Polyhydroxybutyrate nanoparticle improving the sensitivity of Pseudomonas aeruginosa to ceftriaxone and reducing the biofilm formation in vitro.

Background: Polyhydroxybutyrate nanoparticles (PHB-NPs) represent a promising strategy for addressing the growing threat of bacterial resistance to antibiotics - a major concern in global public health. Despite their potential, there is a noticeable gap in the current literature regarding their ability to enhance the efficacy of existing antibiotic therapies.

Objectives: This study investigates the synergistic effect of PHB-NPs in enhancing the antibacterial activity of ceftriaxone (CRO) against Pseudomonas aeruginosa, with a particular focus on mitigating key virulence factors such as biofilm formation and adhesion.

Material and methods: Polyhydroxybutyrate nanoparticles were synthesized using the pH gradient and sonication method. The antibacterial activity of PHB-NPs, CRO and the combined formulation (PHB-NP-CRO) was assessed using minimum inhibitory concentration (MIC) testing and the well diffusion method. Additionally, the effects of these formulations on P. aeruginosa biofilm formation on an abiotic surface (polystyrene) and bacterial adhesion to human oral mucosal epithelial cells (OMECs) were evaluated.

Results: The diameters of the prepared PHB-NPs ranged from 15 nm to 34 nm, with an average size of 28.2 ±6.3 nm. All P. aeruginosa isolates were capable of biofilm production. A negative correlation was observed between the diameter of the CRO inhibition zones and the extent of biofilm formation among the 20 isolates. The MICs for PHB, PHB-NPs, CRO, and the combined formulation (PHB-NP-CRO) were 2,000, 1,000, 250, and 62.5 μg/mL, respectively. Sub-MIC concentrations (as low as 1/32 MIC) of both CRO and PHB-NP-CRO exhibited significant inhibitory effects on biofilm formation and bacterial adhesion to human OMECs (p < 0.050).

Conclusions: The combination of PHB-NPs with CRO significantly enhances the antibacterial activity of CRO against P. aeruginosa. Moreover, sub-inhibitory concentrations (sub-MICs) of both PHB-NP-CRO and CRO alone effectively reduce the bacterium's ability to form biofilms and adhere to biotic surfaces.