Genetic linkage of the penicillinase gene, amp, and blrAB, encoding the regulator of beta-lactamase expression in Aeromonas spp.
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).
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.
Pannika
P
Niumsup
Alan M
AM
Simm
Kurshid
K
Nurmahomed
Timothy R
TR
Walsh
Peter M
PM
Bennett
Matthew B
MB
Avison
D000333:Aeromonas / Q000201:enzymology / Q000235:genetics*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D008040:Genetic Linkage / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D010405:Penicillinase / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics*
D001426:Bacterial Proteins; C104885:BlrA protein, Aeromonas jandaei; D002352:Carrier Proteins; D010405:Penicillinase; D001618:beta-Lactamases; C108449:oxacillinase