椒样薄荷、薄荷和苏格兰留兰香精油与抗生素的协同抑菌功能

以开花期的椒样薄荷(Mentha × piperita)、薄荷(M. haplocalyx)和苏格兰留兰香(M. × gentilis)叶片部位提取的精油为研究对象, 通过GC-MS分析, 并采用纸片扩散法研究了3种精油单独使用及与抗生素联合使用时对金黄色葡萄球菌、蜡状芽孢杆菌、大肠杆菌、绿脓杆菌和肺炎克雷伯氏菌的抑制情况。结果表明, (1) 椒样薄荷与薄荷精油中含量最高的成分为薄荷醇、薄荷酮和异薄荷酮, 苏格兰留兰香精油的主要成分为香芹酮和柠檬烯。薄荷和苏格兰留兰香精油符合欧洲药典与ISO标准, 椒样薄荷需要继续改良以提高其精油品质与抑菌功能。(2) 精油单独使用时, Pseudomonas aeruginosa ATCC 15442对椒样薄荷精油和薄荷精油敏感; P. aeruginosa ATCC 27853对薄荷精油和苏格兰留兰香精油敏感。精油与抗生素联合使用时抑菌范围和强度均有所改变: 绿脓杆菌的2个菌株对精油与抗生素的组合最为敏感, 其中, 椒样薄荷精油与头孢他啶的组合对P. aeruginosa ATCC 15442显示出最强的增效作用, 薄荷精油与头孢他啶混合之后对P. aeruginosa ATCC 27853出现拮抗作用。Staphylococcus aureus ATCC 25923对所有精油以及精油与抗生素混合物均有抗性。(3) 椒样薄荷、薄荷和苏格兰留兰香精油的不同成分及其含量差异不仅对精油品质有影响, 而且影响精油对测试菌种的抑制作用, 可考虑将其作为薄荷属植物品质育种的参考指标。     

椒样薄荷、薄荷和苏格兰留兰香精油与抗生素的协同抑菌功能

以开花期的椒样薄荷（Mentha×piperita）、薄荷（M.haplocalyx）和苏格兰留兰香（M.×gentilis）叶片部位提取的精油为研究对象,通过GC-MS分析,并采用纸片扩散法研究了3种精油单独使用及与抗生素联合使用时对金黄色葡萄球菌、蜡状芽孢杆菌、大肠杆菌、绿脓杆菌和肺炎克雷伯氏菌的抑制情况。结果表明,（1）椒样薄荷与薄荷精油中含量最高的成分为薄荷醇、薄荷酮和异薄荷酮,苏格兰留兰香精油的主要成分为香芹酮和柠檬烯。薄荷和苏格兰留兰香精油符合欧洲药典与ISO标准,椒样薄荷需要继续改良以提高其精油品质与抑菌功能。（2）精油单独使用时,Pseudomonas aeruginosa ATCC15442对椒样薄荷精油和薄荷精油敏感;P.aeruginosa ATCC27853对薄荷精油和苏格兰留兰香精油敏感。精油与抗生素联合使用时抑菌范围和强度均有所改变：绿脓杆菌的2个菌株对精油与抗生素的组合最为敏感,其中,椒样薄荷精油与头孢他啶的组合对P.aeruginosa ATCC15442显示出最强的增效作用,薄荷精油与头孢他啶混合之后对P.aeruginosa ATCC27853出现拮抗作用。Staphylococcus aureus ATCC25923对所有精油以及精油与抗生素混合物均有抗性。（3）椒样薄荷、薄荷和苏格兰留兰香精油的不同成分及其含量差异不仅对精油品质有影响,而且影响精油对测试菌种的抑制作用,可考虑将其作为薄荷属植物品质育种的参考指标。     

Control of Aspergillus section Flavi growth and aflatoxin accumulation by plant essential oils

Aims:  The antifungal effect of Pimpinella anisum (anise), Pëumus boldus (boldus), Mentha piperita (peppermint), Origanum vulgare (oregano) and Minthosthachys verticillata (peperina) essential oils against Aspergillus section Flavi (two isolates of Aspergillus parasiticus and two isolates of Aspergillus flavus ) was evaluated in maize meal extract agar at 0·982 and 0·955 water activities, at 25°C.
Methods and Results:  The percentage of germination, germ-tube elongation rate, growth rate and aflatoxin B₁ (AFB₁) accumulation at different essential oils concentrations were evaluated. Anise and boldus essential oils were the most inhibitory at 500 mg kg⁻¹ to all growth parameters of the fungus. These essential oils inhibited the percentage of germination, germ-tube elongation rate and fungal growth. AFB₁ accumulation was completely inhibited by anise, boldus and oregano essential oils. Peperina and peppermint essential oils inhibited AFB₁ production by 85–90% in all concentrations assayed.
Conclusions:  Anise and boldus essential oils could be considered as effective fungitoxicans for Aspergillus section flavi .
Significance and Impact of the Study:  Our results suggest that these phytochemical compounds could be used alone or in conjunction with other substances to control the presence of aflatoxigenic fungi in stored maize.     

The in vitro antibiofilm activity of selected culinary herbs and medicinal plants against Listeria monocytogenes

Aims:  The antibiofilm activity of extracts obtained from selected herbs, spices, beverages and commercially important medicinal plants was investigated on Listeria monocytogenes .
Methods and Results:  The growth and development of the biofilm was assessed using the crystal violet (CV) assay. The respiratory activity was assessed using the 2, 3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) reduction assay. The majority of extracts tested prevented cell adhesion to the polyvinyl chloride (PVC) surface. Seven of the 15 extracts reduced biofilm adhesion of both the clinical and the type strains by at least 50%. In contrast, inhibition of a preformed biofilm was more difficult to achieve, with only three extracts ( Rosmarinus officinalis, Mentha piperita and Melaleuca alternifolia ) inhibiting the growth of both strains by at least 50%.
Conclusions:  Although most extracts were able to reduce initial cell attachment, inhibition of growth in a preformed biofilm was more difficult to achieve.
Significance and Impact of the Study:  The ability to reduce biofilm biomass as shown by several plant extracts warrants further investigation to explore the use of natural products in antibiofilm adhesion.     

Comparison of bacteriostatic and bactericidal activity of 13 essential oils against strains with varying sensitivity to antibiotics

Aims:  To compare the bacteriostatic and bactericidal activity of 13 chemotyped essential oils (EO) on 65 bacteria with varying sensitivity to antibiotics.
Methods and Results:  Fifty-five bacterial strains were tested with two methods used for evaluation of antimicrobial activity (CLSI recommendations): the agar dilution method and the time-killing curve method. EO containing aldehydes ( Cinnamomum verum bark and Cymbopogon citratus ), phenols ( Origanum compactum , Trachyspermum ammi , Thymus satureioides , Eugenia caryophyllus and Cinnamomum verum leaf) showed the highest antimicrobial activity with minimum inhibitory concentration (MIC) <2% (v/v) against all strains except Pseudomonas aeruginosa . Alcohol-based EO ( Melaleuca alternifolia , Cymbopogon martinii and Lavandula angustifolia ) exhibited varying degrees of activity depending on Gram status. EO containing 1·8-cineole and hydrocarbons ( Eucalyptus globulus , Melaleuca cajeputii and Citrus sinensis ) had MIC_90% ≥ 10% (v/v). Against P. aeruginosa , only C. verum bark and O. compactum presented MIC ≤2% (v/v). Cinnamomum verum bark, O. compactum , T. satureioides , C. verum leaf and M. alternifolia were bactericidal against Staphylococcus aureus and Escherichia coli at concentrations ranging from to 0·31% to 10% (v/v) after 1 h of contact. Cinnamomum verum bark and O. compactum were bactericidal against P. aeruginosa within 5 min at concentrations <2% (v/v).
Conclusions:  Cinnamomum verum bark had the highest antimicrobial activity, particularly against resistant strains.
Significance and Impact of the Study:  Bacteriostatic and bactericidal activity of EO on nosocomial antibiotic-resistant strains.     

In Vitro Synergistic Activities of Essential Oils and Surfactants in Combination with Cosmetic Preservatives Against Pseudomonas aeruginosa and Staphylococcus aureus

The aim of this study is to evaluate possible synergistic antimicrobial interactions between common cosmetic preservatives and selected essential oils or surfactants. The antimicrobial efficacy of six essential oils, three surfactants and five preservatives against Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 43387 was assessed by a broth micro-dilution assay. MICs for individual and combined antimicrobials were determined and then transformed to fractional inhibitory concentration (FIC) indexes. All essential oils exhibited antibacterial activity; among surfactants, bacteria resulted most susceptible to the cationic agent. Synergy was observed when essential oils of eucalyptus and mint were combined with methylparaben against P. aeruginosa, while essential oils of mint, oregano and sage combined with propylparaben and imidazolidinyl urea acted against S. aureus. Many binary mixtures of preservatives and surfactants produced synergistic activity with the most effective interactions involving the cationic and amphoteric compounds under study. FIC indexes demonstrated synergistic effects when preservatives were combined with either essential oils or surfactants against both bacterial strains. These results highlight the potential usefulness of essential oils and surfactants to enhance the activities of conventional biocides. This kind of study should contribute to the selection and optimization of preservative systems for cosmetic preparations.     

Effects of Antifungal Agents Alone and in Combination Against Candida glabrata Strains Susceptible or Resistant to Fluconazole

The rise of Candida spp. resistant to classic triazole antifungal agents has led to a search for new therapeutic options. Here, we evaluated combinations of antifungals in a checkerboard assay against two groups of Candida glabrata strains: one containing fluconazole-susceptible clinical isolates (FS) and another containing fluconazole-resistant laboratory derivative (FR). The most synergistic combination observed was amphotericin B + flucytosine (synergistic for 61.77 % of FS strains and 76.47 % of FR strains). The most antagonistic combination observed was ketoconazole + flucytosine (FS 61.77 % and FR 55.88 %). Surprisingly, most combinations evidenced indifferent interactions, and the best synergism appeared when amphotericin B and flucytosine were combined against both groups of isolates.     

Effectiveness of cell-adsorbed bacteriocin produced by Lactobacillus curvatus CWBI-B28 and selected essential oils to control Listeria monocytogenes in pork meat during cold storage

Aims:  To study the effectiveness of a combination of cell-adsorbed bacteriocin (CAB; a suspension of producer cells on which maximum bacteriocin has been immobilized by pH adjustments) of a Lactobacillus curvatus strain with oregano or savory essential oil to control Listeria monocytogenes in pork meat at 4°C.
Methods and Results:  The antimicrobial activity of the CAB and six different essential oils was tested by the well diffusion assay against L. monocytogenes M, Escherichia coli 10536 and Salmonella serotype Typhi CWBI-H1. The anti- Listeria activity of the CAB and oregano or savory essential oils was also investigated in pork meat. The results of the well diffusion assay showed that CAB was only inhibitory to L. monocytogenes while savory and oregano essential oils were the most active against the three indicator bacteria. In pork meat, Listeria counts have declined from c. 10² CFU g⁻¹ to below the detectable limit during the first week of storage in samples treated with CAB or oregano essential oil and in those treated with CAB combined with oregano or savory essential oil. However, the counts of L. monocytogenes have increased after the third week of storage in all samples with the exception of those treated with the combination of CAB and oregano essential oil. The combination of CAB with savory essential oil resulted in a 2-week delay of the growth rebound compared with samples treated with CAB alone.
Conclusions:  Addition of oregano or savory essential oil exhibited a synergistic effect with CAB to control L. monocytogenes in pork meat during storage at 4°C.
Significance and Impact of the Study:  The combination of CAB with oregano or savory essential oil may be effectively used in meat industry to enhance the safety and stability of meat products.     

Validating the in vitro antimicrobial activity of Artemisia afra in polyherbal combinations to treat respiratory infections

Artemisia afra is one of the most widely used medicinal plants in African traditional medicine and is commonly administered in polyherbal combinations to treat respiratory infections. Focussing on plant volatiles, the aim of this study was to provide scientific evidence for the antimicrobial activity of A. afra (principle plant) in combination with essential oils from three medicinal aromatic plants; Agathosma betulina, Eucalyptus globulus and Osmitopsis asteriscoides. In vitro minimum inhibitory concentration (MIC) assays were undertaken on four pathogens (Enterococcus faecalis ATCC 29212, Moraxella catarrhalis ATCC 23246, Klebsiella pneumoniae NCTC 9633 and Cryptococcus neoformans ATCC 90112) to determine antimicrobial efficacy of the oils and their combinations. The fractional inhibitory concentration (FIC) and isobolograms were used to interpret pharmacodynamic interactions such as synergy, antagonism or additive profiles. The antimicrobial activity of the individual oils mostly displayed moderate activity. Predominantly, additive interactions were noted. The most prominent synergistic interaction (FIC value of 0.5) was observed when A. afra was combined with O. asteriscoides in the 8:2 ratio (eight parts A. afra with two parts O. asteriscoides) against C. neoformans. No antagonistic interactions were evident.     

Synergistic interactions between cefalexin and kanamycin in Mueller–Hinton broth medium and in milk

Aims:  This study investigated the in vitro bactericidal activity of an intramammary drug product by comparing the kill kinetics of cefalexin and kanamycin, alone and in fixed ratio combination, against Streptococcus uberis , Staphylococcus aureus and Escherichia coli strains isolated from field cases of bovine mastitis. The effect of milk as a diluent on the rate of bacterial killing was also assessed.
Methods and Results:  Antibacterial kill kinetics was determined against each bacterial strain in Mueller–Hinton broth (MHB) and in milk. In MHB, the fixed cefalexin : kanamycin combination (1·5 : 1 w/w) exhibited a clear synergistic bactericidal activity against the strains tested. The combination also showed an enhanced killing activity in milk, as compared to either agent alone.
Conclusions:  The data show the occurrence of synergistic interactions between cefalexin and kanamycin, resulting in a faster and enhanced bactericidal activity against major mastitis pathogens.
Significance and Impact of the Study:  The study demonstrated that the combination exhibited a larger and faster rate of kill of S. aureus , S. uberis and E. coli compared to either cefalexin or kanamycin alone, while using a lower total amount of antibiotic. Synergistic and additive effects were also observed when milk was used as a medium. The results support the use of this combination of narrow spectrum antibiotics to treat clinical mastitis via the intramammary route and provide data on its killing kinetics.     

Fumigant toxicity of plant essential oils against Camptomyia corticalis (Diptera: Cecidomyiidae)

The toxicity of 98 plant essential oils against third instars of cecidomyiid gall midge Camptomyia corticalis (Loew) (Diptera: Cecidomyiidae) was examined using a vapor-phase mortality bioassay. Results were compared with that of a conventional insecticide dichlorvos. Based on 24-h LC50 values, all essential oils were less toxic than dichlorvos (LC50, 0.027 mg/cm3). The LC50 of caraway (Carum carvi L.) seed, armoise (Artemisia vulgaris L.), clary sage (Salvia sclarea L.), oregano (Origanum vulgare L.), lemongrass [Cymbopogon citratus (DC.) Stapf], niaouli (Melaleuca viridiflora Gaertner), spearmint (Mentha spicata L.), cassia especial (Cinnamomum cassia Nees ex Blume), Dalmatian sage (Salvia offcinalis L.), red thyme (Thymus vulgaris L.), bay [Pimenta racemosa (P. Mill.) J.W. Moore], garlic (Allium sativum L.), and pennyroyal (Mentha pulegium L.) oils is between 0.55 and 0.60 mg/cm3. The LC50 of cassia (C. cassia, pure and redistilled), white thyme (T. vulgaris), star anise (Illicium verum Hook.f.), peppermint (Mentha X piperita L.), wintergreen (Gaultheria procumbens L.), cinnamon (Cinnamomum zeylanicum Blume) bark, sweet marjoram (Origanum majorana L.), Roman chamomile [Chamaemelum nobile (L.) All.], eucalyptus (Eucalyptus globulus Labill.), rosemary (Rosmarinus officinalis L.),Virginian cedarwood (Juniperus virginiana L.), pimento berry [Pimenta dioica (L.) Merr.], summer savory (Satureja hortensis L.), lavender (Lavandula angustifolia Mill.), and coriander (Coriandrum sativum L.) oils is between 0.61 and 0.99 mg/cm3. All other essential oils tested exhibited low toxicity to the cecidomyiid larvae (LC50, >0.99 mg/cm3). Global efforts to reduce the level of highly toxic synthetic insecticides in the agricultural environment justify further studies on the active essential oils as potential larvicides for the control of C. corticalis populations as fumigants with contact action.     

The additive and synergistic antimicrobial effects of select frankincense and myrrh oils--a combination from the pharaonic pharmacopoeia

Aims: The in vitro antimicrobial activity of three essential oil samples of frankincense (Boswellia rivae, Boswellia neglecta and Boswellia papyrifera) and two essential oil samples of myrrh and sweet myrrh (Commiphora guidotti and Commiphora myrrha), collected from different regions of Ethiopia, was investigated independently and in combination to determine their anti‐infective properties. Methods and Results: The microdilution minimum inhibitory concentration (MIC) assay was performed, whereby it was noted that generally Cryptococcus neoformans (MIC values in the range of 0·8–1·4 mg ml^?1) and Pseudomonas aeruginosa (MIC values in the range of 0·5–1·3 mg ml^?1) often appeared to be the most susceptible micro‐organisms against oils of both Boswellia and Commiphora spp. When assayed in various combinations, the frankincense and myrrh oils displayed synergistic, additive and noninteractive properties, with no antagonism noted. When investigating different ratio combinations against Bacillus cereus, the most favourable combination was between B. papyrifera and C. myrrha. The composition of the oils was determined by gas chromatography coupled to mass spectrometry (GC–MS) to document the specific chemotypes used in the study, and the chemical profiles were found to be congruent with previously reported data. Conclusions: The majority of interactions identified synergistic and additive effects, with strong synergism noted between B. papyrifera and C. myrrha. Significance and Impact of the Study: Frankincense and myrrh essential oils have been used in combination since 1500 bc ; however, no antimicrobial investigations have been undertaken to confirm their effect in combination. This study validates the enhanced efficacy when used in combination against a selection of pathogens.     

Synergistic activity of 1-(1-naphthylmethyl)-piperazine with ciprofloxacin against clinically resistant Staphylococcus aureus, as determined by different methods

Aims: To evaluate the interaction of 1‐(1‐naphthylmethyl)‐piperazine (NMP) and ciprofloxacin (CPFX) in vitro against fluoroquinolone (FQ)‐resistant clinical isolates of methicillin‐resistant Staphylococcus aureus (MRSA). Methods and Results: The in vitro interaction of NMP and CPFX in 12 FQ‐resistant clinical isolates of MRSA was assessed using a checkerboard microdilution method. In the study, a synergistic antimicrobial effect between NMP and CPFX was observed in all 12 FQ‐resistant strains tested, as determined by the fractional inhibitory concentration index (FICI), and in 10 strains using ΔE models. No antagonistic activity was observed in any of the strains tested. These positive interactions were also confirmed using the time–killing test and agar diffusion assay for the selected strain, MRSA 1862; synergistic activity was observed when NMP was combined with the first‐line antimicrobial agent CPFX against Staph. aureus. Conclusions: Synergistic activity between NMP and CPFX against clinical isolates of FQ‐resistant Staph. aureus was observed in vitro. Significance and Impact of the Study: This report might provide alternative methods to reduce the resistance of Staph. aureus to CPFX.     

Antimicrobial activity of essential oils and structurally related synthetic food additives towards Clostridium perfringens

Aims:  To assess the potential of essential oils and structurally related synthetic food additives in inhibiting the growth of Clostridium perfringens for the control of necrotic enteritis in chickens.
Methods and Results:  The antimicrobial activity of essential oils/compounds was measured by determining the inhibition of bacterial growth. Thirty-three of 66 oils/compounds exhibited ≥80% inhibition. Seven with the highest potency were further studied. The oils/compounds had MIC₉₅ values between 167 and 425  μ g ml⁻¹. Most of them were tolerant to low pH (2·0) and exhibited minor or no inhibition of Lactobacillus isolates from the chicken intestine. When mixed with chicken ileal digesta, the oils/compounds retained their efficacy against C . perfringens , but had little effect on the total number of lactobacilli and anaerobic bacteria in the digesta.
Conclusions:  Some essential oils/compounds demonstrated good potential in controlling C . perfringens .
Significance and Impact of the Study:  This study has identified candidates of essential oils/compounds for in vivo studies for the control of necrotic enteritis in chickens.     

In vivo Evaluation of Essential Oils and Biocontrol Agents Combined with Hot Water Treatments on Carrot Seeds Against Alternaria radicina

Seed‐dressing with essential oils from aromatic plants (savoury and thyme) and with antagonistic bacteria strains (Pseudomonas spp.) was tested after a hot water treatment against Alternaria radicina inoculated on carrot seeds. Seed treatments by immersion in water at 55°C for 10 min improved the efficacy on pathogen control of the treatments with biocontrol agent strains more than the efficacy of those with essential oils. Pretreatment with hot water also increased the germination rate of carrot seeds. A mild phytotoxic effect was observed on the germination rate and the fresh biomass obtained from seeds treated with both essential oils. Treatments with essential oils and antagonistic bacteria presented positive results when combined with hot water dipping of seeds on control of A. radicina, but the effect was not completely additive. The formulation and the application method of the non‐chemical products tested are critical on their development as an alternative strategy on seed disinfection.     

Biochemical activities of Iranian Mentha piperita L. and Myrtus communis L. essential oils

GC-MS analysis of essential oils of Iranian Mentha piperita and Myrtus communis extracted by hydrodistillation lead to identification of 26 and 32 compounds, respectively. The oils had good to excellent antimicrobial activities against Escherichia coli, Staphylococcus aureus and Candida albicans with the oil of M. piperita being more active. The findings suggest feasibility of application of M. piperita oil in treatment of the infections caused by C. albicans and E. coli. D-values on exposure to M. piperita and Myrtus communis oils were (2.14 and 2.8min), (1.4 and 12.8min) and (4.3 and 8.6min) for E. coli, S. aureus and C. albicans , respectively. The oils were screened for their possible antioxidant activities by two complementary test systems, namely DPPH free radical scavenging and beta-carotene/linoleic acid systems. M. piperirta oil exerted greater antioxidant activity than that of M. communis. Phytochemical and phytobiological characteristics of these oils may lead to extraction and production of active compounds in single or combined forms with useful applications.     

Essential Oils as Potent Source of Nematicidal Compounds

Bioassay tests were conducted to find out the nematicidal activity of eight essential oils against Meloidogyne incognita (Kofoid and White) Chitwood at four concentrations. Maximum activity was recorded in oils of Eucalyptus citriodora , Eucalyptus hybrida and Ocimum basilicum followed by Pelargonium graveolens , Cymbopogon martinii, Mentha arvensis, Mentha piperita and Mentha spicata oils, respectively. The eucalyptus ( E. citriodora and E. hybrida ) and Indian basil ( O. basilicum ) oils were highly toxic to M. incognita even at the lower concentrations, namely 500 and 250 ppm. The remaining oils were also toxic to the nematode but at different amounts.     

Inhibition of quorum sensing regulated bacterial functions by plant essential oils with special reference to clove oil

Aims:  To evaluate quorum sensing (QS) inhibitory activity of plant essential oils using strains of Chromobacterium violaceum (CV12472 and CVO26) and Pseudomonas aeruginosa (PAO1).
Methods and Results:  Inhibition of QS-controlled violacein production in C. violaceum was assayed using disc diffusion and agar well diffusion method. Of the 21 essential oils, four oils showed varying levels of anti-QS activity. Syzygium aromaticum (Clove) oil showed promising anti-QS activity on both wild and mutant strains with zones of pigment inhibition 19 and 17 mm, respectively, followed by activity in cinnamon, lavender and peppermint oils. The effect of clove oil on the extent of violacein production was estimated photometrically and found to be concentration dependent. At sub-MICs of clove oil, 78·4% reduction in violacein production over control and up to 78% reduction in swarming motility in PAO1 over control were recorded. Gas chromatography–mass spectrometry analysis of clove oil indicated presence of many phytocompounds. Eugenol, the major constituent of clove oil could not exhibit anti-QS activity.
Conclusions:  Presence of anti-QS activity in clove oil and other essential oils has indicated new anti-infective activity. The identification of anti-QS phytoconstituents is needed to assess the mechanism of action against both C. violaceum and Ps. aeruginosa .
Significance and Impact of the study:  Essential oils having new antipathogenic drugs principle because of its anti-QS activity might be important in reducing virulence and pathogenicity of drug-resistant bacteria in vivo .     

Enhanced activity of antifungal drugs using natural phenolics against yeast strains of Candida and Cryptococcus

Aims: Determine whether certain, natural phenolic compounds enhance activity of commercial antifungal drugs against yeast strains of Candida and Cryptococcus neoformans. Methods and Results: Twelve natural phenolics were examined for fungicidal activity against nine reference strains of Candida and one of C. neoformans. Six compounds were selected for synergistic enhancement of antifungal drugs, amphotericin B (AMB), fluconazole (FLU) and itraconazole (ITR). Matrix assays of phenolic and drug combinations conducted against one reference strain, each, of Candida albicans and C. neoformans showed cinnamic and benzoic acids, thymol, and 2,3‐ and 2,5‐dihydroxybenzaldehydes (‐DBA) had synergistic interactions depending upon drug and yeast strain. 2,5‐DBA was synergistic with almost all drug and strain combinations. Thymol was synergistic with all drugs against Ca. albicans and with AMB in C. neoformans. Combinations of benzoic acid or thymol with ITR showed highest synergistic activity. Of 36 combinations of natural product and drug tested, none were antagonistic. Conclusions: Relatively nontoxic natural products can synergistically enhance antifungal drug activity, in vitro. Significance and Impact of the Study: This is a proof‐of‐concept, having clinical implications. Natural chemosensitizing agents could lower dosages needed for effective chemotherapy of invasive mycoses. Further studies against clinical yeast strains and use of animal models are warranted.     

In vitro activity of essential oils extracted from plants used as spices against fluconazole-resistant and fluconazole-susceptible Candida spp

In the present study, the antifungal activity of selected essential oils obtained from plants used as spices was evaluated against both fluconazole-resistant and fluconazole-susceptible Candida spp. The Candida species studied were Candida albicans, Candida dubliniensis, Candida tropicalis, Candida glabrata, and Candida krusei. For comparison purposes, they were arranged in groups as C. albicans, C. dubliniensis, and Candida non-albicans. The essential oils were obtained from Cinnamomum zeylanicum Breyn, Lippia graveolens HBK, Ocimum basilicum L., Origanum vulgare L., Rosmarinus officinalis L., Salvia officinalis L., Thymus vulgaris L., and Zingiber officinale. The susceptibility tests were based on the M27-A2 methodology. The chemical composition of the essential oils was obtained by gas chromatography-mass spectroscopy and by retention indices. The results showed that cinnamon, Mexican oregano, oregano, thyme, and ginger essential oils have different levels of antifungal activity. Oregano and ginger essential oils were found to be the most and the least efficient, respectively. The main finding was that the susceptibilities of fluconazole-resistant C. albicans, C. dubliniensis, and Candida non-albicans to Mexican oregano, oregano, thyme, and ginger essential oils were higher than those of the fluconazole-susceptible yeasts (P<0.05). In contrast, fluconazole-resistant C. albicans and Candida non-albicans were less susceptible to cinnamon essential oil than their fluconazole-susceptible counterparts (P<0.05). A relationship between the yeasts' susceptibilities and the chemical composition of the essential oils studied was apparent when these 2 parameters were compared. Finally, basil, rosemary, and sage essential oils did not show antifungal activity against Candida isolates at the tested concentrations.