Genetic and biochemical characterization of the chromosome-encoded class B β-lactamases from Shewanella livingstonensis (SLB-1) and Shewanella frigidimarina (SFB-1)

OBJECTIVES: To determine the beta-lactamase gene content of beta-lactam-susceptible psychrophilic gram-negative bacilli, Shewanella frigidimarina and Shewanella livingstonensis, isolated from a marine environment. METHODS: Beta-lactamase genes were cloned, sequenced and expressed in Escherichia coli. Kinetic parameters were determined using purified enzymes. RESULTS: Metallo-beta-lactamases SLB-1 and SFB-1 were identified from S. livingstonensis and S. frigidimarina, respectively, sharing 65% amino acid identity and being distantly related to other Ambler class B beta-lactamases (40 and 36% amino acid identity with GIM-1 and IMP-1 from Pseudomonas aeruginosa, respectively). SLB-1 had an EDTA-inhibited and broad-spectrum beta-lactam hydrolysis profile, whereas SFB-1 did not hydrolyse cephalosporins, with activity being weakly inhibited by EDTA and dipicolinic acid. CONCLUSIONS: This work provides further evidence that psychrophilic bacterial species may constitute a reservoir of beta-lactam resistance genes.