Inhibition Zone Diameter Values Research Articles

Phytochemical Screening and Antibacterial Activity of Commercially Available Essential Oils Combinations with Conventional Antibiotics against Gram-Positive and Gram-Negative Bacteria.

The present study aims to evaluate the antibacterial activity of five commercially available essential oils (EOs), Lavender (LEO), Clove (CEO), Oregano (OEO), Eucalyptus (EEO), and Peppermint (PEO), against the most-known MDR Gram-positive and Gram-negative bacteria-Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), and Pseudomonas aeruginosa (ATCC 27853)-alone and in various combinations. Gas Chromatography-Mass Spectrometry (GC-MS) analysis established their complex compositions. Then, their antibacterial activity-expressed as the inhibition zone diameter (IZD) value (mm)-was investigated in vitro by the diffusimetric antibiogram method, using sterile cellulose discs with Ø 6 mm impregnated with 10 µL of sample and sterile borosilicate glass cylinders loaded with 100 µL; the minimum inhibitory concentration (MIC) value (µg/mL) for each EO was calculated from the IZD values (mm) measured after 24 h. The following EO combinations were evaluated: OEO+CEO, CEO+EEO, CEO+PEO, LEO+EEO, and EEO+PEO. Then, the influence of each dual combination on the activity of three conventional antibacterial drugs-Neomycin (NEO), Tetracycline (TET), and Bacitracin (BAC)-was investigated. The most active EOs against S. aureus and E. coli were LEO and OEO (IZD = 40 mm). They were followed by CEO and EEO (IZD = 20-27 mm); PEO exhibited the lowest antibacterial activity (IZD = 15-20 mm). EEO alone showed the highest inhibitory activity on P. aeruginosa (IZD = 25-35 mm). It was followed by CEO, LEO, and EEO (IZD = 7-11 mm), while PEO proved no antibacterial action against it (IZD = 0 mm). Only one synergic action was recorded (OEO+CEO against P. aeruginosa); EEO+PEO revealed partial synergism against S. aureus and CEO+PEO showed additive behavior against E. coli. Two triple associations with TET showed partial synergism against E. coli, and the other two (with NEO and TET) evidenced the same behavior against S. aureus; all contained EEO+PEO or CEO+PEO. Most combinations reported indifference. However, numerous cases involved antagonism between the constituents included in the double and triple combinations, and the EOs with the strongest antibacterial activities belonged to the highest antagonistic combinations. A consistent statistical analysis supported our results, showing that the EOs with moderate antibacterial activities could generate combinations with higher inhibitory effects based on synergistic or additive interactions.

Effect of Co-Surfactants on Properties and Bactericidal Activity of Cu2O and Hybrid Cu2O/Ag Particles.

Nanomaterials based on metal oxides, especially Cu2O, have received much attention in recent years due to the many unique properties of the surface plasmon resonance they provide. The report presented the co-precipitation method, a simple preparation method to produce Cu2O oxide particles. In addition, to improve the unique antibacterial properties of Cu2O, a proposed method is to attach Ag nanoparticles to the surface of Cu2O particles. The Cu2O and Cu2O-Ag particles were synthesized based on redox reactions using ascorbic acid (LAA) as a reducing agent. Moreover, in this experiment, two surfactants, polyethylene glycol 6000 (PEG 6000) and sodium dodecyl sulfate (SDS), were added during the manufacturing process to create particle samples and particle combinations with better properties than the original sample. Changes in the characteristics and properties of particle samples are determined by many different physical and chemical methods such as ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), noise X-ray radiation (XRD), scanning electron microscope (SEM), dynamic light scattering (DLS), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). Finally, the activity against bacteria, including E. coli and S. aureus, was also tested using the agar well diffusion method to determine the zone of inhibition. The results improved the particle size value, which decreased by half to 200 nm when two additional surfactants, PEG and SDS, were added. In addition, the antibacterial ability has also been shown to increase significantly when the diameter of the bacterial inhibition zone increased significantly, reaching values of 20 mm (Cu2O/Ag/SDS) and 32 mm (Cu2O/Ag/PEG) for the E. coli bacterial strain. The initial test sample was only about 14 mm in size. The S. aureus bacterial strain also had a similar improvement trend after adding Ag to the Cu2O surface with the appearance of two surfactants, SDS and PEG. The inhibition zone diameter values reached the optimal value at 36 mm in the Cu2O/Ag/PEG particle combination sample compared to only the initial 26 mm in the Cu2O particle sample. Finally, the particle samples are added to the acrylic emulsion paint film to evaluate the changes. Positive results were obtained, such as improvement in adhesion (1.22 MPa), relative hardness (240/425), and sand drop resistance (100 L/mil) in the Cu2O/Ag/PEG particle combination sample, which showed the correctness and accuracy of the research.

Prominent bactericidal characteristics of silver-copper nanocomposites produced via pulse laser ablation

This paper reports the characterization and antibacterial performance evaluation of some spherical and stable crystalline silver (Ag)/copper (Cu) nanocomposites (Ag-CuNCs) prepared in deionized water (DIW) using pulse laser ablation in liquid (PLAL) method. The influence of various laser fluences (LFs) on the structural, morphological, optical and antibacterial properties of these NCs were determined. The UV–Vis absorbance of these NCs at 403 nm and 595 nm was gradually increased accompanied by a blue shift. XRD patterns disclosed the nucleation of highly crystalline Ag-CuNCs with their face centered cubic lattice structure. TEM images showed the existence of spherical NCs with size range of 3–20 nm and lattice fringe spacing of approximately 0.145 nm. EDX profiles of Ag-CuNCs indicated their high purity. The antibacterial effectiveness of the Ag-CuNCs was evaluated by the inhibition zone diameter (IZD) and optical density (OD600) tests against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The proposed NCs revealed the IZD values in the range of 22–26 mm and 20–25 mm when tested against E. coli and S. aureus bacteria, respectively. The Ag-CuNCs prepared at LF of 14.15 J/cm2 revealed the best bactericidal activity. It is established that by controlling the laser fluence the bactericidal effectiveness of the Ag-CuNCs can be tuned.

Optimization of Subcritical Fluid Extraction for Total Saponins from Hedera nepalensis Leaves Using Response Surface Methodology and Evaluation of Its Potential Antimicrobial Activity

(1) Background: Hedera nepalensis (Araliaceae) is a recognized medicinal plant founded in Asia that has been reported to work in antioxidant, antifungal, antimicrobial, and antitumor capacities. (2) Methods: The subcritical fluid extraction of saponin from Hedera nepalensis leaves and the optimum of the extraction process based on yield of saponin contents (by calculating the hederacoside C contents in dried Hedera nepalensis leaves) are examined by response surface methodology (RSM). Furthermore, the antimicrobial activity of the extract is tested for potential drug applications in the future. (3) Results: Based upon RSM data, the following parameters are optimal: extraction time of 3 min, extraction temperature of 150 °C, and a sample/solvent ratio of 1:55 g/mL. Under such circumstances, the achieved yield of saponin is 1.879%. Moreover, the extracts inhibit the growth of some bacterial strains (Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenza) at a moderate to strong level with inhibition zone diameter values ranging from 12.63 to 19.50 mm. (4) Conclusions: The development of such a model provides a robust experimental process for optimizing the extraction factors of saponin contents from Hedera nepalensis extract using subcritical fluid extraction and RSM. Moreover, the current work reveals that saponin extracts of Hedera nepalensis leaves exhibit a potential antimicrobial activity, which can be used as scientific evidence for further study.

The effect of thymus syriacus plant extract on the main physical and antibacterial activities of ZnO nanoparticles synthesized by SILAR method

This study aimed to determine the main physical properties of green synthesized ZnO nanoparticles (ZnO-NPs) using Thymus syriacus plant extract and their antibacterial activities against eight different Gram-positive and Gram-negative plant bacterial disease agents. The surface morphological, structural, optical and electrical attributes of the ZnO films were analyzed by various types of characterization techniques. The authors have observed that the microstructural and surface morphological properties considerably changed by using T. syriacus plant extract. UV–Vis. analysis showed that the bandgap values are increased from 3.17 to 3.28 eV with the T. syriacus content in the growth solution. Impedance measurements presented an increase of the semicircle diameters with the increase % of T. syriacus. The antibacterial effectiveness of ZnO-NPs was evaluated against plant pathogenic bacterial species by using the agar disc diffusion method. Established on inhibition zone diameter values, ZnO-NPs displayed varying levels of antibacterial activities against all bacterial species tested. Gram-positive bacterial species were found more sensitive than Gram-negative species. In comparison, the highest antibacterial activity was displayed against Clavibacter michiganensis subsp. michiganensis and Bacillus subtilis subsp. subtilis, the lowest antibacterial activity was recorded for Pseudomonas corrugata. The present research findings suggest that the green synthesized ZnO-NPs have a prospective to be used as optoelectronic materials and antibacterial agents against plant pathogenic bacterial disease.

SKRINING FITOKIMIA DAN UJI AKTIVITAS ANTIBAKTERI EKSTRAK ETANOL DAUN RACUN AYAM (Brucea javanica [L.] Merr.) ASAL KALIMANTAN SELATAN

Racun ayam is one of the plants which has several activities in its fruits, one of which is an antibacterial. This study aims to determine the antibacterial activity of ethanol extract of racun ayam leaves. The extraction was done by maceration method using ethanol as a solvent. Antibacterial activity assay was carried out on S. aureus, E. coli, and P. aeruginosa bacteria by disk diffusion method at the concentrations of 80, 100, and 120 ppm. The results showed that the ethanol extract of B. javanica leaves had the greatest inhibition zone on E. coli with inhibition zone diameter values ​​at 80, 100, and 120 ppm were 11.7 mm, 14.5 mm and 19.67 mm respectively. Inhibition zones in S. aureus could only be seen at 100 and 120 ppm which had inhibition zone diameters at 1.17 mm and 2.17 mm respectively, whereas in P. aeruginosa they did not have any inhibitory zone values. The results of statistical analysis showed a significance of the inhibition zone diameter values ​​of E. coli bacteria starting at 80 ppm with a sig value of 0.034. Due to a sig value was <0.05, it was categorized as significantly different from the negative control. The bacteria of S. aureus which had ​​<0.05 for sig values only found on 100 ppm and 120 ppm. Bacteria P. aeruginosa which had sig value >0.05 was not significantly different at all concentrations

Tıbbi Bitkilerden Elde Edilen Uçucu Yağların Kimyasal Bileşimi ve Gal Oluşturan Bitki Patojeni Bakteriyel Hastalık Etmenlerine Karşı Antibakteriyel Etkinlikleri

The aims of this study were to determine chemical composition of essential oils from different plant species and their antibacterial activities against gal-forming plant pathogenic bacterial disease agents Rhizobium radiobacter, Pseudomonas savastanoi pv. savastanoi and P.savastanoi pv. nerii. The chemical compositions of essential oils were identified by GC/MS. The major constituents of the essential oils were carvacrol in Thymbra spicata var. spicata (66.88%) and Origanum syriacum (79.8%), thymol in Thymus serpyllum (41.03%), geranial in Thymus sipyleus (13.72%) and Melissa officinalis (30.4), 4-terpineol in Origanum majorana (31.67%), linalool in Ocimum basilicum (30.23%), carvone in Mentha spicata (55.58%), 1,8 cineole in Lavandula stoechas var. stoechas (35.5%), Laurus nobilis (35.5%) and Rosmarinus officinalis (18.47%), camphor in Salvia officinalis (24.59%) and trans-anethole in Foeniculum vulgare (82.8%) essential oils, respectively. Based on inhibition zone diameter values, essential oils showed very strong antibacterial activities against P.savastanoi pv. savastanoi (7.0-44.67 mm), followed by R.radiobacter (9.6-37.67 mm) and P.savastanoi pv. nerii (6.33-18.33 mm). Essential oils of plants belong to Lamiaceae family were generally found to be more efficient than those belong to Lauraceae and Apiaceae families. The essential oils of O.syriacum, T.serpyllum and T.spicata var. spicata were found to be the most promising essential oils displaying the highest antibacterial activities against all tested bacterial species. The findings of the present study revealed that essential oils have a potential to be used as antibacterial agents against gall forming bacterial disease agents.

Chemical Composition and Antibacterial Activity of Lippia multiflora Moldenke Essential Oil from Different Regions of Angola

The purpose of the study was to determine the chemical composition and antibacterial activity of Lippia multiflora Moldenke essential oils (EOs) collected in different regions of Angola. Antibacterial activity was evaluated using the agar wells technique and vapour phase test. Analysis of the oils by GC/MS identified thirty-five components representing 67.5 to 100% of the total oils. Monoterpene hydrocarbons were the most prevalent compounds, followed by oxygenated monoterpenes. The content of the compounds varied according to the samples. The main components were Limonene, Piperitenone, Neral, Citral, Elemol, p-cymene, Transtagetone, and Artemisia ketone. Only one of the eleven samples contained Verbenone as the majority compound. In the vapour phase test, a single oil was the most effective against all the pathogens studied. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) of components of the selected EOs and inhibition zone diameter values of agar wells technique allowed us to identify a variability between the plants from the two provinces, but also intraspecific variability between sub-groups within a population. Each group of essential oils constituted a chemotype responsible for their bacterial inhibition capacity. The results presented here suggest that Angolan Lippia multiflora Moldenke has antibacterial properties and could be a potential source of antimicrobial agents for the pharmaceutical and food industry.

Cu- Zeolitic Imidazolate Framework-8 Loaded on Magnetic Nanofiber as a High-efficient Antimicrobial Scaffold

In this work, CoFe2O4 was synthesized as magnetic agent and blended with chitosan-poly vinyl alcohol (CS-PVA) to fabricate magnetic nanofiber (MNF) by electrospinning method. Zeolitic imidazolate framework-8 (ZIF-8) crystals were used as a porous media to prepare MNF@ZIF-8 nanocomposite. Two different methods were employed for doping copper ions into the MNF@ZIF-8 structure by adsorption and encapsulation procedures. Characterization clarification of as synthesis materials were performed. Mechanical tests showed that magnetic nanoparticles caused to improve tension resistance of CS-PVA nanofibrous scaffold. Antimicrobial tests for the prepared materials were done in against two types of Gram-positive and Gram-negative strains. The inhibition zone diameter values for Cu2+ adsorbed-MNF@ZIF-8 (33 mm and 24 mm for E.coli and S.aureus, respectively) were better than that of Cu2+ encapsulated-MNF@ZIF-8 (32 mm and 18 mm for E.coli and S.aureus, respectively). The obtained results showed that the prepared copper doped MNF@ZIF-8 can be potentially used as a scaffold for further investigations in practical wound healing applications.

Investigation of the antimicrobial effects of Sapindus mukorossi on endodontic pathogens

Endodontic infections have a polymicrobial nature. Thus, eliminating the microorganisms from infected root canals without damaging healthy surrounding tissue is a major concern. Sapindus mukorossi (S. mukorossi) is a natural product with potential antimicrobial effects. The aim of this study was to evaluate whether various extract solutions of S. mukorossi have an antimicrobial activity against specific endodontic pathogens. Extracts were obtained from S. mukorossi fruit pericarps using methanol, ethanol, butanol and distilled water solvents. The inhibition zone, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) were determined with disc diffusion assay, broth microdilution assay and agar dilution assay. Antimicrobial inhibitory activity was observed with all four different solvent extracts of S. mukorossi against Fusobacterium nucleatum American Type Culture Collection (ATCC) 25586, Porphyromonas gingivalis ATCC 33277 and Actinomyces odontolyticus (clinical isolate). The MIC values were ranged 10.24-10.24, 0.01-0.64 and 1.28- 2.56 mg/mL, respectively. The MBC value was not detected for Fusobacterium nucleatum ATCC 25586. The MBC values were 0.02-1.25 and 2.56-5.12 mg/ mL for Porphyromonas gingivalis ATCC 33277 and Actinomyces odontolyticus (clinical isolate), respectively. Antifungal activities were also observed with the four different solvent extracts of S. mukorossi against Candida albicans ATCC 10231 and C. albicans clinical isolates 1, 2 and 3. The inhibition zone diameter values were in the range of 18-21 mm. The MIC values for C. albicans ATCC 10231 and C. albicans clinical isolates 1, 2 and 3 were 0.2-0.4 and MFC values were 0.4-0.8 mg/mL, respectively. The antimicrobial effects of the S. mukorossi fruit pericarp extract inhibited the growth of P. gingivalis, A. odontolyticus, F. nucleatum, and especially the C. albicans strains. S. mukorossi extract has interesting potential as an antimicrobial agent against endodontic pathogens.

Correlation between chemical composition and antibacterial activity of some Lamiaceae species essential oils from Tunisia

BackgroundLamiaceae family is one of the most diverse and common plant families in terms of ethnomedicine due to their potential therapeutic effects. The aim of this study is to investigate the correlation between the chemical composition and the antibacterial effect of five essential oils from this family against five reference bacterial strains responsible of nosocomial diseases and foodborne illnesses.MethodsThe commercial essential oils of Tunisian Rosmarinus officinalis, Thymus capitatus, Origanum majorana and Salvia officinalis were analyzed by GC/FID and GC-MS. Essential oils were evaluated for their antibacterial activities by disc diffusion and microbroth dilution methods against five reference bacterial strains: Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica, Bacillus subtilis and Staphylococcus aureus. The inhibition zone diameter values and the twenty major compounds of the selected essential oils were subjected to PCA and HCA analysis.ResultsAnalysis by GC/FID and GC/MS allowed the identification of ninety-one components representing 96.0 to 98.2% of the total oils. The different component contents varied according to the species. The main components were carvacrol, 1,8-cineole, α-thujone, α-terpineol and α-pinene. The PCA and the HCA of the selected essential oil components and the inhibition zone diameter (IZD) values identified four species groups and subgroups. Each essential oils group constituted a chemotype responsible for their bacterial inhibition ability. Thymus capitatus essential oil showed the strongest antibacterial activity with MBC ranging from 0.73 to 2.94 mg mL− 1.ConclusionRosmarinus officinalis, Thymus capitatus, Origanum majorana and Salvia officinalis essential oils have shown promising antibacterial activities against reference bacterial strains responsible for nosocomial diseases and foodborne illnesses.

Experimental and In-Silico Investigation of Anti-Microbial Activity of 1-Chloro-2-Isocyanatoethane Derivatives of Thiomorpholine, Piperazine and Morpholine.

The Antibiogram properties of 1-chloro-2-isocyanatoethane derivatives of thiomorpholine (CTC), piperazine (CPC) and morpholine (CMC) were evaluated by the approved agar well diffusion, the minimum inhibitory concentration (MIC) and in silico techniques. A total of fourteen microbial cultures consisting of ten bacteria and four yeast strains were used in the biological study while affinity of the compounds for DNA gyrase, a validated antibacterial drug target, was investigated by docking method. Results indicate that both thiomorpholine and piperazine had zero activity against the Gram negative organisms tested. With morpholine, similar result was obtained except that cultures of Escherichia coli (ATCC 15442) and Salmonella typhi (ATCC 6539) presented with weak sensitivity (7–8 mm) as shown by the inhibition zone diameter (IZD) measurement. The Gram positive organisms were more sensitive to morpholine than the other compounds. The highest IZD values of 15–18 mm were achieved except for Streptococcus pneumoniae (ATCC 49619) in which mobility of the compound stopped after 12 mm. S. pneumoniae was resistant to both thiomorpholine and piperazine. The yeast strains were not sensitive to any of the studied compounds investigated. The MIC tests evaluated against a reference antibiotic show that while morpholine was most active at 4 μg.ml-1 against both B. cereus ATCC (14579) and B. subtilis, the least active compound was thiomorpholine which inhibited S. aureus (ATCC 25923) at 64 μg.ml-1. The three compounds demonstrated high affinity for the target protein (DNA gyrase) ranging from -4.63 to -5.64 Kcal/mol and even showed better ligand efficiencies than three known antibiotics; chlorobiocin, ciprofloxacin and tetracycline. This study identified the studied compounds as potential antibiotic leads with acceptable physicochemical properties and gave the molecular basis for the observed interactions between the compounds and the target protein which can be harnessed in structural optimization process.

In Vitro Antimicrobial Effect of Egyptian Propolis Pastes on Microorganisms in Necrotic Primary Molars : A Comparative Study

Background: Primary teeth are very important to be restored in children, so using natural antimicrobial products is nessecary to protect children from complications of chemical drugs. Objectives: The aim of this study was to evaluate the antimicrobial effect of three intracanal propolis containg pastes against polymicrobial cultures collected from thirty five primary molars of 4-8-years old children of both sexes having necrotic root canals. Methodology: Sterile paper point were introduced in the root canal of the necrotic teeth, placed in a transport medium containing brain heart infusion (BHI), followed by identification of the isolated organisms. Agar-well diffusion technique was used to determine the antimicrobial activity of the following pastes; Metapex mixed with propolis (paste 1), zinc oxide eugenol mixed with propolis (paste 2) and ethanol extract of propolis (EEP) paste (paste 3). Results: The predominant organisms isolated were Streptococcus mutans (51.4%), Enterococcus species (34.2%), followed by Porphyromonas gingivalis (28.5%), Fusobacterium nucleatum (25.6%) and Prevotella nigrescens (8.5%). There was a statistically significant difference between inhibition zone diameters of the different paste types (P-value <0.001). Pair-wise comparison between the paste types revealed that paste 2 showed statistically significantly highest mean inhibition zone diameter values. There was no statistically significant difference between paste 1and paste 3; both showed a statistically significant lowest mean inhibition zone diameter values. Conclusion : The addition of propolis to Metapex and zinc oxide eugenol could potentiate the antimicrobial effect of each other.

Antimicrobial susceptibility and plasmid profiles of Flavobacterium psychrophilum strains isolated in Chile

Flavobacterium psychrophilum is one of the most threatening bacterial infections for freshwater fish species in the world and is of considerable economic significance to aquaculture producers. Up to now, antimicrobial therapies represent the only recourse to control the disease in farmed fish. In this study, a total of 40 F. psychrophilum isolates obtained from Chilean salmonid farms were tested to determine their antimicrobial susceptibility using minimum inhibitory concentration (MIC) determinations and disk diffusion tests, for oxytetracycline (OTC), florfenicol (FLO) and oxolinic acid (OXA) and also to examine the plasmid profile to assist in the characterization of the strains isolated from different salmonid species. In addition, the presence of mutations in the quinolone resistance‐determining region (QRDR) was evaluated. Normalized resistance interpretation (NRI) of MIC data suggested cut-off values for non-susceptible at R>0.203, and 2.35μgmL−1 for OTC, and FLO, respectively. For OXA a slightly larger coefficient of variation in the calculations required a conservative estimate at R≥16μgmL−1. Of the 40 Chilean isolates studied, 90%, 92.5%, and 85% F. psychrophilum were resistant to the three antimicrobials. In the disk diffusion tests, all isolates produced zones of inhibition to OTC30 and FLO30. However, there was a low or no correlation between MIC results and inhibition zone diameter values and valid NRI calculations were not possible to perform. For OXA2 disks, no zones were observed (<7mm). No correlation was found between quinolone resistance and PCR-RFLP analysis; whereas 5 isolates had mutations in the QRDR of gyrA. Thirty-nine of 40 isolates possessed a single plasmid (15 isolates with 3.5kb) or combinations of two plasmids (17 and 7 isolates of sizes 1.5 and 3.5kb and 2.7 and 3.5kb, respectively), but a relationship between plasmid and resistance could not be established. In summary, we demonstrate in this work by MIC assays that high levels of resistance to OTC, FLO and OXA exist among Chilean isolates, which could be associated with the high amounts of antimicrobials applied at the Chilean farms to control outbreaks caused by F. psychrophilum. Disk contents for disk diffusion tests were not suitable for this bacterium. Surveillance in the use of drugs is recommended in cultured freshwater fish to prevent resistance problem.

Chemical composition and antimicrobial activities of essential oil of Blumea megacephala.

Blumea megacephala essential oil, obtained through steam distillation of samples collected from the Shiwang Mountains in Guangxi Province, China, was analyzed using GC-FID and GC-MS. Among the 65 compounds identified in the oil, the main compounds were borneol (13.6 %), β-caryophyllene (9.56 %), germacrene D (9.09 %), sabinene (6.37 %), and α-humulene (4.78 %). Antimicrobial activity revealed that the essential oil (1000 μg/disc) has promising antimicrobial effects against several pathogens, giving satisfactory inhibition zone diameter values (21.5, 21.6, 23.4, 23.8, 21.9) and MIC values (125, 125, 62.5, 125, 125 µg/ml) against Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli), Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus), and yeast (Hansenula anomala). Antioxidant and antimicrobial activities were correlated with chemical composition.

Comparison of 30 μg and 120 μg gentamicin disks for the prediction of gentamicin resistance in Enterococcus faecalis

Single strain regression analysis was performed on PDM II medium for E. faecalis with 10, 30 and 120 micrograms gentamicin disks using E. faecalis, strain ATCC 29212 as the reference. This method permits the calculation of zone diameters corresponding to different MIC values for different disk contents. The lack of discrimination between normal low-level resistant strains and high-level resistance using the 10 micrograms disk was confirmed. However, both the 30 micrograms and 120 micrograms disks seemed to provide a separation of the normal low-level gentamicin-resistant population from strains with increased resistance. Since the 30 micrograms disk is used routinely in some countries, there should be no need for an extra high content disk in these laboratories. This was confirmed when 96 clinical isolates of E. faecalis were analysed and the results of routine disk diffusion tests were compared with the MIC values. Two of the strains showed high-level gentamicin resistance (greater than 2000 mg/l) and produced no zone of inhibition. The other 94 isolates showed gentamicin MIC values between 4-16 mg/l, and 72 of the MIC results were 8 mg/l. The zone diameters for these strains ranged between 15 and 25 mm with a mean of 18.2 and a median value of 18 mm. In order to include statistical considerations of the zone size populations for setting of breakpoints, a study of gentamicin zone size distributions was performed for several bacterial species. Inhibition zone diameter values around the 30 micrograms gentamicin disk for 2079 clinical isolates of E. faecalis, 2268 S. aureus, 3201 E. coli and 547 strains of P. mirabilis from different years were plotted as histograms. Tests for agreement with a Gaussian distribution showed that the histograms were slightly peaked and skewed towards higher zone values. Parametric and non-parametric statistical tests were compared and the results showed that means and medians were very similar and that parametric fractile estimations at the lower end of the histogram populations were conservative and could be used in view of a slightly lower rate of false resistance. The 1% parametric fractile of 12 mm was selected as a suitable breakpoint for the identification of normal, low-level resistant isolates of E. faecalis using the standardized disk test of the Swedish Reference Group for Antibiotics.