Biochemical characteristics of a carbapenemase from an Acinetobacter baumannii isolate collected in Buenos Aires, Argentina

Abstract

Three carbapenem-resistant Acinetobacter baumannii isolates were collected at a hospital in Buenos Aires, Argentina. Isoelectric focusing revealed multiple beta-lactamases, with two of the isolates showing identical profiles. A pI 6.9 carbapenemase with a molecular weight of 30 kDa was purified from one of these two isolates. The enzyme was predominantly a penicillinase, with its highest Vmax for oxacillin but highest Vmax/Km for benzylpenicillin. First-generation cephalosporins and imipenem were weaker substrates than penicillins, and oxyimino-aminothiazolyl cephalosporins were essentially stable. Meropenem-hydrolysing activity was not detected, despite resistance. The carbapenemase was inhibited by clavulanic acid and tazobactam, but not by EDTA. These kinetics place the enzyme into functional group 2; as an oxacillinase it could be placed in sub-group 2d or, as a zinc-independent carbapenemase, in sub-group 2f.

Outbreak of Carbapenem-Resistant Acinetobacter baumannii Producing the Carbapenemase OXA-23 in a Tertiary Care Hospital of Papeete, French Polynesia

“…However, their efficacy is being increasingly compromised by the emergence of carbapenem-hydrolyzing ␤-lactamases of molecular Ambler class B (metalloenzymes) and D enzymes (oxacillinases) (1,2,3,12,17). Whereas the metalloenzymes are of IMP and VIM types, the carbapenem-hydrolyzing oxacillinases are members of three subgroups of enzymes: the OXA-23, OXA-24, and OXA-58 enzymes (2,5,9,15,16,17).…”

“…Carbapenem-resistant A. baumannii strains have been isolated in Europe, Asia, and North and South America (1,2,4,5,8,13,16). Outbreaks of OXA-23-producing A. baumannii isolates have also been reported in Spain and in Brazil (2,4,8).…”

Chromosome-Encoded Class D β-Lactamase OXA-23 in Proteus mirabilis

“…Class D ␤-lactamases include oxacillin-hydrolyzing, or OXA-type, enzymes, which are characterized by hydrolysis rates for cloxacillin and oxacillin higher than that for benzylpenicillin (9). Recently, oxacillinases OXA-23 to -27, which hydrolyze imipenem have been repeatedly associated with imipenem-resistant Acinetobacter baumannii (1,2,7,11,13).During a survey of Proteus mirabilis ␤-lactamases performed in Clermont-Ferrand, France, we observed isolates that exhibited the ␤-lactam resistance phenotype of the IRT/OXA type and produced the same non-TEM ␤-lactamase of pI 6.9 (10). In this study, we report the characterization of this enzyme and its genetic support in 10 clinical P. mirabilis isolates.…”

“…Class D ␤-lactamases include oxacillin-hydrolyzing, or OXA-type, enzymes, which are characterized by hydrolysis rates for cloxacillin and oxacillin higher than that for benzylpenicillin (9). Recently, oxacillinases OXA-23 to -27, which hydrolyze imipenem have been repeatedly associated with imipenem-resistant Acinetobacter baumannii (1,2,7,11,13).…”

Outbreak of Carbapenem-Resistant Acinetobacter baumannii Producing the OXA-23 Enzyme in Curitiba, Brazil

“…Carbapenem-resistant A. baumannii strains have been isolated in Europe, Asia, and both North and South America (11). Several of the earliest reports were from South America (1,10). Carbapenemase production, penicillin-binding protein modification, and/or porin loss have been reported as mechanisms of resistance, with carbapenemase production increasingly viewed as the major mechanism (11).…”