory secretions of a patient suffering from nosocomial pn eumonia in Kiel, Germany, in 1997, The isolate harbors a bla resistance gen e located on a transmissible plasmid, An Escherichia coli transconjugant pr oduces a beta-lactamase with an isoelectric point of 7.7 and a resistance p henotype characteristic of an AmpC (class 1) beta-lactamase except for low MICs of cephamycins. The bla gene was cloned and sequenced. It encodes a pr otein of 386 amino acids with the active site serine of the S-X-X-K motif a t position 64, as is characteristic for class C beta-lactamases. Multiple a lignment of the deduced amino acid sequence with 21 other AmpC beta-lactama ses demonstrates only very distant homology, reaching at maximum 52.3% iden tity for the chromosomal AmpC beta-lactamase of Serratia marcescens SR50, T he beta-lactamase of K, pneumoniae KUS represents a new type of AmpC-class enzyme, for which we propose the designation ACC-1 (Ambler class C-1).