[Molecular characterization of beta-lactamase-associated resistance in Acinetobacter baumannii strains isolated from clinical samples]

Hakan Keskin, Alper Tekeli, İştar Dolapci, Duygu Öcal
Mikrobiyoloji Bülteni 2014, 48 (3): 365-76
Acinetobacter baumannii is an important cause of nosocomial infections that particularly increase the mortality and the morbidity at the intensive care units of the hospitals. The aims of this study were to evaluate the resistance genes, antibiotic susceptibility and the clonal relations among Acinetobacter strains isolated from clinical samples and to determine the resistance mechanisms related to these bacteria in our hospital. A total of 201 A.baumannii strains isolated from different clinical samples (35.3% from tracheal aspirate, 27.3% from blood, 18.4% from abscess material, 19% from other samples) of 160 inpatients evaluated at the Ibni Sina Hospital Central Bacteriology Laboratory, Ankara University School of Medicine, Turkey from April 2010 to December 2011, were included in the study. Identification of the isolates and their susceptibility testing against amikacin, ciprofloxacin, tetracycline, sulbactam/ampicillin, trimethoprim/sulfametoxazole (SXT), ceftazidime, gentamicin, imipenem, levofloxacin, meropenem, piperacillin/tazobactam, cefoperazone/sulbactam, cefepime and colistin were performed by the automated systems, namely Vitek 2 (bioMérieux, France) and BD Phoenix (Becton Dickinson, USA). The molecular mechanisms of beta-lactamase resistance and the presence of integrons were analyzed by polymerase chain reaction (PCR). Moreover, since blaPER-1 gene is of high frequency in Turkey, it was also investigated in the isolates. Pulsed-field gel electrophoresis (PFGE) was performed to examine the clonal relations between isolates. Our results indicated that multidrug resistance rate of A.baumannii was 94.5% (190/201), while 94% (189/201) of the isolates were susceptible to colistin thus making it the most potent antimicrobial agent, followed by amikacin and SXT with a susceptibility rate of 32%. Twelve colistin-resistant isolates were further investigated with the E-test method (AB Biodisk, Sweden) and found to be colistin-resistant. While the results were negative for the genes responsible from metallo-beta-lactamase production, positive results were obtained for blaOXA genes at various rates (OXA-51 100%; OXA-23 91.5%; OXA-58 7%; OXA-24 2%). PFGE results revealed four different main clones (29 isolates in genotype A, 23 in genotype B, 18 in genotype C and 7 in genotype D) in the study population. No common epidemic isolate was detected. Class 1 integrons which take part in the transfer of resistance genes were detected in 112 (55.7%) isolates. There was no statistically significant difference between the genotype distributions of class 1 integron positive strains (p> 0.05). The relationship between the presence of integron in multidrug resistant isolates and resistance to tetracyclin, SXT, imipenem, meropenem, cefoperazone/sulbactam and cefepime were found to be statistically significant (p< 0.05). Of the isolates 42 (21%) were positive for blaPER- 1 gene and all were resistant to ceftazidime. This study indicated that blaOXA genes found together with blaOXA-51 genes play an important role in carbapenem resistance of A.baumannii strains. Moreover, multidrug resistance is still an important problem in infections caused by A.baumannii and integrons play a role in the transfer of the resistance genes. In conclusion, multidrug resistant A.baumannii strains were common in our hospital and our epidemiologic data would be helpful for further investigations and in therapeutical approaches.

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