Aminoglycoside resistance and distribution of resistance genes in sporadic and outbreak strains of Acinetobacter baumannii isolated in Abu Dhabi

Abstract number: O526

Pal T., Gazawi A., Sonnevend A., Ibrahim M., Belal S.E., Al-Haj M.

Objectives: The aim was to investigate the differences in the level of resistance and the distribution of aminoglycoside resistance genes between sporadic and outbreak strains of Acinetobacter baumannii.

Methods: Sixty three non-repeat A. baumannii strains clustered into seven distinct outbreak clones by macro-restriction and genotyping were compared to 50 sporadic strains isolated in Abu Dhabi in 2008. Aminoglycoside resistance genes (aadA, aac(3)-Ia, aac(3)-Iia, aac(6')-Ih, aph(3')-VI, ant(2')-Ia, aph(3')-Ia, aac(6')-Ib, armA, strAB, rmtA, rmtB, rmtC, rmtD, npmA) were detected by PCR. Antibiotic susceptibility was tested against a wide range of drugs by disc diffusion and to ceftazidime, imipenem, meropenem, ciprofloxacin, tigecycline, colistin, gentamicin, amikacin, streptomycin, kanamycin, netilmicin, spectinomycin and tobramycin by E-test.

Results: All outbreak strains and 48% of the sporadic isolates were MDR (arbitrarily defined as resistance to carbapenems and at least to further two non-b lactam classes of drugs). The MIC values of different aminoglycosides to different groups of strains are shown in Table 1. The most frequent aminoglycoside resistance gene was armA among both outbreak and sporadic isolates (61.9% and 52.0%, respectively) followed by strAB (57.1% among outbreak strains) and by aadA and aph(3')-VI (38.0% each among sporadic isolates). The most common combination of aminoglycoside resistance genes carried by members of the two largest outbreak clones were: armA, strAB (with or without aac(3)-Iia) (Clone D, N = 14) with high level of resistance to all aminoglycosides and aph(3')-VI, ant(2')-Ia (with or without armA) (Clone F, N = 19) showing high level of resistance to amikacin, gentamicin and kanamycin with varying levels to other drugs.

Conclusion: Aminoglycoside resistance is wide-spread among local outbreak isolates but also common among sporadic strains. In this latter group it is also strongly linked to resistance to other antibiotic classes, i.e. to multi-drug resistance. Particularly alarming is the wide-spread distribution of armA, often localized on plasmids and spreading rapidly in other parts of the world. Close monitoring of resistance clones and resistance genes are needed to reveal the dynamics of rapidly increasing aminoglycoside resistance in A. baumannii.

Session Details

Date: 07/05/2011
Time: 00:00-00:00
Session name: Abstracts of 21st ECCMID / 27th ICC
Location: Milan, Italy, 7 - 10 May 2011
Presentation type:
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