Investigating the in vitro synergistic activities of several antibiotic combinationsagainst carbapenem-resistant Acinetobacter baumannii isolates.

BACKGROUND/AIM: Acinetobacter baumannii (A. baumannii) is one of the most common healthcare-associated infectious agents worldwide. The aim of this study was to investigate the in vitro synergistic activities of several antibiotic combinations against carbapenem-resistant (CR) A. baumannii isolates. MATERIALS AND METHODS: Eighteen CR A. baumannii strains were isolated from the patients who were hospitalized in the intensive care unit between June 2012 and August 2012. The in vitro effects of single and binary combinations of meropenem (MEM), colistin (CST), tigecycline (TGC), and sulbactam (SUL) on these isolates were determined using the Epsilometer test (E-test) method. RESULTS: All 18 isolates were resistant to MEM and SUL and susceptible to CST. TGC was detected as susceptible in two of the isolates and intermediate susceptibility results were observed in the remaining isolates. With MEM-CST and MEM-TGC combinations, synergism was determined against all isolates. The synergistic and/or additive effect ratios were detected in MEM-SUL, CST-SUL, TGC-SUL, and CST-TGC combinations as 16.7%, 38.9%, 16.7%, and 5.6%, respectively. CONCLUSION: Among the tested antimicrobial combinations, the in vitro combination of MEM with TGC or CST was most effective against the CR A. baumannii strains.

[Investigation of oxacillinase genes in nosocomial multidrug-resistant Acinetobacter baumannii isolates by multiplex PCR and evaluation of their clonal relationship with Rep-PCR]. / Nozokomiyal çok ilaca dirençli Acinetobacter baumannii izolatlarinda oksasilinaz genlerinin multipleks PCR ile arastirilmasi ve klonal iliskilerinin Rep-PCR ile degerlendirilmesi.

Acinetobacter baumannii is a major nosocomial pathogen which can cause infections with high morbidity and mortality in hospitalized patients. In recent years A.baumannii has become a serious clinical problem because of the development of resistance to many antibiotics, and especially to carbapenems. The aims of this study were to investigate the oxacillinase genes responsible for carbapenem resistance in multidrug resistant (MDR) A.baumannii strains and to evaluate the clonal relationship between these strains. A total of 62 MDR A.baumannii strains isolated from various clinical specimens (24 tracheal aspirate, 14 wound, 10 blood, 7 urine, 2 abscess, 2 sputum, 2 catheter tip, 1 pleural fluid) of hospitalized patients in intensive care units (n= 42) and other inpatient clinics (n= 20) between February-March 2012, were included in the study. Identification and antibiotic susceptibility of A.baumannii isolates were performed by Vitek-2 automated system (bioMérieux, France), and the identified bacteria were confirmed by Maldi Biotyper (Bruker Daltonics, Germany) system. Imipenem, meropenem, colistin and tigecycline were additionally tested by E-test strips (bioMérieux, France). The presence of carbapenemase-producing OXA genes (blaOXA-23-like, blaOXA-40-like, blaOXA-51-like and blaOXA-58-like) were detected by multiplex PCR (hyplex® CarbOxaID test system, Amplex Diagnostics, Germany) and the clonal relationship between isolates were investigated by rep-PCR method (DiversiLab, bioMérieux, France). In our study, all isolates were found resistant to ampicillin-sulbactam, piperacillin, piperacillin-tazobactam, ceftazidime, cefepime, imipenem, meropenem, ciprofloxacin, levofloxacin and tetracycline, while the resistance rates for amikacin, gentamicin, trimethoprim-sulfamethoxazole, netilmicin and tigecycline were 88.7%, 88.7%, 82.3%, 43.5% and 27.4%, respectively. All A.baumannii isolates were susceptible to colistin. All of the strains were positive for blaOXA-23-like and blaOXA-51-like genes, while blaOXA-40-like and blaOXA-58-like genes were not detected in any of them. Simultaneous cultures from environmental samples collected from inpatient clinics in which MDR A.baumannii strains isolated were negative in terms of A.baumannii growth. In evaluation of clonal relationship between isolates, 48 strains (77.4%) showed greater than 95% similarity and formed a big cluster, named Cluster A. The remaining 14 isolates formed 3 small clusters (each had 2 isolates), named Cluster B, C and D, showing greater than 95% similarity. Majority of isolates (58.3%) in Cluster A were from patients in the surgical intensive care unit, and the first isolate from this cluster was also from a patient in the same unit. In our opinion, isolates from Cluster A may have spread to other clinics from surgical intensive care unit through transferred patients or medical and non-medical devices and equipment. Nosocomial MDR A.baumannii isolates in our hospital are highly resistant to antibiotics and all harboured blaOXA-23-like genes. The rep-PCR analysis of these isolates indicated that a large portion of A.baumannii strains were clonally closely related, and they probably from the same source and common ancestor, and separated shortly from each other. This data emphasizes that the choices of treatment are quite limited for inpatients, and the need for improvement of the infection control measures in our hospital.