Effects of Melaleuca alternifolia Chell (Tea Tree) and Eucalyptus globulus Labill. Essential Oils on Antibiotic-Resistant Bacterial Biofilms

Leptospira biofilms: implications for survival, transmission, and disease management

Leptospirosis is a zoonotic disease caused by Leptospira bacteria, affecting humans and a broad range of wild and domestic animals in diverse epidemiological settings (rural, urban, and wild). The disease's pathogenesis and epidemiology are complex networks not fully elucidated. Epidemiology reflects the One Health integrated approach of environment-animal-human interaction, causing severe illness in humans and animals, with consequent public health burdens. Saprophytic and pathogenic leptospires have been shown to form biofilms in vivo, in vitro, and in environmental samples. Biofilms are characterized by a polymeric matrix that confers protection against hostile environments (both inside and outside of the host), favoring bacterial survival and dissemination. Despite its significance, the role of this bacterial growth mode in leptospiral survival, transmission, and decreased antibiotic susceptibility remains poorly understood and underexplored. Even so, the literature indicates that biofilms might be correlated with lower antimicrobial susceptibility and chronicity in leptospirosis. In this minireview, we discuss the aspects of biofilm formation by Leptospira and their significance for epidemiology and therapeutic management. Understanding the current scenario provides insight into the future prospects for biofilm diagnosis, prevention, and treatment of leptospirosis.

Antibiofilm Effects of Novel Compounds in Otitis Media Treatment: Systematic Review

Otitis media (OM) is a frequent disease with incidence rate of 5300 cases per 100,000 people. Recent studies showed that polymicrobial biofilm formation represents a significant pathogenic mechanism in recurrent and chronic forms of OM. Biofilm enables bacteria to resist antibiotics that would typically be recommended in guidelines, contributing to the ineffectiveness of current antimicrobial strategies. Given the challenges of successfully treating bacterial biofilms, there is an growing interest in identifying novel and effective compounds to overcome antibacterial resistance. The objective of this review was to provide an overview of the novel compounds with antibiofilm effects on bacterial biofilm formed by clinical isolates of OM. The systematic review included studies that evaluated antibiofilm effect of novel natural or synthetic compounds on bacterial biofilm formed from clinical isolates obtained from patients with OM. The eligibility criteria were defined using the PICOS system: (P) Population: all human patients with bacterial OM; (I) Intervention: novel natural or synthetic compound with biofilm effect; (C) Control standard therapeutic antimicrobial agents or untreated biofilms, (O) Outcome: antibiofilm effect (biofilm inhibition, biofilm eradication), (S) Study design. The PRISMA protocol for systematic reviews and meta-analysis was followed. From 3564 potentially eligible studies, 1817 duplicates were removed, and 1705 were excluded according to defined exclusion criteria. A total of 41 studies with available full texts were retrieved by two independent authors. Fifteen articles were selected for inclusion in the systematic review which included 125 patients with OM. A total of 17 different novel compounds were examined, including N-acetyl-L-cysteine (NAC), tea tree oil, xylitol, eugenol, Aloe barbadensis, Zingiber officinale, Curcuma longa, Acacia arabica, antisense peptide nucleic acids, probiotics Streptococcus salivarius and Streptococcus oralis, Sodium 2-mercaptoethanesulfonate (MESNA), bioactive glass, green synthesized copper oxide nanoparticles, radish, silver nanoparticles and acetic acid. Staphylococcus aureus was the most commonly studied pathogen, followed by Pseudomonas aeruginosa and Haemophilus influenzae. Biofilm inhibition only by an examined compound was assessed in six studies; biofilm eradication in four studies, and both biofilm inhibition and biofilm eradication were examined in five studies. This systematic review indicates that some compounds like NAC, prebiotics, nanoparticles and MESNA that have significant effects on biofilm are safe and could be researched more extensively for further clinical use. However, a lack of data about reliable and efficient compounds used in therapy of different types of otitis media still remains in the literature.

The potency of Cupressus sempervirens and Eucalyptus globulus Essential Oils Against Antibiotic-Resistant Escherichia coli and Mammaliicoccus sciuri from Diseased Animals in Tunisia

This study aimed to investigate the antibacterial activity of essential oils from Cupressus sempervirens (CSEO) and Eucalyptus globulus (EGEO) against clinical isolates of colistin-resistant E. coli and methicillin-resistant M. sciuri recovered from diseased food-producing animals in Tunisia. The chemical compositions of both essential oils were analyzed using Gas chromatography-mass spectrometry (GC-MS). Antibacterial activity was determined through disk diffusion and microdilution assays, while the fractional inhibitory concentration index (FICI) was used to measure the synergistic effect of CSEO and colistin. The major constituents of CSEO were α-pinene (59.03%), δ-3 Carene (21.48%), D-limonene (5.62%) and α-thujene (3.08%), while EGEO contained eucalyptol (52.1%), α-pinene (26.51%), γ-terpinene (4.81%) and D-limonene (3.54%). The inhibition zone diameters (IZDs) against E. coli and M. sciuri ranged from 6 to 29 mm for CSEO and 9.3 to 28.6 mm for EGEO. Minimum inhibitory concentrations (MICs) showed a range of 4 to 512 µg/mL for CSEO against M. sciuri and 2 to 426.66 µg/mL for EGEO. For E. coli, MICs ranged from 170.66 to 512 µg/mL for CSEO and 53.33 to 512 µg/mL for EGEO. The checkerboard test demonstrated a synergistic effect between CSEO and colistin against two colistin-resistant E. coli isolates, with FICI 3- to 32-fold lower than the MICs of the individual compounds. This study highlights the potency of essential oils from CSEO and EGEO against antibiotic-resistant M. sciuri and E. coli strains from animals in Tunisia and provides evidence of the synergistic effect between CSEO and colistin against clinically relevant colistin-resistant E. coli isolates.

Enhancing Antibiotic Efficacy and Combating Biofilm Formation: Evaluating the Synergistic Potential of Origanum vulgare Essential Oil against Multidrug-Resistant Gram-Negative Bacteria

Multidrug-resistant (MDR) Gram-negative bacteria remain a global public health issue due to the barrier imposed by their outer membrane and their propensity to form biofilms. It is becoming imperative to develop new antibacterial strategies. In this context, this study aims to evaluate the antibacterial efficacy of Origanum vulgare essential oil (OEO), alone and in combination with antibiotics, as well as its antibiofilm action against multidrug-resistant Gram-negative strains. OEO components were identified by gas chromatography-mass spectrometry (GC-MS), and antibacterial activity was assessed using the agar diffusion test and the microdilution method. Interactions between OEO and antibiotics were examined using the checkerboard method, while antibiofilm activity was analyzed using the crystal violet assay. Chemical analysis revealed that carvacrol was the major compound in OEO (61.51%). This essential oil demonstrated activity against all the tested strains, with inhibition zone diameters (IZDs) reaching 32.3 ± 1.5 mm. The combination of OEO with different antibiotics produced synergistic and additive effects, leading to a reduction of up to 98.44% in minimum inhibitory concentrations (MICs). In addition, this essential oil demonstrated an ability to inhibit and even eradicate biofilm formation. These results suggest that OEO could be exploited in the development of new molecules, combining its metabolites with antibiotics.

Candida krusei M4CK Produces a Bioemulsifier That Acts on Melaleuca Essential Oil and Aids in Its Antibacterial and Antibiofilm Activity

Surface-active compounds (SACs) of microbial origin are an active group of biomolecules with potential use in the formulation of emulsions. In this sense, the present study aimed to isolate and select yeasts from fruits that could produce SACs for essential oil emulsions. The Candida krusei M4CK was isolated from the Byrsonima crassifolia fruit to make SACs. This emulsification activity (E24) was equal to or greater 50% in all carbon sources, such as olive oil, sunflower oil, kerosene, hexane, and hexadecane. E24 followed exponential growth according to the growth phase. The stability of emulsions was maintained over a wide range of temperatures, pH, and salinity. The OMBE4CK (melaleuca essential oil emulsion) had better and more significant inhibitory potential for biofilm reduction formation. In addition, bioemulsifier BE4CK alone on Escherichia coli and Pseudomonas aeruginosa biofilm showed few effective results, while there was a significant eradication for Staphylococcus aureus biofilms. The biofilms formed by S. aureus were eradicated in all concentrations of OMBE4CK. At the same time, the preformed biofilm by E. coli and P. aeruginosa were removed entirely at concentrations of 25 mg/mL, 12.5 mg/mL, and 6.25 mg/mL. The results show that the bioemulsifier BE4CK may represent a new potential for antibiofilm application.

Tea Tree Oil: Properties and the Therapeutic Approach to Acne-A Review

Acne vulgaris is an inflammatory dermatological pathology that affects mostly young people. However, it can also appear in adulthood, mainly in women. It has a high psychosocial impact, not only at the time of active lesions but also due to the consequences of lesions such as scarring and hyperpigmentation. Several factors are involved in the physiopathology of acne and the constant search for active ingredients is a reality, namely phytotherapeutic ingredients. Tea tree oil is an essential oil extracted from Melaleuca alternifolia (Maiden & Betch) Cheel with known antibacterial, anti-inflammatory, and antioxidant properties, making it a candidate for the treatment of acne. This review aims to describe the various properties of tea tree oil that make it a possible ingredient to use in the treatment of acne and to present several human studies that have evaluated the efficacy and safety of using tea tree oil in the treatment of acne. It can be concluded that tea tree oil has good antibacterial, anti-inflammatory, and antioxidant properties that result in a decrease in the number of inflammatory lesions, mainly papules, and pustules. However, given the diversity of study designs, it is not possible to draw concrete conclusions on the efficacy and safety of this oil in the treatment of acne.

Synergistic Inhibition of Methicillin-Resistant Staphylococcus aureus (MRSA) by Melaleuca alternifolia Chell (Tea Tree) and Eucalyptus globulus Labill. Essential Oils in Association with Oxacillin

The presence of antibiotic-resistant bacteria has become a major therapeutic priority. This trend indicates the need for alternative agents to antibiotics, such as natural compounds of plant origin. By assessing membrane permeability, we investigated the antimicrobial activity of Melaleuca alternifolia and Eucalyptus globulus essential oils (EOs) against three strains of methicillin-resistant Staphylococcus aureus (MRSA). Using the checkerboard method, the efficacy of single EOs, in association with each other or in combination with oxacillin, was quantified by calculating the fractional inhibitory concentrations (FIC Index). All EOs showed a reduction in bacterial load, an alteration of membrane permeability which leads to an increase in its function, resulting in the release of nucleic acids and proteins. The treatment with EO-oxacillin combinations and associated EO-EO resulted in a synergistic effect in most of the tests performed. EO-EO association showed a high activity in the alteration of the membrane, increasing the permeability to about 80% in all the MRSA strains treated. In conclusion, the combination of EOs and antibiotics represents a valid therapeutic support against MRSA bacteria, allowing for a decrease in the antibiotic concentration needed for therapeutic use.