Evaluation of antimicrobial susceptibility tests for Acinetobacter and Pseudomonas species using disks containing a
Shoichiro Endo1,2, Tatsuya Tada1, Satoshi Oshiro1
1Department of Microbiology, Juntendo University School of Medicine, Tokyo, Japan.
Abstract:
The emergence and dissemination of carbapenem-resistant species of Acinetobacter and Pseudomonas have become a serious health concern. Routine antimicrobial disk susceptibility tests in clinical laboratories cannot distinguish between isolates that are highly carbapenem-resistant and those that are moderately carbapenem-resistant. The present study describes antimicrobial susceptibility tests using disks containing high doses (1000 μg) of meropenem. The diameters of inhibition zones were significantly negatively correlated with the MICs of Pseudomonas and Acinetobacter species for meropenem (R2: 0.93 and 0.91, respectively) and imipenem (R2: 0.75 and 0.84, respectively). Double disk synergy tests using clavulanic acid or sodium mercaptoacetate can detect ESBL or MBL producers. Susceptibility tests using disks containing high doses of meropenem can easily detect highly carbapenem-resistant isolates in a quantitative manner. These disks may be useful in bacteriological laboratories because of their technical ease, stability, and relatively low cost.
Insights
High-dose meropenem disks accurately differentiate highly carbapenem-resistant Acinetobacter and Pseudomonas, aiding clinical labs. This cost-effective method offers technical ease for detecting resistant bacterial isolates.
Area of Science:
- Clinical microbiology
- Antimicrobial resistance
- Bacterial genetics
Background:
- Carbapenem-resistant Acinetobacter and Pseudomonas pose significant global health threats.
- Current antimicrobial susceptibility testing methods lack the precision to distinguish high from moderate carbapenem resistance.
- Accurate identification of resistance levels is crucial for effective treatment strategies.
Purpose of the Study:
- To evaluate the efficacy of high-dose (1000 μg) meropenem disks for differentiating highly carbapenem-resistant Acinetobacter and Pseudomonas isolates.
- To establish a correlation between inhibition zone diameters and minimum inhibitory concentrations (MICs) using this novel disk diffusion method.
- To assess the utility of this method as a practical tool for clinical laboratories.
Main Methods:
- Antimicrobial susceptibility testing was performed using disks containing 1000 μg of meropenem.
- Correlation analysis was conducted between inhibition zone diameters and meropenem/imipenem MICs for Acinetobacter and Pseudomonas species.
- Double disk synergy tests with clavulanic acid or sodium mercaptoacetate were employed to detect specific resistance mechanisms (ESBL, MBL).
Main Results:
- A significant negative correlation was observed between inhibition zone diameters and MICs for meropenem (R²: 0.93 for Pseudomonas, 0.91 for Acinetobacter) and imipenem (R²: 0.75 for Pseudomonas, 0.84 for Acinetobacter).
- High-dose meropenem disks effectively distinguished highly carbapenem-resistant isolates in a quantitative manner.
- Double disk synergy tests successfully identified ESBL and MBL producers.
Conclusions:
- High-dose meropenem disk susceptibility tests provide a reliable and quantitative method for detecting highly carbapenem-resistant Acinetobacter and Pseudomonas.
- This technique offers a technically simple, stable, and cost-effective alternative for bacteriological laboratories.
- The method facilitates accurate differentiation of resistance levels, supporting improved patient management and infection control.
