Synergistic effect of Myrtus communis L. essential oils and conventional antibiotics against multi-drug resistant Acinetobacter baumannii wound isolates

The Combinatory Effects of Essential Oil from Lippia macrophylla on Multidrug Resistant Acinetobacter baumannii Clinical Isolates

To assess the antibacterial effectiveness of Lippia macrophylla essential oil (LMEO) against multidrug-resistant Acinetobacter baumannii isolates, both as a standalone treatment and in combination with conventional antibiotics. LMEO demonstrated a significant inhibitory effect on the growth of A. baumannii, with a minimum inhibitory concentration (MIC) below 500 μg/mL. Notably, LMEO was capable of reversing the antibiotic resistance of clinical isolates or reducing their MIC values when used in combination with antibiotics, showing synergistic (FICI≤0.5) or additive effects. The combination of LMEO and imipenem was particularly effective, displaying synergistic interactions for most isolates. Ultrastructural analyses supported these findings, revealing that the combination of LMEO+ceftazidime compromised the membrane integrity of the Acb35 isolate, leading to cytoplasmic leakage and increased formation of Outer Membrane Vesicles (OMVs). Taken together our results point for the use of LMEO alone or in combination as an antibacterial agent against A. baumannii. These findings offer promising avenues for utilizing LMEO as a novel antibacterial strategy against drug-resistant infections in healthcare settings, underscoring the potential of essential oils in enhancing antibiotic efficacy.

Exploring Biofilm-Related Traits and Bile Salt Efficacy as Anti-Biofilm Agents in MDR Acinetobacter baumannii

Acinetobacter baumannii has been designated as a critical priority pathogen by the World Health Organization for the development of novel antimicrobial agents. This study aimed to investigate both the phenotypic and genotypic traits of multidrug-resistant (MDR) A. baumannii strains, along with the effects of natural bile salts on biofilm formation. The research analyzed phenotypic traits, including autoaggregation, hydrophobicity, twitching motility, lectin production, and biofilm formation, as well as genotypic traits such as the presence of bap and blaPER-1 genes in twenty wound and eight environmental MDR A. baumannii isolates. While all strains were identified as good biofilm producers, no statistically significant correlation was detected between the examined traits and biofilm formation. However, differences in biofilm production were observed between environmental and wound isolates. The natural bile salts Na-cholate, Na-deoxycholate, and Na-chenodeoxycholate demonstrated effective anti-A. baumannii activity (MIC = 0.25-10 mg mL-1), with significant anti-biofilm effects. Na-deoxycholate and Na-chenodeoxycholate inhibited 94-100% of biofilm formation at super-MIC concentrations (8-32 mg mL-1). This study underscores the urgent need for innovative strategies to combat antibiotic resistance and biofilm formation in A. baumannii, highlighting the potential of natural bile salts as promising biofilm inhibitors and encouraging further research into their modification and combination with other antimicrobials.

The therapeutic value of Myrtus communis L.: an updated review

Myrtus communis L. (Family: Myrtaceae) is naturally found in the western part of Asia, Southern Europe, and North Africa. It has been reportedly applied in pharmaceutical industry, traditional medicine, cosmetics, spices, and food. Pubmed, Google scholar, Web of Science, and Scopus were utilized to seek out relevant content concerning the therapeutic potential of M. communis. Subsequently, we conducted a review to identity noteworthy updates pertaining to M. communis. Myrtle berries, leaves, seeds, and essential oils are natural sources of several nutrients and bioactive compounds with marked health effects. The chemical analysis showed that M. communis contained oils, alkaloids, flavonoids, phenolics, coumarins, saponosides, tannins, quinines, and anthraquinones. A pharmacological investigation revealed that M. communis possessed anti-inflammatory, analgesic, antimicrobial, antiparasitic, antioxidant, antidiabetic, anticancer, antimutagenic, immunomodulatory, dermatological, cardiovascular, central nervous system, and gastrointestinal protective effects, among numerous other biological effects. This current review focused on the biochemical, pharmacological, therapeutic effects, and various biological activities of different parts of M. communis. It signifies that M. communis is a therapeutic plant with numerous applications in medicine and could be used as a drug isolate based on its safety and effectiveness.

First Characterization of Acinetobacter baumannii-Specific Filamentous Phages

Filamentous bacteriophages belonging to the order Tubulavirales, family Inoviridae, significantly affect the properties of Gram-negative bacteria, but filamentous phages of many important pathogens have not been described so far. The aim of this study was to examine A. baumannii filamentous phages for the first time and to determine their effect on bacterial virulence. The filamentous phages were detected in 15.3% of A. baumannii strains as individual prophages in the genome or as tandem repeats, and a slightly higher percentage was detected in the culture collection (23.8%). The phylogenetic analyses revealed 12 new genera within the Inoviridae family. Bacteriophages that were selected and isolated showed structural and genomic characteristics of the family and were unable to form plaques. Upon host infection, these phages did not significantly affect bacterial twitching motility and capsule production but significantly affected growth kinetics, reduced biofilm formation, and increased antibiotic sensitivity. One of the possible mechanisms of reduced resistance to antibiotics is the observed decreased expression of efflux pumps after infection with filamentous phages.

Synergistic interaction of polymyxin B with carvacrol: antimicrobial strategy against polymyxin-resistant Klebsiella pneumoniae

Objective: The antimicrobial activities of the synergistic combination of carvacrol and polymyxin B against polymyxin-resistant Klebsiella pneumoniae were evaluated. Methods: The methods employed checkerboard assays to investigate synergism, biofilm inhibition assessment and membrane integrity assay. In addition, the study included in vivo evaluation using a mouse infection model. Results: The checkerboard method evaluated 48 combinations, with 23 indicating synergistic action. Among these, carvacrol 10 mg/kg plus polymyxin B 2 mg/kg exhibited in vivo antimicrobial activity in a mouse model of infection, resulting in increased survival and a significant decrease in bacterial load in the blood. Conclusion: Polymyxin in synergy with carvacrol represents a promising alternative to be explored in the development of new antimicrobials.

Effects of Chloride and Sulfate Salts on Seed Germination and Seedling Growth of Ballota hirsuta Benth. and Myrtus communis L

Soil salinity is a well-known abiotic factor affecting the germination and seedling growth of various plant species. Therefore, we evaluated the effects of different chloride salts (NaCl, KCl and MgCl2) and sulfate salts (Na2SO4, K2SO4 and MgSO4) on the seed germination and early seedling growth of two important ethnomedicinal shrubs of North Africa and the Mediterranean basin (Ballota hirsuta and Myrtus communis). Seeds of these species were subjected to five salinity levels (0-100 mM) and incubated at 20 °C under a light regime (12 h photoperiod). Both species demonstrated their highest germination percentage under control conditions (i.e., without salinity). However, as salinity levels increased, the germination percentages for both species decreased, regardless of the type of salt used. Cations appeared to be more determinative than the anions in regulating the seed germination of both species. M. communis seeds displayed greater sensitivity to sodium (Na+) salts, especially when accompanied with chloride (Cl-) anions. At the higher salt concentrations (75 and 100 mM), Na+ salts had a more pronounced inhibitory effect on M. communis seedling growth compared to potassium (K+) and magnesium (Mg2+) salts. Conversely, Mg2+ salts were more detrimental to seedling growth in B. hirsuta. Based on our results, it can be concluded that both of these species are able to tolerate a moderate level of salinity. Overall, B. hirsuta may be a promising choice for rehabilitating the soils dominated by chloride salts, while M. communis could be utilized for restoring sulfate-dominated soils.

Partnering essential oils with antibiotics: proven therapies against bovine Staphylococcus aureus mastitis

Introduction

There is an urgent need to develop therapeutic options for biofilm-producing Staphylococcus aureus (S. aureus). Therefore, the renewed interest in essential oils (EOs), especially carvacrol, linalool and eugenol, has attracted the attention of our research group.

Methods

Multidrug resistance and multivirulence profiles in addition to biofilm production of S. aureus strains isolated from cows with mastitis were evaluated using both phenotypic and genotypic methods. The antimicrobial and antibiofilm activities of EOs were tested using both in vitro and molecular docking studies. Moreover, the interactions between commonly used antibiotics and the tested EOs were detected using the checkerboard method.

Results

We found that all our isolates (n= 37) were biofilm methicillin resistant S. aureus (MRSA) producers and 40.5% were vancomycin resistant S. aureus (VRSA). Unfortunately, 73 and 43.2% of the recovered MRSA isolates showed multidrug resistant (MDR) and multivirulence patterns, respectively. The antimicrobial activities of the tested EOs matched with the phenotypic evaluation of the antibiofilm activities and molecular docking studies. Linalool showed the highest antimicrobial and antibiofilm activities, followed by carvacrol and eugenol EOs. Fortunately, synergistic interactions between the investigated EOs and methicillin or vancomycin were detected with fractional inhibitory concentration index (FICI) values ≤ 0.5. Moreover, the antimicrobial resistance patterns of 13 isolates changed to sensitive phenotypes after treatment with any of the investigated EOs. Treatment failure of bovine mastitis with resistant S. aureus can be avoided by combining the investigated EOs with available antimicrobial drugs.

Conclusion

We hope that our findings can be translated into a formulation of new pharmaceutical dosage forms against biofilm-producing S. aureus pathogens.

Essential oils and their active components applied as: free, encapsulated and in hurdle technology to fight microbial contaminations. A review

Microbial contaminations are responsible for many chronic, healthcare, persistent microbial infections and illnesses in the food sector, therefore their control is an important public health challenge. Over the past few years, essential oils (EOs) have emerged as interesting alternatives to synthetic antimicrobials as they are biodegradable, extracted from natural sources and potent antimicrobials. Through their multiple mechanisms of actions and target sites, no microbial resistance has been developed against them till present. Although extensive documentation has been reported on the antimicrobial activity of EOs, comparisons between the use of whole EOs or their active components alone for an antimicrobial treatment are less abundant. It is also essential to have a good knowledge about EOs to be used as alternatives to the conventional antimicrobial products such as chemical disinfectants. Moreover, it is important to focus not only on planktonic vegetative microorganisms, but to study also the effect on more resistant forms like spores and biofilms. The present article reviews the current knowledge on the mechanisms of antimicrobial activities of EOs and their active components on microorganisms in different forms. Additionally, in this review, the ultimate advantages of encapsulating EOs or combining them with other hurdles for enhanced antimicrobial treatments are discussed.

Recent advances to combat ESKAPE pathogens with special reference to essential oils

Biofilm-associated bacteria, especially ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.), are a serious challenge worldwide. Due to the lack of discovery of novel antibiotics, in the past two decades, it has become necessary to search for new antibiotics or to study synergy with the existing antibiotics so as to counter life-threatening infections. Nature-derived compounds/based products are more efficient than the chemically synthesized ones with less resistance and lower side effects. In this descriptive review, we discuss the most promising therapeutics for the treatment of ESKAPE-related biofilms. The first aspect includes different types of natural agents [botanical drugs, essential oils (EOs), antimicrobial peptides, bacteriophages, and endolysins] effective against ESKAPE pathogens. The second part of the review deals with special references to EOs/essential oil components (EOCs) (with some exclusive examples), mode of action (via interfering in the quorum-sensing pathways, disruption of biofilm and their inhibitory concentrations, expression of genes that are involved, other virulence factors), existing in literature so far. Moreover, different essential oils and their major constituents were critically discussed using in vivo models to target ESKAPE pathogens along with the studies involving existing antibiotics.

Nanoemulsion as an Effective Inhibitor of Biofilm-forming Bacterial Associated Drug Resistance: An Insight into COVID Based Nosocomial Infections

Antibiotic overuse has resulted in the microevolution of drug-tolerant bacteria. Understandably it has become one of the most significant obstacles of the current century for scientists and researchers to overcome. Bacteria have a tendency to form biofilm as a survival mechanism. Biofilm producing microorganism become far more resistant to antimicrobial agents and their tolerance to drugs also increases. Prevention of biofilm development and curbing the virulency factors of these multi drug resistant or tolerant bacterial pathogens is a newly recognised tactic for overcoming the challenges associated with such bacterial infections and has become a niche to be addressed. In order to inhibit virulence and biofilm from planktonic bacteria such as, Pseudomonas aeruginosa, Acinetobacter baumannii, and others, stable nanoemulsions (NEs) of essential oils (EOs) and their bioactive compounds prove to be an interesting solution. These NEs demonstrated significantly greater anti-biofilm and anti-virulence activity than commercial antibiotics. The EO reduces disease-causing gene expression, which is required for pathogenicity, biofilm formation and attachment to the surfaces. Essential NE and NE-loaded hydrogel surface coatings demonstrates superior antibiofilm activity which can be employed in healthcare-related equipments like glass, plastic, and metal chairs, hospital beds, ventilators, catheters, and tools used in intensive care units. Thus, anti-virulence and anti-biofilm forming strategies based on NEs-loaded hydrogel may be used as coatings to combat biofilm-mediated infection on solid surfaces.

Combination Strategies of Different Antimicrobials: An Efficient and Alternative Tool for Pathogen Inactivation

Despite the discovery and development of an array of antimicrobial agents, multidrug resistance poses a major threat to public health and progressively increases mortality. Recently, several studies have focused on developing promising solutions to overcome these problems. This has led to the development of effective alternative methods of controlling antibiotic-resistant pathogens. The use of antimicrobial agents in combination can produce synergistic effects if each drug invades a different target or signaling pathway with a different mechanism of action. Therefore, drug combinations can achieve a higher probability and selectivity of therapeutic responses than single drugs. In this systematic review, we discuss the combined effects of different antimicrobial agents, such as plant extracts, essential oils, and nanomaterials. Furthermore, we review their synergistic interactions and antimicrobial activities with the mechanism of action, toxicity, and future directions of different antimicrobial agents in combination. Upon combination at an optimum synergistic ratio, two or more drugs can have a significantly enhanced therapeutic effect at lower concentrations. Hence, using drug combinations could be a new, simple, and effective alternative to solve the problem of antibiotic resistance and reduce susceptibility.

Adjuvant antimicrobial activity and resensitization efficacy of geraniol in combination with antibiotics on Acinetobacter baumannii clinical isolates

Adjuvant use of geraniol, a plant essential oil component, is known to increase the efficacy of antibiotics by acting as a potent inhibitor of efflux mechanisms. In this study, we assessed the effect of a geraniol–antibiotic combination in 21 Acinetobacter baumannii clinical isolates consisting of high efflux (HE) and low efflux (LE) activity groups. We determined the MIC for geraniol and the four antibiotics and evaluated the adjuvant antimicrobial activity and resensitization efficacy of adjuvant geraniol. Geraniol–antibiotic combinations significantly reduced the MIC of all four antibiotics (P < 0.0001), and the fold change in MIC decreased by 4 to >256-fold for tigecycline, >16 to >4,096-fold for ceftazidime, 1 to >4,096-fold for cefepime, and >2 to >4096-fold for ciprofloxacin. Importantly, geraniol showed adjuvant antimicrobial activity and resensitization efficacy when used in combination with antibiotics in 21 A. baumannii clinical isolates. However, there was no statistically significant difference between the HE and LE groups. Low concentrations (0.125% and 0.0625%) of geraniol showed no cytotoxic or hemolytic activity. Our study shows that geraniol, acting as an antibiotic adjuvant, is a good candidate for in vivo studies of combination therapy for the treatment of MDR/XDR A. baumannii infections.

An Optimized Checkerboard Method for Phage-Antibiotic Synergy Detection

Phage-antibiotic synergy is a promising therapeutic strategy, but there is no reliable method for synergism estimation. Although the time-kill curve assay is a gold standard, the method is not appropriate for fast and extensive screening of the synergy. The aim is to optimize the checkerboard method to determine phage-chemical agent interactions, to check its applicability by the time-kill curve method, and to examine whether the synergy can be obtained with both simultaneous and successive applications of these agents. In addition, the aim is to determine interactions of the Pseudomonas phage JG024 with ciprofloxacin, gentamicin, or ceftriaxone, as well as the Staphylococcus phage MSA6 and SES43300 with ciprofloxacin, gentamicin, and oxacillin. The results show that the optimized checkerboard method is reliable and that results correspond to those obtained by the time-kill curve. The synergy is detected with the phage JG024 and ciprofloxacin or ceftriaxone against Pseudomonas aeruginosa, and the phage SES43300 with ciprofloxacin against MRSA. The synergy was obtained after simultaneous applications, and in the case of P. aeruginosa, after application of the second agent with delay of one hour, indicating that simultaneous application is the best mode of synergy exploitation for therapy. The checkerboard method can be used for thorough clinical studies on synergy and in the future for personalized therapy when infections are caused by multiple resistant bacteria.

Evaluation of sulbactam and colistin/sulbactam efficacy against multiple resistant Acinetobacter baumannii blood isolates

PURPOSE

We aimed to compare the results of the BD Phoenix (TM) M50 ID/AST system and the gold standard broth microdilution method. We also evaluated the potential of a new therapeutic combination (colistin/sulbactam) for colistin resistance among Acinetobacter baumanni strains.

METHODS

Growth in blood samples was detected with the BACTEC (BD Becton Dickinson, ABD) continuous monitoring blood culture system. Strains were identified by Phoenix (BD Phoenix™ M50, ABD) automated bacterial identification system and antimicrobial susceptibility results were obtained. A total of 92 A. baumannii complex isolates showing resistance to at least three antibiotic classes were included in the study. Colistin susceptibility results (both susceptible and resistant strains) detected by the Phoenix device were confirmed by the reference method, the liquid microdilution method. The concentration index (FIC) was used to determine the efficacy of fractional inhibitor drug combinations, the efficacy of colistin/sulbactam combination against 50 multiresistant A. baumannii complex strains was investigated using the checkerboard method.

RESULTS

10 (10.9%) of 92 isolates were resistant to colistin and 80 (86.9%) to sulbactam. With the automation system, only 2 of 10 isolates were found resistant to colistin, while 8 isolates were susceptible. For this reason, the very major error rate of the Phoenix M50 automatic system among resistant isolates was determined as 8/10. It was determined that 6 (12%) of the colistin/sulbactam combination had a synergistic effect and 44 (88%) had an additive interaction. No antagonistic interaction was detected with the colistin-sulbactam combination in this study.

CONCLUSION

A. baumannii strains should be confirmed by the broth microdilution method, which is the reference method, against the MIC results detected by automated systems. It was concluded that the use of colistin alone should be avoided in the treatment of A. baumannii infections.

Materials for restoring lost Activity: Old drugs for new bugs

The escalation of bacterial resistance to conventional medical antibiotics is a serious concern worldwide. Improvements to current therapies are urgently needed to address this problem. The synergistic combination of antibiotics with other agents is a strategic solution to combat multi-drug-resistant bacteria. Although these combinations decrease the required high dosages and therefore, reduce the toxicity of both agents without compromising the bactericidal effect, they cannot stop the development of further resistance. Recent studies have shown certain elements restore the ability of antibiotics to destroy bacteria that have acquired resistance to them. Due to these synergistic activities, organic and inorganic molecules have been investigated with the goal of restoring antibiotics in new approaches that mitigate the risk of expanding resistance. Herein, we summarize recent studies that restore antibiotics once thought to be ineffective, but have returned to our armamentarium through innovative, combinatorial efforts. A special focus is placed on the mechanisms that allow the synergistic combinations to combat bacteria. The promising data that demonstrated restoration of antimicrobials, supports the notion to find more combinations that can combat antibiotic-resistant bacteria.

Biological control of Citrus brown spot pathogen, "Alternaria alternata" by different essential oils

The antifungal effects of laurel, myrtle and peppermint essential oils and their combinations were investigated in vitro on two strains of Alternaria alternata mycelial growth and in vivo on detached Citrus leaf disease incidence. Myrtle essential oil was rich in α-pinene and 1,8-cineole while peppermint essential oil in menthol and menthone. 1,8-Cineole was the main component of the essential oils from laurel, laurel + myrtle and peppermint + laurel. The combined peppermint and myrtle essential oil was characterized by the predominance of menthol and 1,8-cineole. All tested essential oils, incorporated in potato-dextrose agar, inhibited A. alternata mycelial growth and had a fungistatic effect at concentration 3 mg/mL of medium. A great synergism was detected between peppermint and laurel essential oils against the two strains of A. alternata. The combined laurel and peppermint essential oil reduced mycelial growth rates of inoculated detached leaves at concentration above 1.5 mg/mL.

Botanic Garden as a Factory of Molecules: Myrtus communis L. subsp. communis as a Case Study

A novel perception of botanic gardens as complex “factories of molecules” (Lombardy Region Project–Lr. 25/2016, year 2021), that mediate plant–environment interactions, and are the basis of their utility for humans, is presented. The core-topic is the medicinal plant heritage of the Ghirardi Botanic Garden (Toscolano Maderno, Brescia, Italy) of the University of Milan. In this work, we studied Myrtus communis L. subsp. communis (Myrtaceae) at multiple scale levels: macro- and micromorphological, with special emphasis on the secretory structures responsible for the production of secondary metabolites; phytochemical, with the analysis of the essential oil (EO) composition from leaves (fresh, dried, stored at −20 °C and at −80 °C) and fruits over two consecutive years (2018 and 2019); bio-ecological, with a focus, based on literature data, on the ecology and biological activity of the main EO components. The occurrence of secretory cavities producing terpenes, along with flavonoids, was proven. A high level of chemical variability across the obtained EO profiles emerged, especially that concerning quantitative data. However, regardless of the different conservation procedures, the examined plant part, or the phenological stage, we detected the presence of three ubiquitous compounds: α-pinene, 1,8-cineole, and linalool. The overall results will serve to enrich the Ghirardi Botanic Garden with novel labeling showing accurate and updated scientific information in an Open science perspective.

Comparative evaluation of anti-inflammatory activity between n-butanol fraction, leaf and stem methanolic extract obtained from Olaxpsittacorum

ETHNOPHARMACOLOGICAL RELEVANCE

Olax psittacorum (Lam.) Vahl. traditionally used by the tribal communities of 'INDIA' to heal conditions such as pain, psoriasis, mouthulcer, anemia, constipation as well as diabetes followed by scientific evidences like antipyretic, anti-inflammatory, antimicrobial, anti-viral, and anti-cancer property too.

AIM OF THE EXPERIMENT

Solvent fractionation process by using chloroform, distilled water and n-butanol has been developed to get the precipitate as a fraction (encrypted as FrAE-ISO) of leaf methanolic extract (LME) and established GC-MS and antiinflammatory evaluation. The aim was to enumerate the potency against inflammation of FrAE-ISO comparing with LME, SME (Stem methanolic extract) and Diclofenac. TLC of LME extract has been developed too for separation & evaluation of the compounds appeared as bands obtained by scraping process. The motive of the experiment was to acquire an isolate from LME that can able to show an emense anti-inflammatory action compared to LME and SME.

MATERIALS AND METHODS

Priliminary phytochemical screening upon LME, SME and FrAE-ISO preformed by the standard methods of literatures. Scrapped portions of developed TLC plate (G-254 graded silica) of LME (n-Hexane:Ethylacetate; 7.5:2.5) were introduced to GC-MS evaluation. FrAE-ISO has introduced at a minute quantity (5 and 10 mg/kg/bw) within Wister albino rats (per os) against inflammation (model: carrageenan-induced paw edema) to evaluate its potency as compared to LME (25 mg/kg/bw), SME (25 mg/kg/bw) and Diclofenac (100 mg/kg). GC-MS evaluation has been conducted in both FrAE-ISO and scrapped sections to evaluate the presence of compounds qualitatively.

RESULTS

LME and SME, qualitatively through different screening processes confirm the presence of glycosides, flavonoids, amino acids, tannins, and saponins respectively. According to the quantitative study of the extracts concerning total phenolic, flavonoid, tannin, and saponin content equivalent to gallic acid, quercetin, tannic acid, and diosgenin respectively have shown less amount of phenolic, flavonoid, and saponin content in SME (30.95, 205.33 and 30.82 mg/g extract respectively) as compared to LME (95.68, 713.33 and 66.41 mg/g extract respectively). Quantitative estimation has shown the presence of 825.27 mg of saponin equivalent to diosgenin per gram of FrAE-ISO. The GC-MS study has revealed that every section of the leaf extract has " Hexadecanoic acid, methyl ester " in common with other important compounds responsible for its potent contribution towards the anti-inflammatory property. The scrapped portions of the TLC plate having mixture of compounds but FrAE-ISO has shown a sharp peak in GC-MS (up to 34 min of run time) as well as few crystals like structures under the binocular microscope. Compact doses of FrAEISO (yield = 1.645%) i.e. 5 and 10 mg/kg body weight was able to compete with 100 mg/kg Diclofenac portraying 88%-95% inhibition respectively throughout all phases of inflammation with no-significant differences compared to standard evaluated by ANOVA (in SPSS).

CONCLUSION

Olax psittacorum (Lam.) Vahl. could be a good choice to explore its importance within the pharmacognostic field of drug development and might be a better source of herbal-derived lead compounds which can help to treat other various activities like ulcer healing or anti-anemic property etc.

Optimized Antibacterial Effects in a Designed Mixture of Essential Oils of Myrtus communis, Artemisia herba-alba and Thymus serpyllum for Wide Range of Applications

Nowadays, the combination of molecules influences their biological effects, and interesting outcomes can be obtained from different component interactions. Using a mixture design method, this research seeks to simulate the efficacy of essential oil combinations against various bacteria and forecast the ideal combination. The chemical compositions of Myrtus communis, Artemisia herba-alba and Thymus serpyllum essential oils were analyzed using CG/MS. Then, the combined antibacterial effects were evaluated by testing mixture design formulations using the microdilution bioassay. The main compounds detected for M. communis essential oil were myrtenyl acetate (33.67%), linalool (19.77%) and 1,8-cineole (10.65%). A. herba-alba had piperitone as a chemotype, representing 85%. By contrast, the T. serpyllum oil contained thymol (17.29%), γ-terpinene (18.31%) and p-cymene (36.15%). The antibacterial effect of the essential oils studied, and the optimum mixtures obtained were target strain-dependent. T. serpyllum alone ensured the optimal inhibition against S. aureus and E. coli, while a ternary mixture consisting of 17.1%, 39.6% and 43.1% of M. communis, A. herba-alba and T. serpyllum respectively, was associated with optimal inhibitory activity against B. subtilis. The outcome of this research supports the idea of the boosting effect of essential oil combinations toward better activities, giving better understanding of the usefulness of mixture designs for food, cosmetics, and pharmaceutical applications.

Synergistic activity of bile salts and their derivatives in combination with conventional antimicrobial agents against Acinetobacter baumannii

ETHNOPHARMACOLOGICAL RELEVANCE

Bile traditionally was used in wound healing, having erodent, antioxidant and antimicrobial potential. Acinetobacter baumannii is a frequent etiological agent of wound infections, exhibiting high level of resistance to conventional antibiotics.

AIM OF THE STUDY

To determine the effect of selected bile acid sodium salts and their 3-dehydro (i.e. 3-oxo) derivatives, as well as their combinations with commercial antibiotics against A. baumanniia, to confirm bile ethnopharmacological application in wound healing from aspect of microbiology.

MATERIALS AND METHODS

The sensitivity of reference and multidrug resistant (MDR) A. baumannii strains to bile salts, their derivatives and conventional antibiotics were examined by a microtiter plate method. The interaction of bile salts/derivatives and antibiotics was examined by a checkerboard method and time kill curve method. The interaction of bile salts with ciprofloxacin in terms of micelles formation was examined by DOSY NMR technique.

RESULTS

The bile salts sodium deoxycholate (Na-DCA) and sodium chenodeoxycholate (Na-CDCA), as well as their derivatives sodium 3-dehydro-deoxycholate (Na-3DH-DCA) and sodium 3-dehydro-chenodeoxycholate (Na-3DH-CDCA), potentiate antibiotic activity and resensitize A. baumannii. The bile salts and their derivatives enhance A. baumannii sensitivity to antibiotics, particularly those that should penetrate cell to exhibit activity. The sodium salts of bile acid derivatives, namely Na-3DH-DCA and Na-3DH-CDCA, showed synergy against both reference and MDR strain in combination with ciprofloxacin or gentamicin, while synergy with gentamicin was obtained in all combinations, regardless of bile salt type and bacterial strains. The synergy with Na-3DH-CDCA was further confirmed by the time-kill curve method, as bacterial number decreased after 12 h. NMR experiment revealed that this bile salt derivative and ciprofloxacin form co-aggregates when bile salts concentration was higher than critical micelle concentrations (CMC), which indicate the possibility that bile salts enhance ciprofloxacin cell penetration by membrane destabilization, contributing to the synergy.

CONCLUSION

The synergistic interactions between bile salts or derivatives with ciprofloxacin and particularly gentamicin represent a promising strategy for the treatment of A. baumannii wound infections.

Antimicrobial Mechanism and Identification of the Proteins Mediated by Extracts from Asphaltum punjabianum and Myrtus communis

Myrtus communis ("myrtle") and Asphaltum punjabianum ("shilajeet") are a medicinal plant and a long-term-humified dead plant material, respectively. We studied their antibacterial and anticandidal activities against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Candida albicans. The activities of the aqueous extracts of the studied materials were measured using agar-well diffusion methods. Furthermore, proteomic analysis of treated microbial cells was conducted to identify affected proteins. The results showed both antibacterial and anticandidal activities for the myrtle extract (ME), while the shilajeet extract (SE) showed antibacterial activity only. The highest antimicrobial activity was observed against E. coli among the microbes tested; therefore, it was taken as the model for the proteomic analysis to identify the antimicrobial mechanism of ME and SE using two-dimensional electrophoresis. Upregulation of expression of 42 proteins and downregulation of expression of 6 proteins were observed in E. coli treated with ME, whereas 12 upregulated and 104 downregulated proteins were detected in E. coli treated with SE, in comparison with the control. About 85% of identified expressed proteins were from the cytoplasm and 15% from microbial cell walls, indicating the penetration of extracts inside cells. A higher percentage of expressed proteins was recorded for enzymatic activity. Our findings suggest that the major targets of the antibacterial action were proteins involved in the outer membrane, oxidative stress, and metabolism. Our data might reveal new targets for antimicrobial agents.

Multidrug and Pan-Antibiotic Resistance—The Role of Antimicrobial and Synergistic Essential Oils: A Review

Bacterial resistance to antibiotics continues to be a grave threat to human health. Because antibiotics are no longer a lucrative market for pharmaceutical companies, the development of new antibiotics has slowed to a crawl. The World Health Organization reported that the 8 new bacterial agents approved since July 2017 had limited clinical benefits. While a cohort of biopharmaceutical companies recently announced plans to develop 2-4 new antibiotics by 2030, we needn’t wait a decade to find innovative antibiotic candidates. Essential oils (EOs) have long been known as antibacterial agents with wide-ranging arsenals. Many are able to penetrate the bacterial membrane and may also be effective against bacterial defenses such as biofilms, efflux pumps, and quorum sensing. EOs have been documented to fight drug-resistant bacteria alone and/or combined with antibiotics. This review will summarize research showing the significant role of EOs as nonconventional regimens against the worldwide spread of antibiotic-resistant pathogens. The authors conducted a 4-year search of the US National Library of Medicine (PubMed) for relevant EO studies against methicillin-resistant Staphylococcus aureus, multidrug-resistant (MDR) Escherichia coli, EO combinations/synergy with antibiotics, against MDR fungal infections, showing the ability to permeate bacterial membranes, and against the bacterial defenses listed above. EOs are readily available and are a needed addition to the arsenal against resistant pathogens.

Antibacterial Activity of Endostemon tereticaulis (Poir.) M. Ashby Essential Oil and Ethanolic Extract Against Resistant Pathogenic Bacteria

Endostemon tereticaulis (poir.) M.Ashby is a species of the Lamiaceae family present in Niger. This plant is used in traditional medicine due to its various biological potentialities. The present study investigated the chemical composition of the essential oil and the antibacterial activity of the essential oil and ethanolic extract of Endostemon tereticaulis against resistant pathogenic bacteria. Gas chromatography-mass spectrometry analysis of the essential oil led to the identification of 43 compounds representing 99.55% of the total essential oil. The major components were caryophyllene oxide (15.17%) followed by α-humulene (13.96%), α-copaene (11.75%), ( E)-β-caryophyllene (8.44%), and δ-cadinene (6.78%). The antibacterial activity was tested against multiresistant Acinetobacter baumannii P1483, Salmonella spp. H1548, extended-spectrum β-lactamase- Escherichia coli Bu8566, Enterobacter cloacae Bu147, Proteus mirabilis Bu190 , Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (ATCC 700603), Escherichia coli (ATCC 25922), Enterococcus faecium H3434, methicillin-resistant Staphylococcus aureus P1123, and Staphylococcus aureus (ATCC 25923). The antibacterial assays revealed that the essential oil was more active than the ethanolic extract against the studied bacteria with minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values ranging from 0.06 to 2 mg/mL. Also, the ethanolic extract was effective against the bacteria tested with MIC and MBC values ranging from 0.12 to 3 mg/mL. This study showed that Endostemon tereticaulis essential oil is rich in bioactive compounds. Ethanolic extract and essential oil exhibited potential antibacterial activity. These results provide a scientific basis for the use of this plant in traditional medicine. The current study described for the first time the antibacterial activity of Endostemon tereticaulis.

Anti-Acinetobacter baumannii activity of selected phytochemicals alone, in binary combinations and in combinations with conventional antibiotics

Acinetobacter baumannii is one of the emerging multidrug- and pandrug-resistant pathogens. The aim of the study was to determine anti-A. baumannii activity of selected terpenes, terpenoids and phenylpropanoids alone, in binary combinations, and in combinations with conventional antibiotics using microdilution-checkerboard and time-kill curve method. The most effective were terpenoids carvacrol (7.0-28.0 μg mL^-1) and thymol (22.0-76.0 μg mL^-1), as well as phenylpropanoid compound eugenol (90.5-304.0 μg mL^-1), with the active concentrations were comparable to antibiotics. The binary combinations showed additive or indifferent effects. The combination gentamicin-carvacrol was synergistic only against reference strain (FICI = 0.50), while other combinations were additive. The best bacteriostatic activity showed carvacrol, thymol or eugenol in combination with ciprofloxacin (FICI range 0.11-0.50) against both the reference and multidrug-resistant strains. The synergistic effect was further confirmed by time kill curve method and obtained after only 15 h. The results indicate a new possible therapeutic strategy against multiple resistant A. baumannii.

Selection of Optimal Operating Conditions for Extraction of Myrtus Communis L. Essential Oil by the Steam Distillation Method

Myrtus communis L. is one of the important aromatic and medicinal species from the Mediterranean area. It is used in various fields such as culinary, cosmetic, pharmaceutical, therapeutic, and industrial applications. Thus, a Box–Wilson experimental plan was used in this study to select the optimal operating conditions in order to obtain high volumes of essential oils. The factorial design method was applied to evaluate at an industrial scale the effect of major process variables on the essential oil extraction from Myrtus communis L. herbs by the steam distillation method. The input variables considered as significant operating conditions were: X₁—boiler occupancy rate (boilers were filled to 50%, 75%, and 100%), X₂—distillation duration (distillation was continued 60, 75, and 90 min), and X₃—particle size (herbs were cut in sizes of 10, 20, and 30 mm via guillotine). The dependent variable selected, coded as Y, was the essential oil volume obtained (mL). The steps of the classical statistical experimental design technique were complemented with the Taguchi method to improve the extraction efficacy of essential oil from Myrtus communis L., and the optimum parameter conditions were selected: boiler occupancy rate 100%, distillation duration 75 min, and particle size 20 mm. Following the optimum parameters, the GC-MS assay revealed for the Myrtus communis L. essential oil two predominant components, α-pinene—33.14% and eucalyptol—55.09%.

Analysis of Chemical Composition and Assessment of Antioxidant, Cytotoxic and Synergistic Antibacterial Activities of Essential Oils from Different Plant Parts of Piper boehmeriifolium

The essential oils (EOs) from leaves, stems, and whole plant of Piper boehmeriifolium were analyzed using GC/FID and GC/MS. The main constituents of P. boehmeriifolium EOs were β-caryophyllene, caryophyllene oxide, β-elemene, spathulenol, germacrene D, β-selinene, and neointermedeol. The antioxidant potential of the EOs were determined using DPPH^• , ABTS^•+ and FRAP assays. In ABTS^•+ assay, the leaf oil exhibited a remarkable activity with an IC₅₀ value of 7.36 μg/mL almost similar to BHT (4.06 μg/mL). Furthermore, the antibacterial activity of the oils as well as their synergistic potential with conventional antibiotics were evaluated using microdilution and Checkerboard assays. The results revealed that the oils from different parts of P. boehmeriifolium inhibited the growth of all tested bacteria and the minimum inhibitory concentrations were determined to be 0.078 - 1.250 mg/mL. In combination with chloramphenicol or streptomycin, the oils showed significant synergistic antibacterial effects in most cases. Besides, the results of MTT assay indicated that the oil of the whole plant exhibited significant cytotoxic activities on human hepatocellular carcinoma cells (HepG2) and human breast cancer cells (MCF-7). In summary, the P. boehmeriifolium oils could be regarded as a prospective source for pharmacologically active compounds.

Non-antibiotic antimicrobial interventions and antimicrobial stewardship in wound care

Control of wound infection today relies largely on antibiotics, but the continual emergence of antibiotic-resistant microorganisms threatens a return to the pre-antibiotic era when physicians used antiseptics to prevent and manage infection. Some of those antiseptics are still used today, and others have become available. A diverse variety of non-antibiotic antimicrobial interventions are found on modern formularies. Unlike the mode of action of antibiotics, which affect specific cellular target sites of pathogens, many non-antibiotic antimicrobials affect multiple cellular target sites in a non-specific way. Although this reduces the likelihood of selecting for resistant strains of microorganisms, some have emerged and cross-resistance between antibiotics and antiseptics has been detected. With the prospect of a post-antibiotic era looming, ways to maintain and extend our antimicrobial armamentarium must be found. In this narrative review, current and emerging non-antibiotic antimicrobial strategies will be considered and the need for antimicrobial stewardship in wound care will be explained.

Potential effect of 2-isopropyl-5-methylphenol (thymol) alone and in combination with fluconazole against clinical isolates of Candida albicans, C. glabrata and C. krusei

Limitations of antifungals used in the treatment of candidiasis, as the development of resistant strains, are known by the scientific community. In this context, the aim of this study was to investigate the activity of 2-isopropyl-5-methylphenol (thymol) in combination with fluconazole (FLZ) against clinical Candida strains. The antifungal activity of thymol along with FLZ was evaluated by the Clinical Laboratory Standards Institute (CLSI) M27-A2 broth microdilution method. In addition, synergism was observed for clinical strains of Candida spp. with combination of thymol-FLZ evaluated by the chequerboard microdilution method. The mean of minimum inhibitory concentration (MIC) values of thymol and FLZ were 49.37 and 0.475μg/ml for C. albicans, 51.25 and 18.80μg/ml for C. glabrata and 70 and 179.20μg/ml for C. krusei strains, respectively. Thymol in combination with FLZ exhibited the synergistic effects against all species of Candida tested. FICI values for thymol plus FLZ ranged from 0.366 to 0.607 for C. albicans strains, 0.367 to 0.482 for C. glabrata strains, and 0.375 to 0.563 for C. krusei strains. No antagonistic activity was seen in the strains tested. Thymol was found to have a fungicidal effect on Candida species and a synergistic effect when combined with FLZ.

Antibiotic resistance of pathogenic Acinetobacter species and emerging combination therapy

The increasing antibiotic resistance of Acinetobacter species in both natural and hospital environments has become a serious problem worldwide in recent decades. Because of both intrinsic and acquired antimicrobial resistance (AMR) against last-resort antibiotics such as carbapenems, novel therapeutics are urgently required to treat Acinetobacter-associated infectious diseases. Among the many pathogenic Acinetobacter species, A. baumannii has been reported to be resistant to all classes of antibiotics and contains many AMR genes, such as bla _ADC (Acinetobacter-derived cephalosporinase). The AMR of pathogenic Acinetobacter species is the result of several different mechanisms, including active efflux pumps, mutations in antibiotic targets, antibiotic modification, and low antibiotic membrane permeability. To overcome the limitations of existing drugs, combination theraphy that can increase the activity of antibiotics should be considered in the treatment of Acinetobacter infections. Understanding the molecular mechanisms behind Acinetobacter AMR resistance will provide vital information for drug development and therapeutic strategies using combination treatment. Here, we summarize the classic mechanisms of Acinetobacter AMR, along with newly-discovered genetic AMR factors and currently available antimicrobial adjuvants that can enhance drug efficacy in the treatment of A. baumannii infections.

Biological Activities of Essential Oils: From Plant Chemoecology to Traditional Healing Systems

Essential oils are complex mixtures of hydrocarbons and their oxygenated derivatives arising from two different isoprenoid pathways. Essential oils are produced by glandular trichomes and other secretory structures, specialized secretory tissues mainly diffused onto the surface of plant organs, particularly flowers and leaves, thus exerting a pivotal ecological role in plant. In addition, essential oils have been used, since ancient times, in many different traditional healing systems all over the world, because of their biological activities. Many preclinical studies have documented antimicrobial, antioxidant, anti-inflammatory and anticancer activities of essential oils in a number of cell and animal models, also elucidating their mechanism of action and pharmacological targets, though the paucity of in human studies limits the potential of essential oils as effective and safe phytotherapeutic agents. More well-designed clinical trials are needed in order to ascertain the real efficacy and safety of these plant products.

Myrtus communis L. and its application in treatment of Recurrent Aphthous Stomatitis

ETHNOPHARMACOLOGICAL RELEVANCE

In Iranian Traditional Medicine, M. communis is a famous plant in treatment of oral ulcers and "Gholaa"- the ancient name of aphthous.

OBJECTIVE

The aim of this review is to create a bridge between the traditional claims about the application of M. communis in treatment of "Gholaa" and its prescription for aphthous, the current form of "Gholaa" in modern medicine METHODS: We extracted the information about the application of M. communis in treatment of aphthous from different resources including Google scholar, Pubmed, ScienceDirect, Springer, ethnobotanical, the traditional books from Traditional Medicine Tehran University of Medical Sciences.

RESULTS

In Iranian traditional texts, "Gholaa" was the corrosive diseases on the surface and inner layer of mouth and tongue and divided into three types of bloody, phlegmatic and burned black bile types. Recurrent Aphthous Stomatitis (RAS) is equal to the black bile and phlegmatic types and minor aphthous type can be matched with phlegmatic type. The corrosive propagated lesions can be herpetic aphthous. In modern medicine, M. communis essential oil and its decoction decreased the average time of pain relief and decreased the size of ulcers in patients with minor RAS without any adverse effects. The number of ulcers was not the subjects of any different clinical trials. All patients were satisfied with M. communis topical essential oil (5%), and 81% patients were satisfied with M. communis topical decoctions (5%). It appears the efficacy of M. communis is related to its analgesic, anti-inflammatory, antiseptic and wound healing effects.

CONCLUSION

M. communis is effective in minor RAS as its traditional claims and confirming its efficacy in major and herpetiform RAS and comparing the efficacy of its decoction topical formulations or essential oil topical ones are required more and larger experimental and clinical investigations in future.

Reversal of resistance in bacteria underlies synergistic effect of essential oils with conventional antibiotics

The pervasive of bacterial resistance earnestly threaten the prevention and the treatment of infectious diseases. Therefore, scientific communities take precedence over development of new antimicrobial agents. The aim of the study was to determine antimicrobial potency of three North-African essential oils Pituranthos chloranthus, Teucruim ramosissimum and Pistacia lentiscus individually, and in combination with antibiotics, to inhibit the growth of highly resistant clinical pathogen. Bacteria clinically isolated from patients, subsequently, challenged to a panel of drugs to determine the antibiotic-resistance profiles. Drugs displaying clinically irrelevant CMI were subjected to further studies in order to rescue antibiotic actions. Singular activity of essential oils and activity when combined with an antibiotic was hence elucidated. The results obtained highlighted the occurrence of strong antibacterial potential of essential oils when administrated alone. In the interactive experiment essential oils were found highly effective in reducing the resistance of Methicillin-resistant Staphylococcus aureus to amoxicillin, tetracycline, piperacillin, ofloxacin and oxacillin and resistance of Acinetobacter baumannii to amoxicillin and to ofloxacin in interactive manner. Furthermore, the results proved synergism among essential oils and both antibiotics ofloxacin and novobiocin against the Extended-Spectrum Beta-Lactamase producing E. coli (ESBL). Time kill kinetics was performed with a combination of sub-inhibitory concentrations to confirm the efficiency and killing rate of the combination over time. Further, the hypothetical toxicity of essential oils against human keratinocytes HaCat and murine spleenocytes were examined. The chemical composition of essential oils was assessed by GC/MS analysis and the major constituents found were sabinene, limonene, terpinen-4-ol, and β-eudesmol.

Antimicrobial activity, cytotoxicity and chemical analysis of lemongrass essential oil (Cymbopogon flexuosus) and pure citral

The aim of this study was to determine the antimicrobial effects of lemongrass essential oil (C. flexuosus) and to determine cytotoxic effects of both test compounds on human dermal fibroblasts. Antimicrobial susceptibility screening was carried out using the disk diffusion method. Antimicrobial resistance was observed in four of five Acinetobacter baumannii strains with two strains confirmed as multi-drug-resistant (MDR). All the strains tested were susceptible to both lemongrass and citral with zones of inhibition varying between 17 to 80 mm. The mean minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of citral (mic—0.14 % and mbc—0.3 % v/v) was lower than that of Lemongrass (mic—0.65 % and mbc—1.1 % v/v) determined using the microtitre plate method. Cell viability using human dermal fibroblasts (HDF; 106-05a) was determined following exposure to both compounds and a control (Grapeseed oil) using the XTT assay and the IC₅₀ determined at 0.095 % (v/v) for citral and 0.126 % (v/v) for lemongrass. Grapeseed oil had no effect on cell viability. Live cell imaging was performed using the LumaScope 500 imaging equipment and changes in HDF cell morphology such as necrotic features and shrinkage were observed. The ability of lemongrass essential oil (EO) and citral to inhibit and kill MDR A. baumannii highlights its potential for use in the management of drug-resistant infections; however, in vitro cytotoxicity does suggest further tests are needed before in vivo or ex vivo human exposure.

Essential Oils and Their Components as Modulators of Antibiotic Activity against Gram-Negative Bacteria

Gram-negative bacteria cause infections that are difficult to treat due to the emergence of multidrug resistance. This review summarizes the current status of the studies investigating the capacity of essential oils and their components to modulate antibiotic activity against Gram-negative bacteria. Synergistic interactions are particularly discussed with reference to possible mechanisms by which essential oil constituents interact with antibiotics. Special emphasis is given to essential oils and volatile compounds that inhibit efflux pumps, thus reversing drug resistance in Gram-negative bacteria. In addition, indifference and antagonism between essential oils/volatile compounds and conventional antibiotics have also been reported. Overall, this literature review reveals that essential oils and their purified components enhance the efficacy of antibiotics against Gram-negative bacteria, being promising candidates for the development of new effective formulations against Gram-negative bacteria.

Chemometric investigation of light-shade effects on essential oil yield and morphology of Moroccan Myrtus communis L

Background

To investigate the effect of environmental factors such as light and shade on essential oil yield and morphological traits of Moroccan Myrtus communis, a chemometric study was conducted on 20 individuals growing under two contrasting light environments.

Results

The study of individual’s parameters by principal component analysis has shown that essential oil yield, altitude, and leaves thickness were positively correlated between them and negatively correlated with plants height, leaves length and leaves width. Principal component analysis and hierarchical cluster analysis have also shown that the individuals of each sampling site were grouped separately. The one-way ANOVA test has confirmed the effect of light and shade on essential oil yield and morphological parameters by showing a statistically significant difference between them from the shaded side to the sunny one. Finally, the multiple linear model containing main, interaction and quadratic terms was chosen for the modeling of essential oil yield in terms of morphological parameters.

Conclusions

Sun plants have a small height, small leaves length and width, but they are thicker and richer in essential oil than shade plants which have shown almost the opposite. The highlighted multiple linear model can be used to predict essential oil yield in the studied area.

Antimicrobial activity of Eucalyptus camaldulensis essential oils and their interactions with conventional antimicrobial agents against multi-drug resistant Acinetobacter baumannii

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional herbal medicine has become an important issue on the global scale during the past decade. Among drugs of natural origin, special place belongs to essential oils, known as strong antimicrobial agents that can be used to combat antibiotic-resistant bacteria. Eucalyptus camaldulensis leaves are traditional herbal remedy used for various purposes, including treatment of infections. The aim of this study was to determine antimicrobial potential of two E. camaldulensis essential oils against multi-drug resistant (MDR) Acinetobacter baumannii wound isolates and to examine possible interactions of essential oils with conventional antimicrobial agents.

MATERIALS AND METHODS

Chemical composition of essential oils was determined by gas chromatography-mass spectrometry analysis (GC-MS). MIC values of essential oils against A. baumannii strains were estimated by modified broth microdilution method. The components responsible for antimicrobial activity were detected by bioautographic analysis. The potential synergy between the essential oils and antibiotics (ciprofloxacin, gentamicin and polymyxin B) was examined by checkerboard method and time kill curve.

RESULTS

The dominant components of both essential oils were spatulenol, cryptone, p-cimene, 1,8-cineole, terpinen-4-ol and β-pinene. The detected MICs for the E. camaldulensis essential oils were in range from 0.5 to 2 μl mL(-1). The bioautographic assay confirmed antibacterial activity of polar terpene compounds. In combination with conventional antibiotics (ciprofloxacin, gentamicin and polymyxin B), the examined essential oils showed synergistic antibacterial effect in most of the cases, while in some even re-sensitized MDR A. baumannii strains. The synergistic interaction was confirmed by time-kill curves for E. camaldulensis essential oil and polymyxin B combination which reduced bacterial count under detection limit very fast, i.e. after 6h of incubation.

CONCLUSIONS

The detected anti-A. baumannii activity of E. camaldulensis essential oils justifies traditional use of this plant. The proven E. camaldulensis essential oil synergistic interactions with conventional antibiotics could lead to the development of new treatment strategies of infections caused by MDR A. baumannii strains in the term of antibiotic dose reduction.

Antifungal activity and mode of action of thymol and its synergism with nystatin against Candida species involved with infections in the oral cavity: an in vitro study

BACKGROUND

Limitations of antifungal agents used in the treatment of oral candidiasis, as the development of resistant strains, are known by the scientific community. In this context, the aim of this study was to evaluate the antifungal activity of thymol against Candida albicans, Candida tropicalis and Candida krusei strains and to determine its mode of action and synergistic effect when combined with the synthetic antifungal nystatin.

METHODS

The minimum inhibitory concentration (MIC) was determined using a microdilution technique, and the minimum fungicidal concentration (MFC) was determined via subculture sowing. The mode of action of thymol was established by verifying fungal growth in the presence of sorbitol or ergosterol. The fractional inhibitory concentration index (FIC) was determined using the checkerboard method.

RESULTS

Thymol presented an antifungal effect, with MICs of 39 μg/mL for C. albicans and C. krusei and 78 μg/mL for C. tropicalis. The results of the antifungal test remained unchanged in the presence of sorbitol; however, the MIC value of thymol against C. albicans increased eight times (from 39.0 to 312.5 μg/mL) in presence of exogenous ergosterol. The combination of thymol and nystatin reduced the MIC values of both products by 87.4%, generating an FIC index of 0.25.

CONCLUSIONS

Thymol was found to have a fungicidal effect on Candida species and a synergistic effect when combined with nystatin.