title: Substitution of Thr for Ala-237 in TEM-17, TEM-12 and TEM-26: alterations in beta-lactam resistance conferred on Escherichia coli.
abstract: Non-naturally occurring mutants of TEM-17 (E104K), TEM-12 (R164S) and TEM-26 (E104K:R164S) extended-spectrum (ES) beta-lactamases bearing threonine at position 237 were constructed by site-specific mutagenesis and expressed under isogenic conditions in Escherichia coli. Quantification of beta-lactamase activities and immunoblotting indicated that Ala-237-->Thr did not significantly affect expression levels of these ES enzymes. Minimum inhibitory concentrations of beta-lactam antibiotics showed that the presence of threonine at position 237 exerted a dominant effect increasing the enzymes' preference for various early generation cephalosporins over penicillins. Activity against broad-spectrum oxyimino-beta-lactams was also changed. The effect of Ala-237-->Thr on the activity against ceftazidime, aztreonam, cefepime and cefpirome of all three ES TEM enzymes was detrimental. Introduction of Thr-237 improved activity against cefotaxime and ceftriaxone in TEM-12 and TEM-26, but not in TEM-17.
authors.affiliation: Laboratory of Bacteriology, Hellenic Pasteur Institute, Athens, Greece.
authors.forename: P
authors.initials: P
authors.lastname: Giakkoupi
authors.forename: A M
authors.initials: AM
authors.lastname: Hujer
authors.forename: V
authors.initials: V
authors.lastname: Miriagou
authors.forename: E
authors.initials: E
authors.lastname: Tzelepi
authors.forename: R A
authors.initials: RA
authors.lastname: Bonomo
authors.forename: L S
authors.initials: LS
authors.lastname: Tzouvelekis
mesh_terms: D000409:Alanine / Q000737:chemistry; D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D007526:Isoelectric Point; D008826:Microbial Sensitivity Tests; D016297:Mutagenesis, Site-Directed; D013912:Threonine / Q000737:chemistry; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D013912:Threonine; C088328:beta-lactamase TEM-12; C087312:beta-lactamase TEM-26; D001618:beta-Lactamases; D000409:Alanine