A Novel Extended-Spectrum β-Lactamase, SGM-1, from an Environmental Isolate of Sphingobium sp.
Antimicrob Agents Chemother. 2013 May 28;
Authors: Lamoureaux TL, Vakulenko V, Toth M, Frase H, Vakulenko SB
SGM-1 is a novel class A β-lactamase from an environmental isolate of Sphingobium sp. containing all the distinct amino acid motifs of class A β-lactamases. It shares 77-80% amino acid sequence identity with putative β-lactamases that are present on the chromosome of all Sphingobium species whose genomes were sequenced and annotated. Thus SGM-type β-lactamases are native to this genus. Antibiotic susceptibility testing classifies SGM-1 as an extended-spectrum β-lactamase, conferring the highest level of resistance to penicillins. Although SGM-1 contains the conserved cysteine residues characteristic of class A carbapenemases, it does not confer resistance to the carbapenem antibiotics imipenem, meropenem, or doripenem, but does increase the MIC of ertapenem eight-fold. SGM-1 hydrolyzes penicillins and the monobactam aztreonam with similar catalytic efficiencies, ranging from 10(5) to 10(6) M(-1) s(-1). The catalytic efficiencies of SGM-1 for cefoxitin and ceftazidime were the lowest (10(2) to 10(3) M(-1) s(-1)) among the cephalosporins tested while the catalytic efficiencies against all other cephalosporins varied from about 10(5) to 10(6) M(-1) s(-1). SGM-1 exhibited measurable but not significant activity towards the carbapenems tested. SGM-1 also showed high affinity for clavulanic acid, tazobactam, and sulbactam (Ki < 1 μM), however only clavulanic acid significantly reduced the MICs of β-lactams.
PMID: 23716045 [PubMed - as supplied by publisher]