RAHN-2, a chromosomal extended-spectrum class A β-lactamase from Rahnella aquatilis

Abstract

Objectives: Rahnella aquatilis is an environmental enterobacterial species with a chromosomal blaRAHN-1 gene encoding extended-spectrum class A β-lactamase RAHN-1. We describe the diversity of blaRAHN genes from two groups of strains, G1 and G2, isolated from raw fruits and vegetables, and the new class A β-lactamase RAHN-2. Methods: MICs were determined by Etest. blaRAHN genes were amplified by PCR, sequenced, and cloned to produce RAHN-1 and RAHN-2 proteins whose kinetic parameters were determined. Results: All strains had similar β-lactam resistance patterns. However, isolates of G1 were at least 2-fold more susceptible to piperacillin, amoxicillin, piperacillin/clavulanic acid, piperacillin/tazobactam and cefotaxime. Sequences of blaRAHN from G1 had <82.9% identity with that of blaRAHN-1, whereas those of G2 were >92% identical. The RAHN-2 β-lactamase was 89.8% identical to RAHN-1, 5-fold more efficient than RAHN-1 in hydrolysing ticarcillin and 2.5-fold more efficient in cefotaxime and cefuroxime hydrolysis. However, the specific activity of RAHN-1 was 2-fold higher than that of RAHN-2 suggesting that the blaRAHN genes are regulated differently. Conclusions: The new class A β-lactamase RAHN-2 is phenotypically difficult to detect and requires MIC determination. © The Author 2010.