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Identification of a novel blaOXA-51 variant, blaOXA-92, from a clinical isolate of Acinetobacter baumannii

2006; Elsevier BV; Volume: 13; Issue: 3 Linguagem: Inglês

10.1111/j.1469-0691.2006.01598.x

1469-0691

Athanassios Tsakris, A. Ikonomidis, Nicholas Spanakis, Spyros Pournaras, K Bethimouti,

Vibrio bacteria research studies

Recent articles in CMI have described a novel subgroup of OXA-type β-lactamases that appears to be intrinsic in Acinetobacter baumannii [1Brown S Young HK Amyes SGB Characterisation of OXA‐51, a novel class D carbapenemase found in genetically unrelated clinical strains of Acinetobacter baumannii from Argentina.Clin Microbiol Infect. 2005; 11: 15-23Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar, 2Brown S Amyes SGB The sequences of seven class D β‐lactamases isolated from carbapenem‐resistant Acinetobacter baumannii from four continents.Clin Microbiol Infect. 2005; 11: 326-329Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, 3Poirel L Nordmann P Carbapenem resistance in Acinetobacter baumannii: mechanisms and epidemiology.Clin Microbiol Infect. 2006; 12: 826-836Crossref PubMed Scopus (744) Google Scholar]. These oxacillinases are chromosomally-encoded and exhibit very poor hydrolytic activities against carbapenems unless insertion sequence ISAba1 is located upstream of the blaOXA-51-like gene [3Poirel L Nordmann P Carbapenem resistance in Acinetobacter baumannii: mechanisms and epidemiology.Clin Microbiol Infect. 2006; 12: 826-836Crossref PubMed Scopus (744) Google Scholar, 4Turton JF Ward ME Woodford N et al.The role of ISAba1 in expression of OXA carbapenemase genes in Acinetobacter baumannii.FEMS Microbiol Lett. 2006; 258: 72-77Crossref PubMed Scopus (543) Google Scholar]. Approximately 20 variants of the prototype enzyme, OXA-51, have now been described. We describe the identification of a further novel OXA-51 variant in A. baumannii that has been designated OXA-92. An isolate of A. baumannii was recovered from the blood culture of a patient hospitalised in a Greek intensive care unit. MICs of imipenem and meropenem were determined by the agar dilution method, and the isolate was screened for blaOXA-51-like genes using the external primers OXA-69A and OXA-69B [5Héritier C Poirel L Fournier P‐E Claverie J‐M Raoult D Nordmann P Characterisation of the naturally occurring oxacillinase of Acinetobacter baumannii.Antimicrob Agents Chemother. 2005; 49: 4174-4179Crossref PubMed Scopus (229) Google Scholar]. These primers amplify a 975-bp product that includes the whole coding sequence of the gene, which allows the different alleles to be discriminated by sequence analysis. PCR was also performed using primers specific for other carbapenemase-encoding genes (blaIMP, blaVIM, blaSIM, blaOXA-23-like, blaOXA-24-like and blaOXA-58) [6Pournaras S Markogiannakis A Ikonomidis A et al.Outbreak of multiple clones of imipenem‐resistant Acinetobacter baumannii isolates expressing OXA‐58 carbapenemase in an intensive care unit.J Antimicrob Chemotherapy. 2006; 57: 557-5561Crossref PubMed Scopus (131) Google Scholar, 7Lee K Yum JH Yong D et al.Novel acquired metallo‐β‐lactamase gene, blaSIM‐1, in a class 1 integron from Acinetobacter baumannii clinical isolates from Korea.Antimicrob Agents Chemother. 2005; 49: 4485-4491Crossref PubMed Scopus (275) Google Scholar]. Insertion sequence ISAba1 was detected by PCR as described previously [4Turton JF Ward ME Woodford N et al.The role of ISAba1 in expression of OXA carbapenemase genes in Acinetobacter baumannii.FEMS Microbiol Lett. 2006; 258: 72-77Crossref PubMed Scopus (543) Google Scholar], and the genetic element carrying the blaOXA-51-like gene was investigated by PCR mapping using ISAba1 forward and blaOXA-51-like reverse primers. The imipenem and meropenem MICs for the isolate were 64 mg/L and 8 mg/L, respectively. The strain was multidrug-resistant, exhibiting resistance to all other antimicrobial agents except colistin. PCR screening was positive for blaOXA-51-like and blaOXA-58 genes, but negative for blaIMP, blaVIM, blaSIM, blaOXA-23-like and blaOXA-24-like genes. Sequencing of the blaOXA-51-like amplicon revealed a novel variant that had a G701C transversion compared with the blaOXA-69 gene sequence. This transversion resulted in a tryptophan to serine amino-acid substitution at position 234 (numbering according to OXA-69). The mutation was outside the standard S-T-F-K, S-X-I, Y-G-N and K-S-G oxacillinase motifs, and possibly did not affect the hydrolytic activity of the oxacillinase. Sequence alignment of the new allele revealed 99% nucleotide and amino-acid identity with blaOXA-69, 98% with blaOXA-65 and blaOXA-66, and 97% with the prototype blaOXA-51 gene. This novel blaOXA-51 variant was designated blaOXA-92 (GenBank accession number DQ335566). The PCR for ISAba1 was positive, but the PCR using the ISAba1 forward and blaOXA-51-like reverse primers failed to yield an amplicon. The subgroup of class D carbapenemases comprising the OXA-51 variants was first detected in distinct clones of A. baumannii from Argentina [1Brown S Young HK Amyes SGB Characterisation of OXA‐51, a novel class D carbapenemase found in genetically unrelated clinical strains of Acinetobacter baumannii from Argentina.Clin Microbiol Infect. 2005; 11: 15-23Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar]. The number of alleles identified in this subgroup seems to be increasing rapidly, so that, to date, c. 20 β-lactamases belonging to this subgroup have been identified among A. baumannii isolates from Argentina, South Africa, Hong Kong, Singapore and Europe [2Brown S Amyes SGB The sequences of seven class D β‐lactamases isolated from carbapenem‐resistant Acinetobacter baumannii from four continents.Clin Microbiol Infect. 2005; 11: 326-329Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, 4Turton JF Ward ME Woodford N et al.The role of ISAba1 in expression of OXA carbapenemase genes in Acinetobacter baumannii.FEMS Microbiol Lett. 2006; 258: 72-77Crossref PubMed Scopus (543) Google Scholar, 5Héritier C Poirel L Fournier P‐E Claverie J‐M Raoult D Nordmann P Characterisation of the naturally occurring oxacillinase of Acinetobacter baumannii.Antimicrob Agents Chemother. 2005; 49: 4174-4179Crossref PubMed Scopus (229) Google Scholar, 8Vahaboglu H Budak F Kasap M et al.High prevalence of OXA‐51‐type class D β‐lactamases among ceftazidime‐resistant clinical isolates of Acinetobacter spp.: co‐existence with OXA‐58 in multiple centres.J Antimicrob Chemother. 2006; 58: 537-542Crossref PubMed Scopus (63) Google Scholar, 9Woodford N Ellington MJ Coelho JM et al.Multiplex PCR for genes encoding prevalent OXA carbapenemases in Acinetobacter spp.Int J Antimicrob Agents. 2006; 27: 351-353Abstract Full Text Full Text PDF PubMed Scopus (792) Google Scholar]. The members of the cluster diverge by one to 15 amino-acid modifications, and these intrinsic enzymes seem to represent a diverse collection of β-lactamases in A. baumannii which, unlike other class D carbapenemases, do not possess the tyrosine to phenylalanine substitution in the conserved Y-G-N motif of the class D protein [10Brown S Amyes S OXA β‐lactamases in Acinetobacter: the story so far.J Antimicrob Chemother. 2006; 57: 1-3Crossref PubMed Scopus (162) Google Scholar]. In the new blaOXA-92 allele, ISAba1 was not found upstream of the blaOXA-92 structural gene, implying that other mechanisms were most likely associated with carbapenem resistance in this isolate. The blaOXA-92 gene differed from the original blaOXA-69 gene by a single amino-acid mutation, and these two genes should be regarded as alleles derived from a common ancestor. This observation is further supported by the fact that the original blaOXA-69 gene and the closely related blaOXA-66 gene have been detected previously in our hospitals [6Pournaras S Markogiannakis A Ikonomidis A et al.Outbreak of multiple clones of imipenem‐resistant Acinetobacter baumannii isolates expressing OXA‐58 carbapenemase in an intensive care unit.J Antimicrob Chemotherapy. 2006; 57: 557-5561Crossref PubMed Scopus (131) Google Scholar, 11Tsakris A Ikonomidis A Pournaras S et al.VIM‐1 metallo‐β‐lactamase in Acinetobacter baumannii.Emerg Infect Dis. 2006; 12: 981-983Crossref PubMed Scopus (71) Google Scholar]. Surveillance studies are suggested in order to monitor the dissemination of A. baumannii strains carrying blaOXA-51/69 derivatives in hospitals in our region and to determine their association with promoter sequences.