SCO-1, a novel plasmid-mediated class A beta-lactamase with carbenicillinase characteristics from Escherichia coli

Abstract

A novel class A beta-lactamase (SCO-1) encoded by an 80-kb self-transferable plasmid from Escherichia coli is described. The interaction of SCO-1 with beta-lactams was similar to that of the CARB-type enzymes. Also, SCO-1 exhibited a 51% amino acid sequence identity with the RTG subgroup of chromosomal carbenicillinases (RTG-1, CARB-5, and CARB-8).

FIG. 1.

Schematic representation of the 3,833-bp Sau3A insert of the recombinant plasmid pSCO-1 encoding the β-lactamase SCO-1. Arrows indicate the translational orientation of the respective genes. Sizes of the respective nucleotide sequences and intervening regions are indicated below the schematic.

FIG. 2.

Amino acid sequence alignment of SCO-1 and six carbenicillinases, including those of the RTG subgroup (RTG-1, CARB-5, and CARB-8). The dashes indicate gaps introduced to optimize alignment. Asterisks show positions occupied by identical amino acid residues. Conservative amino acid substitutions are also indicated (+). Residues that are strictly conserved in class A β-lactamases are shown in boldface type. Shaded segments correspond to the structural elements characteristic of class A β-lactamases. The putative secretory peptide of SCO-1 is underlined. Ambler et al.'s numbering scheme was followed (1).