Inhibition of Acinetobacter baumannii Biofilm Formation by Terpenes from Oregano (Lippia graveolens) Essential Oil

Abstract

Acinetobacter baumannii is a nosocomial pathogen known for its ability to form biofilms, leading to persistent infections and antibiotic resistance. The limited effective antibiotics have encouraged the development of innovative strategies such as using essential oils and their constituents. This study evaluated the efficacy of oregano (Lippia graveolens) essential oil (OEO) and its terpene compounds, carvacrol and thymol, in inhibiting A. baumannii biofilms. These treatments showed a minimum inhibitory concentration of 0.6, 0.3, and 2.5 mg/mL and a minimum bactericidal concentration of 1.2, 0.6, and 5 mg/mL, respectively. Sub-inhibitory doses of each treatment and the OEO significantly reduced biofilm biomass and the covered area of A. baumannii biofilms as measured by fluorescence microscopy. Carvacrol at 0.15 mg/mL exhibited the most potent efficacy, achieving a remarkable 95% reduction. Sub-inhibitory concentrations of carvacrol significantly reduced the biofilm formation of A. baumannii in stainless steel surfaces by up to 1.15 log CFU/cm2 compared to untreated bacteria. The OEO and thymol exhibited reductions of 0.6 log CFU/cm2 and 0.4 log CFU/cm2, respectively, without affecting cell viability. Moreover, the terpenes inhibited twitching motility, a crucial step in biofilm establishment, with carvacrol exhibiting the highest inhibition, followed by OEO and thymol. The study provides valuable insights into the potential of terpenes as effective agents against A. baumannii biofilms, offering promising avenues for developing novel strategies to prevent persistent infections and overcome antibiotic resistance.

Lippia graveolens Essential Oil to Enhance the Effect of Imipenem against Axenic and Co-Cultures of Pseudomonas aeruginosa and Acinetobacter baumannii

“…Moreover, these plant compounds combined with imipenem not only inhibited biofilm formation but also reduced the effective doses of the antibacterials required, which is in line with the strategy to combat bacterial resistance by using natural compounds that can disrupt biofilm formation and quorum sensing mechanisms [39,52,[70][71][72]. The combination treatments have shown potential for inhibiting biofilms by acting on different target sites and stages of biofilm development [27,[73][74][75][76][77][78][79][80][81][82][83]. This multipronged approach, targeting both the bacterial cell wall and disrupting biofilm integrity, holds the potential for more effective treatment strategies, providing an innovative direction in the fight against resistant bacterial infections.…”

“…Biofilm formation in bacteria like P. aeruginosa and A. baumannii can significantly contribute to their resistance to antibiotics [27,39,64,65]. Recent research has highlighted the complexity of biofilm-associated antibiotic resistance.…”

“…In this regard, the use of plant compounds has proven to be a good option as they exhibit characteristics such as low toxicity, accessibility, extensive medicinal use, and above all, a high antibacterial capacity related to their phytochemical composition [21][22][23]. A plant with great antibacterial activity is oregano in its different species (Origanum vulgare and Lippia graveolens), which has proven to be effective against microorganisms such as Candida albicans, methicillin-resistant Staphylococcus aureus (MRSA), Salmonella enterica, P. aeruginosa and A. baumannii [24][25][26][27]. This effectiveness is attributed to its main terpene compounds, carvacrol and thymol.…”

Stability study in selected conditions and biofilm-reducing activity of phages active against drug-resistant Acinetobacter baumannii

“…Interestingly Tapia-Rodriguez et al . observed that oregano essential oils as well as terpene compounds carvacrol and thymol showed an ability to inhibit A. baumannii biofilm development and indicated that carvacrol reduced the structure even in 95% at concentration 0.15 mg/mL 74 . The abovementioned studies indicate that there is a possibility to also use essential oils in combating biofilm produced by A. baumannii strains.…”

Biological activities of essential oils: A mini-review

“…It is noteworthy that some essential oils may also exhibit mutagenic activity. The essential oil of Lippia graveolens has been demonstrated to exert an inhibitory effect on the formation of Acinetobacter Baumanni formation, affecting twitwching motility [17].…”