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).
Niumsup
Pannika
P
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.
Simm
Alan M
AM
Nurmahomed
Kurshid
K
Walsh
Timothy R
TR
Bennett
Peter M
PM
Avison
Matthew B
MB
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