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Antimicrobial Synergy Testing by the Inkjet Printer-assisted Automated Checkerboard Array and the Manual Time-kill Method
Published on: April 18, 2019
[In vitro antimicrobial synergy against imipenem-resistant Acinetobacter baumannii]
Heungsup Sung1, Soo Jin Choi, Soojin Yoo
1Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea.
Background:
Most imipenem-resistant Acinetobacter baumannii (IRAB) isolates are multiresistant, leaving few options for an effective antimicrobial therapy. We purposed to select possible candidates for the combinations of antimicrobials that are synergistic in vitro for inhibitory or bactericidal activities against IRAB and evaluate the usefulness of double disk synergy test (DDS) in predicting synergistic bactericidal activity.
Methods:
Fifty-five IRAB isolates recovered from patients during the period from August 1999 to November 2000 were tested for susceptibilities to amikacin, gentamicin, tobramycin, piperacillin, piperacillin/tazobactam, cefotaxime, cefepime, cefoperazone/sulbactam (C/S), imipenem, meropenem, ciprofloxacin, levofloxacin, trimethoprim/sulfamethoxazole, chloramphenicol, minocycline, and colistin by the Clinical and Laboratory Standard Institute agar dilution method. Three isolates showing different susceptibility profiles were tested for antimicrobial synergy by DDS and then by timekill study (TKS) using DDS-positive combinations.
Results:
Colistin, C/S, and minocycline were active in 50 (90.9%), 50, and 44 (80.0%) isolates, respectively, and all the other drugs were active in less than 20% of isolates. Minocycline-imipenem, minocycline-C/S, minocycline-amikacin, imipenem-tobramycin, C/S-amikacin, and C/S-tobramycin combinations showed synergistic inhibitory or bactericidal activity by TKS when the same combinations were synergistic in DDS; however, C/S-imipenem was found synergistic on DDS, but not by TKS.
Conclusions:
Colistin, C/S, and minocycline were relatively active against IRAB. DDS might help predict the synergistic antimicrobial effect of TKS if one of the combinations was susceptible.
Insights
Colistin, cefoperazone/sulbactam (C/S), and minocycline show activity against imipenem-resistant Acinetobacter baumannii (IRAB). The double disk synergy test (DDS) can help predict synergistic antimicrobial combinations for treating IRAB infections.
Area of Science:
- Medical Microbiology
- Antimicrobial Resistance
- Infectious Diseases
Background:
- Imipenem-resistant Acinetobacter baumannii (IRAB) presents a significant challenge due to multidrug resistance.
- Limited effective antimicrobial options exist for treating IRAB infections.
Purpose of the Study:
- To identify potential synergistic antimicrobial combinations against IRAB.
- To evaluate the double disk synergy test (DDS) for predicting synergistic bactericidal activity.
Main Methods:
- Susceptibility testing of 55 IRAB isolates against various antibiotics using the Clinical and Laboratory Standard Institute agar dilution method.
- Antimicrobial synergy assessment using DDS followed by time-kill studies (TKS) for DDS-positive combinations.
Main Results:
- Colistin (90.9%), cefoperazone/sulbactam (C/S) (80.0%), and minocycline (80.0%) demonstrated activity against IRAB isolates.
- Synergistic inhibitory or bactericidal activity was observed with minocycline-imipenem, minocycline-C/S, minocycline-amikacin, imipenem-tobramycin, C/S-amikacin, and C/S-tobramycin combinations in TKS when also synergistic in DDS.
- Cefoperazone/sulbactam (C/S) and imipenem combination showed synergy in DDS but not in TKS.
Conclusions:
- Colistin, C/S, and minocycline are relatively active agents against IRAB.
- DDS can be a useful predictor of synergistic antimicrobial effects observed in TKS for IRAB treatment.
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