Potential of Cannabidiol (CBD) to overcome extensively drug-resistant Acinetobacter baumannii

Abstract

Extensively drug-resistant (XDR) Acinetobacter baumannii poses a serious clinical challenge due to its resistance to nearly all available antibiotics, including carbapenems and colistin. Cannabidiol (CBD), a non-psychoactive phytochemical from Cannabis sativa L., has recently shown promising antimicrobial activity. This study evaluates the antibacterial and anti-biofilm effects of CBD against XDR A. baumannii isolates and explores its mechanism of action and potential as an adjunct therapeutic agent. Twenty-six A. baumannii isolates collected from ICU medical devices were identified using MALDI-TOF/MS. Antimicrobial susceptibility was assessed by disk diffusion and broth microdilution to determine MICs and MBCs for CBD and standard antibiotics. Synergistic effects were evaluated via checkerboard assays and FICI values. Biofilm inhibition and eradication were assessed using crystal violet and MTT assays. Time-kill studies, membrane integrity assays (DNA/protein leakage, NPN uptake, membrane depolarization), and scanning electron microscopy (SEM) were employed to investigate bactericidal kinetics and membrane-disruptive mechanisms. CBD exhibited activity against antimicrobial resistance isolates (MIC: 3.9 to > 500 µg/mL). Remarkably, CBD synergized with gentamicin, meropenem, and colistin, reducing their effective concentrations by up to 1,000-fold. Combination therapy significantly inhibited and eradicated biofilms. Time-kill assays demonstrated rapid, concentration-dependent killing, with complete bacterial clearance at 4× MIC within 2 h. Mechanistic assays and SEM confirmed that CBD induces extensive membrane damage. These findings highlight CBD's potential as an effective adjunct to conventional antibiotics for treating XDR A. baumannii infections, offering a novel strategy to counteract antimicrobial resistance.

Keywords: Acinetobacter baumannii; Antimicrobial resistant; Cannabidiol; Extensively drug resistant; Synergistic.

Fig. 1

Effect of cannabidiol (CBD) and its combination with gentamicin (CN), meropenem (MEM), and colistin (CO) on biofilm formation. The antimicrobial resistance A. baumannii isolate A29 was exposed to CBD alone (at 1×, 2×, and 4× MIC), gentamicin, meropenem, and colistin alone, or the CBD–antibiotic combinations for biofilm formation assays, as well as for assessing preformed biofilm biomass and viability. Biofilm formation (A) and preformed biofilm (B) were evaluated using crystal violet staining, while the viability of preformed biofilm (C) was assessed using the MTT assay. *p < 0.05, ***p < 0.001

Fig. 2

The effect of CBD on the XDR A. baumannii isolate A29 was assessed using time-kill kinetics. Isolate A29 was exposed to CBD alone at 1×, 2×, 4×, and 8× MIC for 1, 2, 4, 8, 16, and 24 h (A) or in combination with gentamicin (B), meropenem (C), and colistin (D). Viable cells were counted and expressed on a log scale. Dashed bars indicate the bactericidal threshold

Fig. 3

Effect of CBD on outer membrane integrity. The A. baumannii isolate A29 was exposed to CBD at concentrations of 1×, 2×, and 4× MIC for 1 h at 37 °C. DNA (A) and protein (B) leakage levels were measured. The relative fluorescence intensity (RFI) of NPN (C) and Rh123 (D) was also assessed. Triton X-100 (0.1%) served as the positive control (TX). ***p < 0.001

Fig. 4

Effect of CBD on bacterial cell morphology. A. baumannii isolate A29 was treated with 250 µg/mL of CBD for 2 h at 37 °C. Scanning electron microscopy (SEM) images at ×15,000 and ×25,000 magnifications are shown: (a) represents the untreated control, while (b) represents the CBD-treated cells. Cell damage is indicated by arrows

Fig. 5

Cytotoxic effects of CBD in normal human epithelial (HEK293) cells. HEK293 cells were treated with CBD at concentrations ranging from 0.5 to 5 µg/mL for 24, 48, and 72 h. Cell viability was assessed using the MTT assay. ***p < 0.001