Comparative Evaluation of In-vitro Synergy Testing Methods in Carbapenem-Resistant Acinetobacter Species

Objective: There is an increasing incidence of Acinetobacter species causing serious hospital acquired infections such as blood stream infections (BSI), catheter associated urinary tract infections (CAUTI) and lower respiratory tract infections(LRTI) with high mortality rate of 30-75% in patients having long hospital stay especially in critical care units (CCUs). During the past decade, multi drug resistant Acinetobacter isolates have presented a real challenge to clinicians and are posing difficulties in treatment. Carbapenem-resistant Acinetobacter species particularly A. baumannii , represent a growing public health concern, since they often confer resistance to other critically important antimicrobials. Methodology: In the present study, various antibiotic combinations such as colistin + meropenem, imipenem + tigecycline, polymyxin B + azithromycin and doripenem + sulbactam are used for MDR Acinetobacter infections and tested for in-vitro combination test by Epsilometric test and Broth Micro dilution and confirmation done by time kill assay. Results: We found synergistic results with all three methods used in study with three combinations significantly (p<0.05) but with one combination i.e. doripenem+sulbactam, synergy found only with Etest not with MCB and time kill assay (p~0.069). Conclusions: We have also observed and compared outcome of the patients with respect to the treatment received during hospital stay, but we did not found significant difference between two groups, (two drug regimen & three drug regimen) regarding their mortality.  J Microbiol Infect Dis 2019; 9(1): 23-33.