ZnO@Carvacrol nanoparticles effectively suppress biofilm and quorum-sensing mechanisms in MDR Acinetobacter baumannii

Abstract

Background Multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) is a serious public health concern. This is mainly due to its strong biofilm formation and quorum-sensing (QS) systems, which contribute to increased antibiotic resistance. This study aimed to evaluate the inhibitory effects of zinc oxide-carvacrol nanoparticles (ZnO@Carvacrol NPs) on biofilm formation and QS gene expression in MDR A. baumannii isolates. Methods ZnO@Carvacrol NPs were synthesized using a green technique and characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Clinical isolates of A. baumannii were identified and tested for antimicrobial susceptibility. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of carvacrol and ZnO@Carvacrol NPs were determined. Biofilm formation ability was assessed using the crystal violet microtiter assay. Minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC) were determined. The expression of biofilm- and QS-related genes, including bap, abaI, and abaR, in four clinical isolates and the ATCC BAA-747 was analyzed using qRT-PCR. Results The synthesized nanoparticles featured a ZnO wurtzite crystal core, surface functional groups associated with carvacrol, and a nanoscale agglomerated morphology (50-100 nm). ZnO@Carvacrol NPs showed a high carbon content, with signals for zinc and oxygen, thereby confirming the successful production and surface modification. ZnO@Carvacrol NPs, with MIC and MBC values of 1.6 mg/mL, demonstrated greater effectiveness in inhibiting A. baumannii than carvacrol alone (MIC = 3.2 mg/mL and MBC = 6.4 mg/mL). ZnO@Carvacrol NPs decreased biofilm biomass (MBIC = 0.2 mg/mL and MBEC = 0.4 mg/mL), whereas carvacrol showed MBIC and MBEC values of 0.8 and 1.6 mg/mL, respectively. Carvacrol reduced abaI expression by 50, while ZnO@Carvacrol decreased it by approximately 70 (P < 0.01). abaR expression decreased by 40 with carvacrol and 70 with ZnO@Carvacrol NPs (P < 0.01). The bap gene showed a 60 reduction with carvacrol and an 80 reduction with ZnO@Carvacrol NPs (P < 0.001). Conclusion The anti-biofilm and anti-QS properties of ZnO@Carvacrol NPs against MDR A. baumannii showed promise. These findings suggest that ZnO@Carvacrol NPs have the potential to serve as an adjuvant in combating antibiotic resistance in A. baumannii.