OXA-72-producing Acinetobacter baumannii in Brazil: a case report

Sir, Acinetobacter baumannii is a threatening nosocomial pathogen that has been reported worldwide. Its ability to survive at different pHs, temperatures and under poor nutritional conditions makes this pathogen extremely successful. Besides its intrinsic resistance to different antimicrobial agents, A. baumannii is capable of accumulating additional mechanisms of resistance, such as β-lactamase production, altered antibiotic targets, efflux pump overexpression and porin loss. Carbapenem resistance among A. baumannii clinical isolates is frequently associated with the ISAba1-related overexpression of OXA-51, a carbapenem-hydrolysing class D β-lactamase (CHDL) that is intrinsic to this species.1 In addition, the acquisition of other CHDLs has been increasingly reported among carbapenem-resistant A. baumannii clinical isolates worldwide. These enzymes are capable of hydrolysing carbapenems, but not extended-spectrum cephalosporins.2 The acquired CHDLs reported in Acinetobacter spp. are divided into four subgroups, according to their amino acid sequence identity: OXA-23-like; OXA-24/40-like; OXA-58-like; and OXA-143-like. To date, only two CHDL clusters were identified among A. baumannii clinical isolates in Brazil: OXA-23; and the recently described OXA-143.3 Here, we describe the occurrence of OXA-72, an OXA-24-like enzyme, in an A. baumannii clinical isolate from Brazil, thus increasing the diversity of CHDL clusters reported in this country. During winter 2007, an elderly patient underwent a total hip arthroplasty due to a fracture. Ten days after the surgery, he presented with fever and dyspnoea due to a wound infection. Cefepime [2 g, intravenously (iv), twice daily] was empirically introduced. A. baumannii A30235 was isolated in a blood culture. According to disc diffusion following CLSI (M100-S19) recommendations, isolate A30235 was found to be susceptible to only ampicillin/sulbactam. The antimicrobial therapy was modified to 3 g of ampicillin/sulbactam iv every 6 h. The patient showed clinical resolution and was discharged from hospital after receiving 14 days of antimicrobial therapy. Unfortunately, the follow-up of this patient was lost. Susceptibility testing was further performed using CLSI microdilution.4 Isolate A30235 showed susceptibility to polymyxin B and colistin, reduced susceptibility to ampicillin/sulbactam, and resistance to ceftazidime, cefepime, ceftriaxone, imipenem, meropenem, ciprofloxacin and amikacin (Table 1). Antimicrobial susceptibility profile of A. baumannii A30235 clinical isolate, the recipient strain A. baumannii ATCC 19606 and the transconjugant A. baumannii ATCC 19606 carrying blaOXA-72 ND, not determined. Antimicrobial susceptibility profile of A. baumannii A30235 clinical isolate, the recipient strain A. baumannii ATCC 19606 and the transconjugant A. baumannii ATCC 19606 carrying blaOXA-72 ND, not determined. A multiplex PCR assay targeting CHDL-encoding genes was performed using previously published primers and cycling conditions.5 The presence of blaOXA-51-like and blaOXA-24/40 was confirmed by PCR. DNA sequencing identified the blaOXA-24/40 amplicon as blaOXA-72. A subsequent PCR targeting both blaOXA-72 and the insertion sequence ISAba1 yielded a negative result, indicating that blaOXA-72 expression was not driven by the promoter present in this insertion sequence element. Amplification of metallo-β-lactamase-encoding genes was not detected. Plasmid extract obtained by the Kieser method6 was used to transform electrocompetent A. baumannii ATCC 19606, as previously described.3 Selection of transformants was performed in Luria–Bertani agar supplemented with 100 mg/L ticarcillin and the presence of blaOXA-72 was confirmed by PCR. Electrophoresis of plasmids extracted from a transformant and subsequent Southern blot and hybridization with a blaOXA-72-specific probe showed that the blaOXA-72 gene was located on a plasmid of ∼86 kb. Susceptibility testing of transformants revealed increased meropenem and imipenem MICs, whereas cephalosporin MICs were identical to those for A. baumannii ATCC 19606, suggesting that other cephalosporin resistance determinants were not co-transferred (Table 1). Studies with ampicillin/sulbactam have demonstrated the efficacy of this association as an alternative treatment of infections due to carbapenem-resistant Acinetobacter spp.7 According to the CLSI criteria, the strain A30235 was classified as susceptible and intermediate to ampicillin/sulbactam by disc diffusion and broth microdilution, respectively. Since minor errors have been observed for this combination by disc diffusion, determination of the ampicillin/sulbactam MIC is required when this compound is prescribed for the treatment of serious infections, such as sepsis.8 Despite being infected by an isolate that showed reduced susceptibility to ampicillin/sulbactam, the patient had a good clinical outcome after treatment. The OXA-72 enzyme was first identified in A. baumannii from Thailand, in 2004 (accession no. AY739646). Later on, this enzyme was reported in Acinetobacter spp. clinical isolates from China, South Korea, Taiwan, Italy, Spain and France.2,9–11 In this study, we identified a plasmid-encoded OXA-72 in an A. baumannii clinical isolate from Brazil. The isolate (A30235) also showed increased resistance rates to extended-spectrum cephalosporins that are not hydrolysed by OXA-72, suggesting the presence of an additional mechanism of β-lactam resistance that was not transferable with blaOXA-72. The occurrence of blaOXA-72 located in a mobile genetic element points to the increasing diversity of CHDLs among Acinetobacter spp. clinical isolates in Brazil and its potential for spread. Consequently, it is essential that Brazilian Infection Control Committee members are aware of the emergence of OXA-72. This will allow appropriate control measures to be taken to avoid its dissemination among Brazilian hospitals, which have experienced the spread of OXA-23-producing A. baumannii.12 The study was carried out as part of our routine work. A. C. G. is a researcher from the National Council for Science and Technological Development (CNPq), Ministry of Science and Technology, Brazil (Process number: 307816/2009-5).