Aminoglycoside resistance in a clinical isolate of Acinetobacter genomic species 13TU is associated with the up-regulation of its AdeABC-like efflux system
Abstract number: P795
Objectives:Acinetobacter genomic species (GS) 13TU is a member of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex. Although commonly isolated from hospitalized patients, this species, unlike A. baumannii, is usually well susceptible to antibiotics. In a Czech hospital, two isolates of a GS 13TU strain differing in their susceptibilities to aminoglycosides were obtained from the same patient. The aim of this study was to assess whether the difference is associated with the up-regulation of the GS 13TU efflux system related to the AdeABC system in A. baumannii.
Methods: The two isolates, NIPH 952 and NIPH 953, were obtained, respectively, from the sputum and gastric juice of an ICU patient. Compared to NIPH 952, NIPH 953 showed elevated MICs to aminoglycosides, in particular to gentamicin (1 versus 8 mg/l) and netilmicin (2 versus 16 mg/l). The presence of the genes encoding putative efflux components was tested by PCR using primers derived from the AdeABC genes. The ability of NIPH 952 to produce aminoglycoside-resistant variants was assessed by challenging it with 4 or 8 mg/l of gentamicin. The adeB gene was partially sequenced and its expression level was examined by real-time reverse transcription PCR (RT-PCR).
Results: PCR amplicons of expected sizes were obtained with primers targeting adeA, adeB and adeS in both NIPH 952 and NIPH 953. The sequences of the adeB-like amplicons were identical in both isolates and were 8489% identical to the known adeB sequences in A. baumannii. Variants with gentamicin MICs of more than 4 mg/l were obtained from NIPH 952 at frequencies of ~5×10-9. Two of these variants were further investigated, i.e. NIPH 952-I (gentamicin MIC 8 mg/l) and NIPH 952-IV (gentamicin MIC 24 mg/l). Compared to NIPH 952, the susceptibility patterns of NIPH 952-I, NIPH 952-IV and NIPH 953 shared elevated MICs to aminoglycosides, tetracycline, tigecycline and ciprofloxacin, whereas no changes in MICs were observed for piperacillin, cefotaxime, sulphonamides or polymyxins. Consistently, RT-PCR identified 27-fold, 214-fold and 38-fold increases in mRNA transcripts for adeB in NIPH 952-I, NIPH 952-IV and NIPH 953, respectively, as compared to NIPH 952.
Conclusion: The aminoglycoside resistance of the gastric GS 13TU isolate is likely to result from the up-regulation of its efflux system homologous to the AdeABC system in A. baumannii.
Supported by grant 310/08/1747 of the Grant Agency of the Czech Republic.
|Session name:||Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Vienna, Austria, 10 - 13 April 2010|
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