The carbapenem-hydrolyzing class D -lactamase OXA-253 was identified in an Acinetobacter baumannii clinical isolate belonging to sequence type 113 (ST113) in Brazil. OXA-253 shares 93.8% amino acid identity with OXA-143. The bla OXA-253 gene is located on a ca. 20-kb plasmid. The genetic environment of the bla OXA-253 gene shares the highest identity with ubiquitous GR2 group plasmids usually carrying bla OXA-24/-40 genes.A cinetobacter baumannii strains are frequently associated with nosocomial infections, and their resistance to carbapenems has risen in recent decades (1, 2). The main mechanisms of resistance to carbapenems of A. baumannii are efflux pumps, porin mutations, overexpression of the chromosomally encoded OXA-51-like -lactamase, and the biosynthesis of acquired carbapenem-hydrolyzing class D -lactamases (CHDLs) (oxacillinases) (3). To date, five main groups of CHDLs have been identified in A. baumannii, the intrinsic chromosomally encoded OXA-51-like enzyme and the acquired chromosomally encoded and plasmidencoded OXA-23-like, OXA-40-like, OXA-58-like, and OXA-143-like enzymes (3). OXA-143 was first described in 2009 from an A. baumannii strain isolated in Brazil in 2004 (2). In this study, we report an A. baumannii clinical strain producing OXA-253, a variant of OXA-143. The genetic environment of the plasmidborne bla OXA-253 gene is detailed.The clinical isolate A. baumannii 25 was recovered from a perineal swab in the intensive care unit in Minas Gerais Hospital, Brazil. MICs were determined by Etest (bioMérieux, La Balmeles-Grottes, France). Isolate 25 was resistant to all -lactams, including carbapenems, and had reduced susceptibility to cefepime according to the CLSI guidelines (4) ( Table 1). It was also resistant to fluoroquinolones (ciprofloxacin), and susceptible to aminoglycosides (gentamicin, tobramycin, amikacin, and netilmicin), and tetracycline. A modified version of the CarbaNP test (5) and the CarbAcinetoNP test (P. Nordmann, personal communication) was performed and showed a carbapenemase activity. PCR experiments, performed as previously described for screening of bla , bla , bla OXA-58 and bla OXA-143 genes (6), identified a bla OXA-143 -like gene. Further sequencing of the PCR product identified the bla OXA-253 gene (GenBank number KC479324) and showed 95% nucleotide identity with the bla OXA-143 gene. The deduced protein sequence showed 17 amino acid differences between OXA-143 and OXA-253 (93.8% identity) (Fig. 1). Those amino acid changes do not occur in the conserved residues STFK (position 70 to 73) and KSG (position 216 to 218) of class D -lactamases or in the FGN structural element (position 144 to 146) of carbapenem-hydrolyzing class D -lactamases (CHDLs) (Fig. 1).Plasmid extraction from A. baumannii 25 performed by the Kieser technique yielded two plasmids of ca. 70 and 20 kb (7). The gene encoding the OXA-253 determinant from A. baumannii 25 was transferred to Escherichia coli TOP10 by electroporation. The resulting E. coli TOP10 strain harboring the plasmid o...