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J Antimicrob Chemother. 2003 Jun;51(6):1351-8. Epub 2003 May 13.

Genetic linkage of the penicillinase gene, amp, and blrAB, encoding the regulator of beta-lactamase expression in Aeromonas spp.

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Bristol Centre for Antimicrobial Research and Evaluation, Department of Pathology and Microbiology, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK.


Aeromonas hydrophila T429125, a human clinical isolate, possesses three coordinately inducible beta-lactamases encoded by ampH (class D beta-lactamase), cepH (class C beta-lactamase) and imiH (class B beta-lactamase). We report that upstream of ampH there are two genes, blrA and blrB, encoding a putative two-component regulatory system. PCR studies revealed the same blrAB-amp gene arrangement in all Aeromonas spp. isolates tested; namely, Aeromonas veronii bv. sobria, Aeromonas jandaei, Aeromonas mediae, Aeromonas salmonicida and Aeromonas trota. A dominant mutation in the predicted BlrB kinase domain results in beta-lactamase overexpression in A. hydrophila T429125, but in other beta-lactamase-overexpressing mutants blrAB remains intact. Relative to the parent strain, A. hydrophila T429125, beta-lactamase- overexpressing mutants show a clear hierarchy of increased beta-lactamase expression: ImiH > CepH > AmpH. The same hierarchy is seen following beta-lactam challenge of A. hydrophila T429125, and correlates with the number of blr-tag sequences (TTCAC) found upstream of each beta-lactamase gene: ampH (one), cepH (two) and imiH (three).

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