Abstract

Targeting Multidrug Resistant A. Baumannii to Evaluate Anti-Biofilm and Anti-Quorum Sensing Potential of Some Compounds

Background: The continuing search for new and novel antimicrobials for their potential as anti-biofilm and anti-quorum sensing agents has turned to many plant products possessing broad-spectrum anti-microbial activities. This potential has gained importance recently because the plant secondary metabolites exhibit anti-quorum sensing activity without interfering with the growth of the organism which thus would minimize the development of multidrug resistance. A. baumannii was the test organism in this study and we used carbapenem-resistant and sensitive clinical isolates. We have evaluated the anti-biofilm and anti-quorum sensing potential of two popular plant sources, namely mango seed kernels and guava leaves. Commonly used antimicrobial food preservative ε-Poly lysine was also evaluated for its anti-quorum sensing potential. Methods: Ethanolic extracts of these plant materials and ε-Poly lysine were tested for their Minimum Inhibitory Concentration (MIC) by disc diffusion method. The antibiofilm activity of the compounds was determined using a Microtitre Plate Test (MTP) and Scanning Electron Microscopy (SEM). The compounds were also evaluated for their anti-quorum sensing activity by the MTP method. Finally, these plant extracts were partially characterized by Gas Chromatography?Mass Spectrometry (GC?MS), and the major components were identified. Results: The MICs of GLE, MSKE and ε-Poly lysine against planktonic cells of the isolates were 60 µg/mL, 40 µg/mL, and 60 µg/mL respectively. The MTP test showed a significant inhibition by the natural extracts on the biofilm formation at sub?MIC concentrations. MSKE and ε-Poly lysine were the strong biofilm inhibitors that could hinder biofilm growth by over 60%-80% in both Carbapenem-Resistant Acinetobacter Baumannii (CRAB) and CSAB isolates. GLE exhibited a moderate effect on 54.5% of CRAB and 25% of CSAB isolates respectively. These results were confirmed by SEM where the biofilm has been reduced to individual cells scattered over the matrix surface. In addition, the relative number of bacteria in the biofilm matrix was significantly less compared to the untreated samples. A. baumannii cells after exposure have lost the biofilm integrity and the cells became flat and elongated. Inhibition of the quorum sensing signal molecule AHL, in terms of blue-green complex production, by MSKE was 47% in CRAB and 82% in CSAB isolates. However, GLE extract showed 42% and 69% inhibition of AHL production in CRAB and CSAB isolates respectively. Streptomycin and εPoly lysine could inhibit the production of AHL by about 40% in CRAB and 80% in CSAB isolates. Conclusions: The present study demonstrated that MSKE, GLE ethanolic extracts, and ε-Poly lysine have strong potential as antibiofilm and anti?QS compounds which could be developed further as adjunct drugs for treating multi-drug resistant A. baumannii and for co-therapy-with-other-antibiotics-to-eliminate-development of resistance

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