DETECTION OF SYNERGISTIC ANTIMICROBIAL ACTIVITIES BETWEEN DORIPENEM, TIGECYCLI- NE AND COLISTIN AGAINST MULTI-DRUG-RESISTANT ACINETOBACTER BAUMANNII STRAINS OBTAINED FROM PATIENTS IN INTENSIVE CARE UNITS

LASER ŞANAL¹, NEZIHA YILMAZ², SÜHA ŞEN³, SALIH CESUR⁴

¹Yüksekİhtisas Training and Research Hospital, Microbiology Laboratory, Ankara, Turkey - ²NezihaYilmaz, Bozok University, Microbiology Department, Yozgat, Turkey - ³Yüksek İhtisas Training and Research Hospital, Infectious Diseases Department, Ankara, Turkey - ⁴Ankara Training and Research Hospital, Infectious Diseases Department, Ankara, Turkey

Introduction: Acinetobacter baumannii (A. baumannii) is an opportunistic pathogen leading to nosocomial epidemics and multidrugresistant (MDR) isolates are making the treatment of these infections more complicated. Combinations of antibiotics acting by different mechanisms are used for the treatment of MDR bacterial infections. In this study we evaluated the minimum inhi- bitory concentrations (MICs) of colistin (CO), doripenem (DOR), tigecycline (TIG) alone and in vitro synergistic activity of CO- DOR, CO-TIG and DOR-TIG combinations against MDR A. baumannii strains isolated from patients in intensive care units (ICUs).

Materials and methods: Thirty A. baumannii strains isolated from various clinical specimens of patients in ICUs were inclu- ded in the study. The epsilometer test (E-test) method was used for determining the synergistic activity of different antibiotic combinations. Synergistic, additive, indifferent and antagonist effects of A. baumannii strains were evaluated by Fractional Inhibitory Concentration (FIC) index .

Results: Of the 30 MDR A. baumannii strains tested, 90% were susceptible to TIG, 93.3% to CO and 50% to DOR. CO-DOR, CO-TIG and DOR-TIG combinations were found to have synergistic or additive effects against 3 (9.9%), 5 (16.6%) and 4 strains (13.3%), respectively. The synergistic or additive effect of DOR-TIG combination was 19.9% for DOR resistant strains and 6.6% for DOR susceptible strains. The synergistic or additive effect of CO-DOR combination was 19.9% for DOR resistant strains and 0% for DOR susceptible strains.

Conclusion: Among the tested antimicrobial combinations, the combination of CO with TIG was most effective against MDR A. baumannii strains isolated from patients in ICUs. The synergistic or additive effects both for CO-DOR and DOR-TIG combina- tions were higher in DOR resistant strains. This study suggested that combination therapy with DOR for treating MDR A. baumannii infections should be used especially in DOR resistant strains.