Glabridin Functions as a Quorum Sensing Inhibitor to Inhibit Biofilm Formation and Swarming Motility of Multidrug-Resistant Acinetobacter baumannii

Abstract

Objective

Acinetobacter baumannii is a hazardous bacterium that causes hospital-acquired nosocomial infections, and the advent of multidrug-resistant A. baumannii (MDR-AB) strains is concerning. Novel antibacterial therapeutic strategies must be developed. The biological effects of glabridin on MDR-AB were investigated in this study.

Methods

The minimum inhibitory concentrations (MICs) of glabridin against eight clinical MDR-AB strains were determined using the broth microdilution technique. Crystal violet staining was used to assess biofilm development, which has significant contribution to bacterial resistance. Swarming motility was measured according to surface growth zone of MDR-AB on LB agar medium. qRT-PCR was used to evaluate the expression of quorum sensing genes abaI and abaR. Glabridin and routinely used therapeutic antimicrobial agents were tested for synergistic action using the checkerboard method.

Results

According to our findings, glabridin suppressed MDR-AB growth at high doses (512–1024 μg/mL). The 1/4 MIC of glabridin significantly decreased MDR-AB biofilm formation by 19.98% (P < 0.05), inhibited MDR-AB motility by 44.27% (P < 0.05), whereas the 1/2 MIC of glabridin dramatically reduced MDR-AB biofilm development by 27.43% (P < 0.01), suppressed MDR-AB motility by 50.64% (P < 0.05). Mechanistically, glabridin substantially downregulated the expression of quorum sensing-related genes abaI and abaR by up to 39.12% (P < 0.001) and 25.19% (P < 0.01), respectively. However, no synergistic effect between glabridin and antibacterial drugs was found.

Conclusion

Glabridin might be a quorum sensing inhibitor that inhibits MDR-AB biofilm development and swarming motility.

Keywords:

• Acinetobacter baumannii
• multidrug-resistance
• glabridin
• quorum sensing

Data Sharing Statement

All data generated or analyzed during this study are fully incorporated within this article. For any additional inquiries, please feel free to contact the corresponding author.

Ethics Approval and Consent to Participate

The Ethics Committee of the First Affiliated Hospital of Wenzhou Medical University approved this study (Issuing No. 2022R048). The Ethics Committee waived the need for informed consent because it was an observational study primarily focused on microorganisms and without any treatments on patients, and all personal information of patients was correctly anonymised and de-identified during data collection. All experimental techniques in this work properly followed relevant laws, institutional guidelines, and the ethical principles specified in the Helsinki Declaration.

Acknowledgments

We sincerely appreciate the contributions of the reviewers to this manuscript.

Disclosure

The authors declare that they have no competing interests in this work.

Additional information

Funding

This work was funded by the Major Projects of Wenzhou Science and Technology Bureau (ZY2019011), the Natural Science Foundation of Zhejiang Province (LY20H200004), and Key Laboratory of Clinical Laboratory Diagnosis and Translational Research of Zhejiang Province (2022E10022).