Characterisation of KLUA-9, a β-lactamase from extended-spectrum cephalosporin-susceptible Kluyvera ascorbata, and genetic organisation of blaKLUA-9

This study characterised the genetic environment of the chromosomally encoded blaKLUA-9 gene from a clinical Kluyvera ascorbata isolate and performed a kinetic characterisation of KLUA-9. Purified KLUA-9 showed the highest catalytic efficacies towards benzylpenicillin, ampicillin, piperacillin, first-generation cephalosporins, cefuroxime and cefoperazone; like other ‘cefotaximases’, it showed a much higher rate of hydrolysis of cefotaxime than ceftazidime, whilst dicloxacillin, cefoxitin and imipenem behaved as poor substrates. A 9 kb insert from K. ascorbata was cloned (Escherichia coli KK68C1) and sequenced. blaKLUA-9 and its 266 bp upstream flanking region (almost identical to the integron-associated blaCTX-M-2) are preceded by an aspat variant, a ypdABC-like operon and two open reading frames with unknown functions. Unlike ISCR1-associated blaCTX-M-2 genes, we failed to detect the putative orf513 recombination sites. Instead, we were able to localise the 5 bp target sites for insertion of ISEcp1B, suggesting that this element could be responsible for future (or still undetected) mobilisation of blaKLUA-9 to more efficiently transferred elements.