A vapour phase assay for evaluating the antimicrobial activities of essential oils against bovine respiratory bacterial pathogens

Antimycobacterial potential of Trachyspermum ammi seed essential oil via fume contact and determination of major compounds

Trachyspermum ammi (L.), commonly known as carrom seeds or Ajwain, has been extensively studied for its medicinal properties. In this study, anti-mycobacterial effect of AEO in liquid and fume form was investigated against Mycobacterium smegmatis and Mycobacterium tuberculosis (M. tb). Results showed that AEO inhibits the growth of M. smegmatis at 0.03 mg/mL and becomes bactericidal at 0.125 mg/mL. MICs were observed at 0.03, 0.125 and 0.06 mg/mL against M. tb (H37Rv), isoniazid- and rifampicin-resistant (RIF-R) strains. Inverted disc-fume assay revealed AEO and Thymol efficiently inhibit the growth of M. smegmatis and M. tb. Similarly, in fume contact AEO and Thymol demonstrated antibiofilm activity at a dose of 1.25 mg/mL air and 40 mg/mL air against M.smegmatis effectively. GC-MS analysis showed that Thymol was the dominant compound. These findings suggest that the use of AEO in fume form may serve as a promising strategy as an anti-mycobacterial activity against M. tb.

A single intranasal dose of essential oil spray confers modulation of the nasopharyngeal microbiota and short-term inhibition of Mannheimia in feedlot cattle: a pilot study

Five essential oils (EOs) were previously characterized in vitro and identified as candidate EOs for the development of an intranasal EO spray to mitigate bovine respiratory disease (BRD) pathogens. In the present study, these EOs were evaluated for their potential to (i) reduce BRD pathogens, (ii) modulate nasopharyngeal microbiota, and (iii) influence animal performance, feeding behavior and immune response when a single dose administered intranasally to feedlot cattle. Forty beef steer calves (7-8 months old, Initial body weight = 284 ± 5 kg [SE]) received either an intranasal EO spray (ajowan, thyme, fennel, cinnamon leaf, and citronella) or PBS (Control; n = 20/group) on day 0. Deep nasopharyngeal swabs were collected on days (d) -1, 1, 2, 7, 14, 28, and 42 and processed for 16S rRNA gene sequencing, qPCR, and culturing. Significant effects of EO on community structure (d1), microbial richness and diversity, relative abundance of some dominant phyla (d1, d2, and d14), and the overall interaction network structure of the nasopharyngeal microbiota were detected. The relative abundance of Mannheimia was lower in the EO calves (4.34%) than in Control calves (10.4%) on d2, and M. haemolytica prevalence on d7 as compared to control calves. Feed intake, average daily gain, feeding behavior, and blood cell counts were not affected by EO treatment. Overall, a single intranasal dose of EO spray resulted in moderate modulation of nasopharyngeal microbiota and short-term inhibition of Mannheimia while not influencing animal performance, feeding behavior or immune response. Our study, for the first time, shows the potential use of intranasal EO to mitigate BRD in feedlot cattle.

Validation of Broth Macrodilution Volatilization Method for Testing of Essential Oils in Liquid and Vapor Phase: Chemical Composition, Cytotoxicity, and Antibacterial Effect of Indian Medicinal Plants against Pneumonia-Causing Pathogens

Essential oils (EOs) have great potential in inhalation therapy for the treatment of respiratory infections. However, innovative methods for evaluation of antimicrobial activity of their vapors are still needed. The current study reports validation of the broth macrodilution volatilization method for assessment of the antibacterial properties of EOs and shows the growth-inhibitory effect of Indian medicinal plants against pneumonia-causing bacteria in liquid and vapor phase. Among all samples tested, Trachyspermum ammi EO exhibits the strongest antibacterial effect against Haemophilus influenzae, with minimum inhibitory concentrations of 128 and 256 µg/mL in the liquid and vapor phases, respectively. Furthermore, Cyperus scariosus EO is found to be nontoxic to normal lung fibroblasts assessed by modified thiazolyl blue tetrazolium bromide assay. Chemical analysis performed using gas chromatography-mass spectrometry identified α-citral, cyperotundone, and thymol as the main constituents of Cymbopogon citratus, C. scariosus, and T. ammi EOs, respectively. In addition, β-cymene is identified as the major compound of T. ammi EO vapors when analyzed using solid-phase microextraction and gas-tight syringe sampling techniques. This study demonstrates the validity of the broth macrodilution volatilization method for antimicrobial screening of volatile compounds in the vapor phase and suggests the therapeutic potential of Indian medicinal plants in inhalation therapy.

Chemical Composition and Antibacterial Activity of Liquid and Volatile Phase of Essential Oils against Planktonic and Biofilm-Forming Cells of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen causing life-threatening, hard-to-heal infections associated with the presence of a biofilm. Essential oils (EOs) are promising agents to combat pseudomonal infections because of the alleged antimicrobial activity of their volatile fractions and liquid forms. Therefore, the purpose of this paper was to evaluate the antibacterial efficacy of both volatile and liquid phases of seven EOs (thyme, tea tree, basil, rosemary, eucalyptus, menthol mint, lavender) against P. aeruginosa biofilm and planktonic cells with the use of a broad spectrum of analytical in vitro methods. According to the study results, the antibacterial activity of EOs in their liquid forms varied from that of the volatile fractions. Overall, liquid and volatile forms of rosemary EO and tea tree EO displayed significant antibiofilm effectiveness. The outcomes indicate that these particular EOs possess the potential to be used in the therapy of P. aeruginosa infections.

Recent Advances in the Application of Essential Oils as Potential Therapeutic Candidates for Candida-Related Infections

Candidiasis (oral, vulvovaginal, or systemic bloodstream infections) are important human fungal infections associated with a high global prevalence in otherwise healthy adults but are also opportunistic infections in immunocompromised patients. With the recent discovery of the multidrug resistant—and often difficult to treat—Candida auris, as well as the rising costs associated with hospitalisations and the treatment of infections caused by Candida species, there is an urgent need to develop effective therapeutics against these pathogenic yeasts. Essential oils have been documented for many years as treatments for different ailments and are widely known and utilised in alternative and complementary therapies, including treating microbial infections. This review highlights knowledge from research on the effects of medicinal plants, and in particular, essential oils, as potential treatments against different Candida species. Studies have been evaluated that describe the experimental approaches used in investigating the anticandidal effects of essential oils (in vivo and in vitro), the established mode of action of the different compounds against different Candida species, the effect of a combination of essential oils with other compounds as potential therapies, and the evidence from clinical trial studies.

Screening of Antimicrobial Activity of Essential Oils against Bovine Respiratory Pathogens - Focusing on Pasteurella multocida

Administration of essential oils as natural plant products with antimicrobial activity might be an alternative to antibiotic treatment of bovine respiratory disease. The aim of this study was to analyse the in vitro antimicrobial activity of 11 essential oils against Pasteurella multocida isolated from the respiratory tract of calves using microdilution with determination of minimum inhibitory and bactericidal concentration as well as agar disc diffusion. Additionally, antimicrobial activity against Mannheimia haemolytica and bacteria in the Mannheimia clade was assessed by agar disc diffusion. Seven essential oil mixtures were also tested against all bacterial isolates. P. multocida was strongly inhibited by cinnamon cassia and lemongrass oil followed by coriander, winter savory, thyme, clove, and peppermint oil in the microdilution assays. Eucalyptus, wintergreen, spruce, and star anise oil showed lower activity. Comparison of both methods revealed an underestimation of cinnamon cassia oil activity by agar disc diffusion and conflicting results for wintergreen oil in microdilution, which precipitated in broth. Cinnamon cassia, thyme, wintergreen, lemongrass, and winter savory oil all showed strong antimicrobial activity against M. haemolytica. Bacteria in the Mannheimia clade were mostly inhibited by cinnamon cassia and thyme oil. Pasteurella isolates were more susceptible to inhibition by essential oils than Mannheimia isolates. Essential oil mixtures did not show stronger antibacterial activity than single essential oils. In conclusion, cinnamon cassia and lemongrass as well as coriander, winter savory, and thyme oil are promising candidates for treatment of P. multocida-associated bovine respiratory infections.

Antibacterial Activity of Thymus vulgaris L. Essential Oil Vapours and Their GC/MS Analysis Using Solid-Phase Microextraction and Syringe Headspace Sampling Techniques

While the inhalation of Thymus vulgaris L. essential oil (EO) is commonly approved for the treatment of mild respiratory infections, there is still a lack of data regarding the antimicrobial activity and chemical composition of its vapours. The antibacterial activity of the three T. vulgaris EOs against respiratory pathogens, including Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pyogenes, was assessed in both liquid and vapour phases using the broth microdilution volatilisation (BMV) method. With the aim of optimising a protocol for the characterisation of EO vapours, their chemical profiles were determined using two headspace sampling techniques coupled with GC/MS: solid-phase microextraction (HS-SPME) and syringe headspace sampling technique (HS-GTS). All EO sample vapours exhibited antibacterial activity with minimum inhibitory concentrations (MIC) ranging from 512 to 1024 μg/mL. According to the sampling technique used, results showed a different distribution of volatile compounds. Notably, thymol was found in lower amounts in the headspace—peak percentage areas below 5.27% (HS-SPME) and 0.60% (HS-GTS)—than in EOs (max. 48.65%), suggesting that its antimicrobial effect is higher in vapour. Furthermore, both headspace sampling techniques were proved to be complementary for the analysis of EO vapours, whereas HS-SPME yielded more accurate qualitative results and HS-GTS proved a better technique for quantitative analysis.

Bacterial Contamination Analysis of Residential Toilet Room Environment and Delivery of Residual Bacterial Growth Prevention Efficacy on Residential Toilet Permeable Surfaces Using Toilet Air Freshener Product

Toilet malodor is one of the most concerned malodor in residential houses, so that many technologies and products have been developed by which is aiming to remove or reduce such toilet malodor. Toilet malodour is generated from human faecal matters left inside of toilet bowl and from that deposited outside of toilet bowl such as toilet floors. In order to remove or prevent the malodor generated outside of toilet bowl, it is effective to do more frequent cleaning of toilet room surfaces or place a deodorizer which mask the malodour by perfume. We developed a toilet deodorizer which is preventing malodor generation outside of toilet bowl more effectively by delivering antibacterial efficacy on toilet room permeable surfaces. We analyzed microbiological quality of residential toilet rooms and found that toilet floor is the most contaminated location by bacteria, so that we developed a test method using materials frequently used for residential toilet floors such as vinyl cushion and using bacteria commonly found in toilet room environment. As the results, we found the product can provide bacterial growth prevention efficacy on permeable materials and prevent toilet malodor effectively.

Volatile Antimicrobial Agents and In Vitro Methods for Evaluating Their Activity in the Vapour Phase: A Review

This review summarizes data on the in vitro antimicrobial effectiveness of volatile agents of plant origin and in vitro methods for evaluating their activity in the vapour phase. As a result of literature analysis, the antimicrobial efficacy of vapours from 122 different plant species and 19 pure compounds examined in 61 studies using different in vitro tests against a broad spectrum of microorganisms was identified and summarized. In addition, 11 different techniques found in the literature are described in detail. An original classification of methods based on the solid and liquid matrix volatilization principle is proposed because carrier medium/matrix selection is crucial for the volatilization of any agents tested. This review should be useful for medicinal, pharmaceutical, food, and agricultural experts working in areas related to the management of infectious diseases (especially respiratory and skin infections), food preservation (active packaging), and protection of agriculture products (controlled atmosphere). It may also stimulate the interest of pharmaceutical, cosmetic, food, and agriculture industries in the research and development of new antimicrobial agents of natural origin. Since several original apparatuses previously developed for antimicrobial susceptibility testing in the vapour phase are described in this review, labware manufacturers may also be interested in this topic. The review also provides specific guidelines and recommendations for researchers studying the antimicrobial activity of volatile agents. The article will therefore appeal to communities of industrial stakeholders, pharmacists, physicians, food experts, agriculturists, and researchers in related areas such as pharmacology, medicinal chemistry, microbiology, natural product chemistry, food preservation and plant protection.

Chemical Composition and Determination of the Antibacterial Activity of Essential Oils in Liquid and Vapor Phases Extracted from Two Different Southeast Asian Herbs-Houttuynia cordata (Saururaceae) and Persicaria odorata (Polygonaceae)

Essential oils obtained via the hydrodistillation of two Asian herbs (Houttuynia cordata and Persicaria odorata) were analyzed by gas chromatography coupled to mass spectrometry (GC–MS) and gas chromatography with flame ionization detector (GC–FID). Additionally, both the liquid and vapor phase of essential oil were tested on antimicrobial activity using the broth microdilution volatilization method. Antimicrobial activity was tested on Gram-negative and Gram-positive bacteria—Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis, Streptococcus pyogenes, Klebsiella pneumoniae, Seratia marcescense and Bacillus subtilis. Hydrodistillation produced a yield of 0.34% (Houttuynia cordata) and 0.40% (Persicaria odorata). 41 compounds were identified in both essential oils. Essential oils contained monoterpenes and their oxidized forms, sesquiterpenes and their oxidized forms, oxidized diterpenes, derivates of phenylpropene and other groups, such as, for example, aldehydes, alcohols or fatty acids. Both essential oils were antimicrobial active in both vapor and liquid phases at least in case of one bacterium. They expressed various antimicrobial activity in the range of 128–1024 μg∙mL⁻¹, 512–1024 μg∙mL⁻¹ in broth and 1024 μg∙mL⁻¹, 512–1024 μg∙mL⁻¹ in agar, respectively. Research showed new interesting information about P. odorata and H. cordata essential oils and demonstrated that both essential oils could be possibly used in the field of natural medicine or natural food preservation.

New Tricks for Old Guys: Recent Developments in the Chemistry, Biochemistry, Applications and Exploitation of Selected Species from the Lamiaceae Family

Lamiaceae is one of the largest families of flowering plants comprising about 250 genera and over 7,000 species. Most of the plants of this family are aromatic and therefore important source of essential oils. Lamiaceae are widely used as culinary herbs and reported as medicinal plants in several folk traditions. In the Mediterranean area oregano, sage, rosemary, thyme and lavender stand out for geographical diffusion and variety of uses. The aim of this review is to provide recent data dealing with the phytochemical and pharmacological studies, and the more recent applications of the essential oils and the non-volatile phytocomplexes. This literature survey suggests how the deeper understanding of biomolecular processes in the health and food sectors as per as pest control bioremediation of cultural heritage, or interaction with human microbiome, fields, leads to the rediscovery and new potential applications of well-known plants.

Essential oils inhibit the bovine respiratory pathogens Mannheimia haemolytica, Pasteurella multocida and Histophilus somni and have limited effects on commensal bacteria and turbinate cells in vitro

AIMS

The objective of this study was to determine antimicrobial activities of essential oils (EOs) against bovine respiratory disease (BRD) pathogens and nasopharyngeal commensal bacteria, as well as cytotoxicity in bovine turbinate (BT) cells in vitro.

METHODS AND RESULTS

The chemical composition of 16 EOs was determined using gas chromatography-mass spectrometry. All EOs were first evaluated for growth inhibition of a single BRD pathogen Mannheimia haemolytica serotype 1 strain (L024A). The most inhibitory EOs (n = 6) were then tested for antimicrobial activity against multidrug-resistant strains of M. haemolytica (serotypes 1, 2 and 6); the BRD pathogens Pasteurella multocida and Histophilus somni, as well as commensal bacteria that were isolated from the nasopharynx of feedlot cattle. The cytotoxicity of 10 EOs was also evaluated using a BT cell line. The EOs ajowan, thyme and fennel most effectively inhibited all BRD pathogens tested including multidrug-resistant strains with minimum inhibitory concentrations (MIC) of ≤0·025% (volume/volume, v/v). For these EOs, the MIC was 2-32 fold greater against commensal bacteria, compared to BRD-associated pathogens. No cytotoxic effects of EOs against BT cells were observed within the tested range of concentrations (0·0125-0·4%, v/v).

CONCLUSIONS

The EOs ajowan, thyme and fennel inhibited M. haemolytica, P. multocida and H. somni at a concentration of 0·025% and had minimal antimicrobial activity against nasopharyngeal commensal bacteria and cytotoxicity against BT cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated that EOs may have potential for intra-nasal administration to mitigate bovine respiratory pathogens in feedlot cattle.

Essential oils in vapor phase as alternative antimicrobials: A review

The antimicrobial effectiveness of essential oils (EOs) against many foodborne microorganisms when applied by direct contact has been extensively demonstrated. However, the vapor phase and volatile components present in EOs have not been thoroughly investigated; there are a small number of published reports on the antimicrobial activity of some EOs and a few of their components against selected microorganisms. It is well known that the antimicrobial activity of EOs depends mainly on their chemical composition. It is also important; however, to understand the volatility of these compounds as well as the methodologies used to evaluate the antimicrobial effectiveness of their vapor phase. This review focuses on recent research regarding the chemical composition of EOs, their biological activity and mechanisms of action, the antimicrobial activity of EOs in the vapor phase, the different techniques that have been proposed to evaluate the antimicrobial effects of EOs in the vapor phase, and actual and potential applications of EOs in the vapor phase. Although there is still no standard methodology for determining the activity of EOs in the vapor phase, results reported thus far are encouraging and suggest possible applications in food preservation.