Molecular and Biochemical Characterization of the Natural Chromosome-Encoded Class A β-Lactamase from Pseudomonas luteola

Abstract

Pseudomonas luteola (formerly classified as CDC group Ve-1 and named Chryseomonas luteola) is an unusual pathogen implicated in rare but serious infections in humans. A novel beta-lactamase gene, bla(LUT-1), was cloned from the whole-cell DNA of the P. luteola clinical isolate LAM, which had a weak narrow-spectrum beta-lactam-resistant phenotype, and expressed in Escherichia coli. This gene encoded LUT-1, a 296-amino-acid Ambler class A beta-lactamase with a pI of 6 and a theoretical molecular mass of 28.9 kDa. The catalytic efficiency of this enzyme was higher for cephalothin, cefuroxime, and cefotaxime than for penicillins. It was found to be 49% to 59% identical to other Ambler class A beta-lactamases from Burkholderia sp. (PenA to PenL), Ralstonia eutropha (REUT), Citrobacter sedlakii (SED-1), Serratia fonticola (FONA and SFC-1), Klebsiella sp. (KPC and OXY), and CTX-M extended-spectrum beta-lactamases. No gene homologous to the regulatory ampR genes of class A beta-lactamases was found in the vicinity of the bla(LUT-1) gene. The entire bla(LUT-1) coding region was amplified by PCR and sequenced in five other genetically unrelated P. luteola strains (including the P. luteola type strain). A new variant of bla(LUT-1) was found for each strain. These genes (named bla(LUT-2) to bla(LUT-6)) had nucleotide sequences 98.1 to 99.5% identical to that of bla(LUT-1) and differing from this gene by two to four nonsynonymous single nucleotide polymorphisms. The bla(LUT) gene was located on a 700- to 800-kb chromosomal I-CeuI fragment, the precise size of this fragment depending on the P. luteola strain.