Integron-Located<i>oxa-32</i>Gene Cassette Encoding an Extended-Spectrum Variant of OXA-2 β-Lactamase from<i>Pseudomonas aeruginosa</i>

A novel OXA-type enzyme, named OXA-46, was found to be encoded by a gene cassette inserted into a class 1 integron from a multidrug-resistant Pseudomonas aeruginosa clinical isolate. The variable region of the integron also contained a bla VIM-1 metallo-␤-lactamase cassette and a duplicated aacA4 aminoglycoside acetyltransferase cassette. OXA-46 belongs to the OXA-2 lineage of class D ␤-lactamases. It exhibits 78% sequence identity with OXA-2 and the highest similarity (around 92% identity) with another OXA-type enzyme detected in clinical isolates of Burkholderia cepacia and in unidentified bacteria from a wastewater plant. Expression of bla OXA-46 in Escherichia coli decreased susceptibility to penicillins and narrow-spectrum cephalosporins but not to extended-spectrum cephalosporins, cefsulodin, aztreonam, or carbapenems. The enzyme was overproduced in E. coli and purified by two anion-exchange chromatography steps (approximate yield, 6 mg/liter). OXA-46 was made of a 28.5-kDa polypeptide and exhibited an alkaline pI (7.8). In its native form OXA-46 appeared to be dimeric, and the oligomerization state was not affected by EDTA. Kinetic analysis of OXA-46 revealed a specificity for narrow-spectrum substrates, including oxacillin, other penicillins (but not temocillin), and narrow-spectrum cephalosporins. The enzyme apparently did not interact with temocillin, oxyimino-cephalosporins, or aztreonam. OXA-46 was inactivated by tazobactam and carbapenems and, although less efficiently, also by clavulanic acid. Enzyme activity was not affected either by EDTA or by divalent cations and exhibited low susceptibility to NaCl. These findings underscore the functional and structural diversity that can be encountered among class D ␤-lactamases.

Section: Resultsmentioning

confidence: 99%

OXA-46, a New Class D β-Lactamase of Narrow Substrate Specificity Encoded by abla_VIM-1-Containing Integron from aPseudomonas aeruginosaClinical Isolate

Giuliani

Docquier

Riccio

et al. 2005

“…OXA-15 has increased ability to hydrolyze ceftazidime compared to that of OXA-2, but it also hydrolyzes cefepime and aztreonam at a lower level than OXA-2. OXA-32 is another OXA-2 derivative possessing an expanded-spectrum hydrolysis profile, identified in a ceftazidime-resistant P. aeruginosa isolate recovered from a patient originating from Guadeloupe in the French West Indies (124). The bla OXA-32 gene was integron borne and located on a 250-kb conjugative plasmid.…”

Section: Acquired Es-oxasmentioning

confidence: 99%

Diversity, Epidemiology, and Genetics of Class D β-Lactamases

Poirel

Naas

Nordmann

2010

Self Cite

545

485

Class D ␤-lactamase-mediated resistance to ␤-lactams has been increasingly reported during the last decade. Those enzymes also known as oxacillinases or OXAs are widely distributed among Gram negatives. Genes encoding class D ␤-lactamases are known to be intrinsic in many Gram-negative rods, including Acinetobacter baumannii and Pseudomonas aeruginosa, but play a minor role in natural resistance phenotypes. The OXAs (ca. 150 variants reported so far) are characterized by an important genetic diversity and a great heterogeneity in terms of ␤-lactam hydrolysis spectrum. The acquired OXAs possess either a narrow spectrum or an expanded spectrum of hydrolysis, including carbapenems in several instances. Acquired class D ␤-lactamase genes are mostly associated to class 1 integron or to insertion sequences.

“…The OXA-2 and OXA-10 ␤-lactamases exemplify the narrow-spectrum enzymes capable of producing resistance to penicillins and some early cephalosporins (4). Both enzymes, however, can extend their substrate profile to produce resistance to expanded-spectrum cephalosporins, such as ceftazidime, by accumulating one to several amino acid substitutions (5)(6)(7)(8)(9)(10)(11)(12). Class D carbapenemases, also known as carbapenem-hydrolyzing class D ␤-lactamases (CHDLs) (4), represent a further expansion of the substrate profile of class D enzymes to include carbapenem antibiotics.…”

mentioning

confidence: 99%

Class D β-Lactamases: Are They All Carbapenemases?

Antunes

Lamoureaux

Tóth

et al. 2014

131

139

Carbapenem-hydrolyzing class D ␤-lactamases (CHDLs) are enzymes of the utmost clinical importance due to their ability to produce resistance to carbapenems, the antibiotics of last resort for the treatment of various life-threatening infections. The vast majority of these enzymes have been identified in Acinetobacter spp., notably in Acinetobacter baumannii. The OXA-2 and OXA-10 enzymes predominantly occur in Pseudomonas aeruginosa and are currently classified as narrow-spectrum class D ␤-lactamases. Here we demonstrate that when OXA-2 and OXA-10 are expressed in Escherichia coli strain JM83, they produce a narrow-spectrum antibiotic resistance pattern. When the enzymes are expressed in A. baumannii ATCC 17978, however, they behave as extended-spectrum ␤-lactamases and confer resistance to carbapenem antibiotics. Kinetic studies of OXA-2 and OXA-10 with four carbapenems have demonstrated that their catalytic efficiencies with these antibiotics are in the same range as those of some recognized class D carbapenemases. These results are in disagreement with the classification of the OXA-2 and OXA-10 enzymes as narrow-spectrum ␤-lactamases, and they suggest that other class D enzymes that are currently regarded as noncarbapenemases may in fact be CHDLs.