Antibiofilm Activity and Synergistic Effects of Thymol-Loaded Poly (Lactic-Co-Glycolic Acid) Nanoparticles with Amikacin against Four Salmonella enterica Serovars

Abstract

Background. Salmonella species are frequently linked to biofilm-associated infections. Biofilm formation intensively reduces the efficacy of antibiotics and the host immune system. Therefore, new therapeutic strategies are needed. Thymol, the main monoterpene phenol found in Thymus vulgaris, has been shown to possess potent antibiofilm activity. Our previous findings showed that thymol enhanced the antibiofilm activity of aminoglycosides against Salmonella enterica serovars. However, the clinical potential of thymol has not yet been realized due to its low aqueous solubility and high volatility. Nano-based drug delivery systems have emerged as a novel strategy to resolve these problems. This study aimed to investigate the antibiofilm activity of thymol-loaded poly (lactic-co-glycolic acid) nanoparticles (TH-NPs) and their synergism when used in combination with amikacin antibiotics. Methods. The antibacterial activity of TH-NPs was evaluated using the broth microdilution method. Biofilm formation and antibiofilm assays were performed by the miniaturized microtiter plate method. Interaction studies between TH-NPs and amikacin against biofilm were determined using the checkerboard method. Results. TH-NPs exhibited antibacterial activity against planktonic cells of S. enterica serovars that were more efficient (8 to 32 times) than free thymol alone. S. Typhimurium and S. Choleraesuis isolates were considered strong biofilm producers. The combination of TH-NPs with amikacin showed synergistic activity in the inhibition and eradication of S. enterica serovar biofilm. The minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC) of amikacin were reduced by 32 to 128-fold when used in combination with TH-NPs. Time-kill kinetic studies showed that the combination of TH-NPs with amikacin possesses bactericidal action. Conclusion. This study suggests that the combination of TH-NPs with amikacin can be an alternative to overcome biofilm-associatedSalmonella diseases and therefore should be further explored as a model to search for new antibiofilm drugs.

Susceptibility Patterns in Staphylococcus and Klebsiella Causing Nosocomial Infections upon Treatment with E-Anethole-Rich Essential Oil from Clausena anisata

“…A similar trend was reported by several authors [49,50] after the determination of MIC and MBC correlations following the incubation of selected bacteria with extracts and/or essential oil from plants. Other authors reached similar conclusions while working on the influence of natural and synthetic compounds vis-à-vis the kinetics of bacterial mortality as a function of time (time-kill kinetics) [51][52][53][54][55]. The observed antibacterial activity might be attributed to the presence of a number of monoterpenes (E-anethole, methyl isoeugenol, myrcene sabinene and γ-terpinene) in the plant, which were mainly dominated by E-anethole (70.77%).…”

Poly-Gamma-Glutamic Acid Nanopolymer Effect against Bacterial Biofilms: In Vitro and In Vivo Study

“…Antibiotic-loaded polymer nanoparticles have been detected for their high physical characteristics and antibiofilm efficacy, so they could be used as drug delivery vehicles in the treatment of bacterial biofilm with low doses. Tokam et al ( 2023) found that thymol-loaded PLGA nanoparticles showed that MBEC and MBIC of Salmonella typhi, S. typhimurium, and S. choleraesuis were reduced by 32 to 128-fold [57], which was more effective than (8 to 32 times) free thymol. This is because of the high interaction between them and biofilms.…”

Essential-Oils-Loaded Biopolymeric Nanoparticles as Strategies for Microbial and Biofilm Control: A Current Status

“…The synergy of EOs and different antibiotics/drugs in nanoformulations has also been evaluated in different biofilms. In this context, the combination of thymol-loaded NPs and amikacin antibiotics was evaluated in Salmonella enterica serovars , which causes typhoidal and nontyphoidal salmonellosis [ 148 ]. The authors reported that the minimum biofilm inhibitory concentration was reduced four to eight times with the synergistic mechanism compared with the inhibition of amikacin alone.…”