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Updated: Nov 12, 2025

Antimicrobial Synergy Testing by the Inkjet Printer-assisted Automated Checkerboard Array and the Manual Time-kill Method
Published on: April 18, 2019
Combination inhibition activity of chlorhexidine and antibiotics on multidrug-resistant Acinetobacter baumannii in
Fei Lin1, Bin Yu2, Qinghui Wang3
1Department of Pharmacy, Clinical Medical College and The First Affiliated Hospital of Chengdu Medical College, Chengdu, Sichuan, China.
Background:
Chlorhexidine is a widely used disinfectant in clinical settings and a broad-spectrum antimicrobial agent effective against aerobic and anaerobic bacteria. However, disinfectant resistant or non-susceptible bacteria, including antibiotic-resistant Acinetobacter baumannii, have been found. This study aimed to develop a new technique to prevent and control A. baumannii infection in the hospital setting.
Methods:
Chlorhexidine combined with minocycline, doxycycline, meropenem, imipenem, levofloxacin and ciprofloxacin were tested against the 30 multidrug-resistant and extremely drug-resistant A. baumannii clinical isolates. The checkerboard test was used to calculate the fractional inhibitory concentration index according to the minimum inhibitory concentration value for chlorhexidine combined with antibiotics.
Results:
The combination of chlorhexidine with minocycline, doxycycline, meropenem, or ciprofloxacin showed synergistic responses in all clinical isolates, and more than 50% of isolates showed FICI ≤0.5. However, chlorhexidine together with imipenem or levofloxacin showed indifferent responses in 10% and 3.33% clinical isolates, respectively. In all tests, combinations of chlorhexidine with each of the above six antibiotics showed synergistic and additive effects, and inhibited the clinical isolates.
Conclusions:
We concluded that, chlorhexidine combined with antibiotics could be used to control the risk of infection with A. baumannii.
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