Mean Minimum Inhibitory Concentration Values Research Articles

Minimum Inhibitory Concentration of Glyphosate and of a Glyphosate-Containing Herbicide Formulation for Escherichia coli Isolates - Differences Between Pathogenicand Non-pathogenic Isolates and Between Host Species.

Glyphosate is the most extensively used herbicide in the world. However, concerns regarding its safety, side effects, and impact on other organisms have increased in recent years. This is the first study to analyze a large set of recent and historical Escherichia coli isolates varying in pathogenicity and beta-lactam resistance from different host species for their susceptibility to glyphosate isopropylamine salt (IPA), the active ingredient of the herbicide, and to a complete glyphosate-containing formulation (Roundup LB Plus). For this, minimum inhibitory concentrations (MIC) were determined for 238 E. coli isolates by broth microdilution in Mueller Hinton I media followed by the statistical analyses using Mann-Whitney-U test, multivariable analysis of variance (ANOVA) and a multivariable proportional-odds ordinal regression model. While the overall MIC distribution was narrow and lacked a highly resistant sub-population for both substances, statistical analyses revealed small but significant associations between glyphosate resistance levels and different factors tested. Mean MIC values for the entire dataset showed a higher level of resistance to the complete glyphosate-containing formulation (40 mg/ml IPA) than to pure glyphosate (10 mg/ml IPA) in E. coli. Isolates that originated from poultry had significantly higher MIC values for both pure glyphosate and the complete formulation. Pathogenic and non-extended-spectrum beta-lactamase (non-ESBL) E. coli isolates each showed significantly higher MIC values compared to commensals and ESBL-producing E. coli in pure glyphosate, but not in the complete formulation. Recently sampled isolates showed statistically higher MICs than the isolates of the historic standard E. coli collection of reference in pure glyphosate, when tested by nonparametric Mann-Whitney-U test, but not in the multivariable model. Further investigations are necessary to confirm whether these associations have a casual relationship with the glyphosate use or are the consequence of co-selection due to the increased application rates of antibiotics, heavy metals or other biocides. A possible accumulation of pathogenic bacteria in livestock animals fed with glyphosate-containing feed should also be considered.

Molecular types of Cryptococcus neoformans and Cryptococcus gattii in Western Australia and correlation with antifungal susceptibility

Cryptococcus neoformans and Cryptococcus gattii species complexes have a worldwide distribution; however, there is geographical variation in the prevalence of different molecular types. Additionally, antifungal susceptibility differences between molecular types have been demonstrated. This study investigates the distribution of cryptococcal molecular types among human clinical isolates over a 10-year period from a Western Australian population. Molecular type was determined based on polymorphisms in the phospholipase gene locus identified through amplification and sequencing. Minimum inhibitory concentrations (MICs) were identified for fluconazole, 5-fluorocytosine, posaconazole, itraconazole, voriconazole, and amphotericin B. Most isolates were C. neoformans complex (42) of which over half were molecular type VNI (22) followed by VNII (20). Among the remaining C. gattii complex (13) the majority were VGI (11) with VGII (2) uncommonly found. All isolates demonstrated low MICs to antifungal agents including fluconazole. Geometric mean MIC values against 5-fluorocytosine for VNI (1.741mg/l) were significantly higher than those for VGI (0.47mg/l, P = .002). Similarly fluconazole geometric mean MICs against fluconazole for VNI (2.3mg/l) were significantly higher than VNII (0.87mg/l, P = .036). These data reveal the presence of four molecular types (VNI, VNII, VGI and VGII) within clinical Western Australian cryptococcal isolates and, while elevated antifungal MICs were not encountered, significant molecular type dependent differences in susceptibility were found.

Impact of heavy metals on inhibitory concentration of Escherichia coli-a case study of river Yamuna system, Delhi, India.

The occurrence of resistant bacteria to specific heavy metals can be associated with increasing load of the metals in the environment. River Yamuna is polluted by various toxic heavy metals discharged by several industrial and agricultural sources. Therefore, the use of heavy metal-resistant bacteria as an indicator of metal pollution was tested in the present study. For the purpose of the study, the heavy metal resistance status of 42 Escherichia coli strains isolated from River Yamuna water from 7 sampling sites within a span of 2years was determined using growth curves and plate dilution method in terms of minimum inhibitory concentration (MIC) values by comparing with MIC value of control strain. Seasonally, the lowest mean MIC value was observed for bacterial strains isolated in post-monsoon (December) 2013 and highest mean MIC value was observed for bacterial strains isolated in monsoon (August) 2015. Site-wise analysis of the maximum mean MIC values for all the isolated strains showed the highest mean Ni MIC value for the bacterial strains isolated from site S4 (ITO), highest mean Cu MIC, Cr MIC, and Fe MIC values for the bacterial strains isolated from site S2 (Najafgarh drain intermixing zone) and highest mean Cd MIC, Pb MIC, and Zn MIC values for the bacterial strains isolated from site S7 (Shahdara drain intermixing zone). Correlation analysis between mean MIC site-wise results with mean heavy metal site-wise concentrations showed significant positive correlation indicating that the higher the mean concentration of a given heavy metal at a given site, the higher the mean MIC value for the strains isolated from the same site indicating higher level of resistance. Overall, the present study has shown that the presence of heavy metals in River Yamuna caused due to indiscriminate discharge of various effluents from different kind of sources as well as due to insufficient treatment capacity of sewage treatment plants as well as common effluent treatment plants, has serious impacts on its bacterial microflora as it leads to the development of resistant strains.

Antibacterial Activity of Pomegranate (Punica granatum L.) Seed and Peel Alcoholic Extracts on Staphylococcus aureus and Pseudomonas aeruginosa Isolated From Health Centers

Introduction: Pomegranate (Punica granatum L.) is an ancient fruit with numerous phytochemical bioactive compounds. In this study, the antibacterial activity of ethanolic extracts of pomegranate peels and seeds were investigated against Pseudomonas aeruginosa and Staphylococcus aureus clinical isolates from Tabriz health centers (2017). Materials and Methods: The ethanolic extracts of pomegranate seed and peel were prepared and GC-MS chromatogram analyzed using Agilent 7890B gas chromatography. The antibacterial activities of extracts were evaluated by agar diffusion and microbroth dilution methods against clinical isolates of P. aeruginosa (n = 10), S. aureus (n = 10) and standard strains. Results: The ethanolic extracts of pomegranate seed and peel showed inhibitory effects on clinical isolates of P. aeruginosa and S. aureus. The minimum inhibitory concentrations (MICs) of pomegranate peel and seed extracts were 12.5 and 25.0 mg/mL, respectively. In addition, the minimum bactericidal concentrations (MBCs) of pomegranate peel and seed extracts were found to be 25.0 and 50 mg/mL, respectively. In all of the studied bacterial isolates, the MICs and MBCs values for pomegranate seed extract were significantly higher than those for pomegranate peel extract (P < 0.05). The mean inhibition zones and MICs values indicated that the antibacterial activity of pomegranate peel extract had more potent effect on studied bacterial isolates compared with pomegranate seed extract. Conclusions: According to the findings, the pomegranate peel and seed extracts showed antibacterial activities against bacterial isolates in this study; however, the peel extract had a stronger antibacterial effect than the seed extract. Therefore, further studies including cell toxicity assay and in vivo investigations are recommended. © 2018 The Author(s).

Reduced Antifungal Susceptibility of Vulvovaginal Candida Species at Normal Vaginal pH Levels: Clinical Implications.

The aims of the study were to assess for differences in antifungal in vitro potency at pH 7 and pH 4 and to discuss any potential clinical implications of that difference. A retrospective analysis of 217 first positive yeast cultures from 217 patients. Yeast isolates underwent antifungal susceptibility testing, with minimum inhibitory concentrations (MICs) (microgram per milliliter) measured at pH 7 and pH 4 for fluconazole, itraconazole, miconazole, clotrimazole, terconazole, and nystatin. Only the first isolates collected from each patient were included in the analysis. Yeast first isolates included 173 Candida albicans, 15 Candida glabrata, and 29 isolates from 8 other species. Geometric mean (GM) MIC values for all antifungals were significantly higher when tested at pH 4 (p < .001 for all comparisons). For C. albicans, the largest GM MIC differences were observed for terconazole (0.17 pH 7 vs 6.17 pH 4) and clotrimazole (0.04 vs 0.24). For terconazole, 97.7% of the isolates had a MIC of 1 or less at pH 7 but 83.2% had a MIC of 4 or higher at pH 4. For C. glabrata, terconazole (GM MIC = 0.26 pH 7 vs >64 pH 4), clotrimazole (0.13 vs 6.96), miconazole (0.06 vs 0.76), and fluconazole (3.17 vs 26.6) were most affected. All C. glabrata isolates had a MIC of 1 or less for terconazole at pH 7 and one had a MIC of 8 at pH 4, whereas all the rest were highly resistant (MIC > 64). Antifungals have reduced in vitro potency when tested at lower pH. Candida glabrata is more affected than C. albicans. The impact may be greatest for the antifungal terconazole and against C. glabrata isolates.

Chemical composition and antifungal potential of Iranian propolis against Candida krusei strains

Propolis is known to have biological properties against numerous microorganisms of clinical interest. This is important, because all Candida krusei (C. krusei) isolates are resistant to azole drugs. The aims of this study were to determine the chemical composition and antifungal efficacy of Iranian propolis against C. krusei strains isolated from patients with cutaneous and mucosal candidiasis. Ethanolic extract of propolis (EEP) was prepared from propolis originating from Mazandaran province, and submitted to chemical analysis by high-resolution gas chromatography coupled to mass spectrometry. Additionally, the EEP was tested for its ability to inhibit yeasts by determination of the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) using broth microdilution method (M27-A3 protocol) with some modifications. Phenolic acids (78.2%) were the major components of Iranian propolis. The EEP exhibited MIC values ranging from 2 to 20 mg/ml and MFC values between 4 and 25 mg/ml. The most fungal susceptibility was associated with the nail isolates (mean MIC value: 7.8 mg/ml), followed by the oral isolates (mean MIC value: 9.7 mg/ml) and vaginal isolates (mean MIC value: 11.7 mg/ml). The results showed that Iranian propolis has strong anti-C. krusei activity and should be considered as a promising candidate to treat nail, oral and vaginal candidiasis.

Reproducible measurement of vancomycin MICs within the susceptible range in Staphylococcus aureus by a broth microdilution method with a "quasi-continuum" gradient of antibiotic concentrations.

The availability of reproducible broth microdilution (BMD) methods including inter log2 antibiotic dilutions for measuring Staphylococcus aureus (SA) vancomycin minimum inhibitory concentrations (MICs) within the susceptible range is needed to elucidate the impact of vancomycin MICs on clinical outcomes of invasive SA infections. Here, we report on the development of a very precise BMD method that incorporates the following incremental antibiotic concentrations: 0.50, 0.62, 0.75, 0.87, 1.0, 1.25, 1.40, 1.50, 1.60, 1.75, and 2.0μg/mL. The intra- and inter-assay coefficients of variation of this method were around 20%. The mean of the differences in MIC values for all isolates obtained across two independent runs performed at one center was 0.04μg/mL [95% confidence interval (CI), 0.011-0.07μg/mL] and that for ten isolates measured at two different centers was 0.04μg/mL (95% CI, 0-13μg/mL). Vancomycin MIC values differed by less than 0.1μg/mL between runs for most isolates. Storage of isolates at -20°C for up to 3months had no impact on the vancomycin MIC values. The mean vancomycin MIC values obtained by the Etest using a standard inoculum (0.5 McFarland) were significantly higher (p≤ 0.001) than those measured by BMD and the MIC values measured by the two methods correlated poorly (Rho, 0.319; p=0.148). Nevertheless, the mean MIC values measured by the Etest using lower inocula (107 or 106CFU/mL) and those measured by BMD were comparable and correlated significantly (p=0.004 for 107CFU/mL and p=0.029 for 106CFU/mL).

Fungicidal efficacy of various honeys against fluconazole-resistant Candida species isolated from HIV+ patients with candidiasis

Honey is well known to possess a broad spectrum of activity against medically important organisms. The purpose of this study was to assess the antifungal activity of different honeys against 40 fluconazole (FLU) resistant Candida species, including Candida albicans (C.albicans), Candidaglabrata, Candidakrusei and Candidatropicalis. Three honey samples were collected from northern (Mazandaran, A), southern (Hormozgan, B) and central (Lorestan, C) regions of Iran. A microdilution technique based on the CLSI, M27-A2 protocol was employed to compare the susceptibility of honeys "A", "B" and "C" against different pathogenic Candida isolates. The results showed that different Candida isolates were resistant to FLU, ranging from 64μg/mL to 512μg/mL. All of the honeys tested had antifungal activities against FLU-resistant Candida species, ranging from 20% to 56.25% (v/v) and 25% to 56.25% (v/v) for minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs), respectively. Honey "A" (MIC: 31.59%, v/v) showed higher anti-Candida activity than honey "B" (MIC: 35.99%, v/v) and honey "C" (MIC: 39.2%, v/v). No statistically significant differences were observed among the mean MIC values of the honey samples (P>0.05). The order of overall susceptibility of Candida species to honey samples were; C.krusei>C.glabrata>C.tropicalis>C.albicans (P>0.05). In addition, the mean MICs of Candida strains isolated from the nail, vagina and oral cavity were 33.68%, 36.44% and 39.89%, respectively, and were not significantly different (P>0.05). Overall, varying susceptibilities to the anti-Candida properties of different honeys were observed with four FLU-resistant species of Candida. Further research is needed to assess the efficacy of honey as an inhibitor of candidal growth in clinical trials.

Investigation of Glycopeptide Susceptibility of Coagulase-Negative Staphylococci (CoNS) From a Tertiary Care Hospital in Gorgan, Northern Iran

Background: Coagulase-negative staphylococci (CoNS) are clinically important, especially in nosocomial and neonatal infections. The increasing emergence of glycopeptide-resistant CoNS has made these agents therapeutically challenging. Objectives: We aimed to investigate the susceptibility patterns of CoNS to teicoplanin and vancomycin in Gorgan, northern Iran. Materials and Methods: A total of 100 clinical samples were obtained from different wards of a hospital and screened for CoNS with standard microbiological and biochemical tests. Antibiogram testing was carried out for the detection of vancomycin-, teicoplanin-, and multidrug-resistant (MDR) species. The minimum inhibitory concentration (MIC) of vancomycin was determined using E-test strips. The presence of the vanA gene was investigated with PCR. Results: Only 1% of CoNS (Staphylococcus haominis) showed resistance to vancomycin and 15% of these were intermediate-resistant to teicoplanin on the disc diffusion agar test. In addition, all isolates (100%) were negative for vanA on PCR and sensitive with E-test methods. The mean MIC value of vancomycin was 1.35 ± 0.29 µg/mL. S. haemolyticus and S. epidermidis showed the highest rates of MDR (50% and 24%, respectively). Additionally, CoNS isolated from blood (42%) and urine samples (30%) had the highest rates of MDR. Conclusions: Vancomycin, but not teicoplanin, can be considered an effective antibiotic of choice for controlling infections caused by MDR CoNS in Gorgan, depending on the bacterial species.

Molecular identification andin-vitroantifungal susceptibility testing of Candida species isolated from patients with onychomycosis.

Background and Purpose: Candida species are the most opportunistic fungi affecting the nails and resulting in onychomycosis. In this study, we identified and evaluated in-vitro susceptibility of the recovered isolates against fluconazole (FLC), voriconazole (VRC), and clotrimazole (CLT) using the Clinical and Laboratory Standards Institute (CLSI) M27-A3 document.Materials and Methods:From patients with either clinically or mycologically proven onychomycosis, 97 isolates comprising of seven Candida species were isolated, which were identified by both conventional and molecular techniques such as polymerase chain reaction-restriction fragment length polymorphism. In addition, Candida dubliniensis was confirmed by restriction endonuclease analysis. Antifungal susceptibility of each isolate against the three azoles applied in this study was determined using the CLSI microdilution reference method M27-A3. Results: Candida parapsilosis (C. parapsilosis) was the most frequently isolated species (n=44), followed by C. albicans (n=23), C. tropicalis (n=13), C. glabrata (n=7), C. krusei (n=6), C. guilliermondii (n=3), and C. dubliniensis (n=1). All the isolates were susceptible to CLT. VRC had lower minimum inhibitory concentration (MIC) values for the isolates compared to FLC. Geometric mean MIC values of VRC, FLC, and CLT for C. parapsilosis isolates were 0.07 μg/ml, 0.8 μg/ml, and 0.35 μg/ml, respectively. Collectively, all species exhibited greater susceptibility to VRC in comparison to C. albicans (P≤0.001).Conclusion:This study showed that non-albicans Candida species were the most common etiologic agents of non-dermatophyte onychomycosis. The major antifungal agents used in clinics to empirically treat yeast onychomycosis are FLC and CLT. Our data suggested that CLT is a better choice for the treatment of Candida onychomycosis, especially in drug resistant cases.

Efficacy of Cuminum cyminum essential oil on FUM1 gene expression of fumonisin-producing Fusarium verticillioides strains.

The purpose of this study was to evaluate the effect of Cuminum cyminum (C. cyminum) essential oil on the growth and FUM1 gene expression of fumonisin-producing Fusarium verticillioides (F. verticillioides) strains isolated from maize. All fungal strains were cultured on potato dextrose agar (PDA) slopes at 30°C for 7 days. The antifungal activity was evaluated by broth microdilution assay. One set of primers was F. verticillioides species specific, which selectively amplified the intergenic space region of rDNA. The other set of primers was specific to FUM1 gene region of fumonisin-producing F. verticillioides. FUM1 transcript levels were quantified using a reverse transcription-polymerase chain reaction (RT-PCR) protocol. Minimum inhibitory concentration (MIC) values of C. cyminum oil against F. verticillioides strains varied from 0.195 to 0.781 µl.ml(-1) (mean MIC value: 0.461 µl.ml(-1)) indicating 54.5% of the fungal strains inhibited at 0.390 µl.ml(-1). PCR analysis of FUM1 gene expression revealed that DNA fragment of 183 bp was amplified in all the isolates of F. verticillioides before treatment with C. cyminum essential oil. Based on RT-PCR analyses, reduction in the expression of fumonisin biosynthetic genes was significant only for FUM1 gene (p<0.05), while no effect was observed on ITS gene. This study showed that all F. verticillioides isolates were susceptible to C. cyminum essential oil, indicating a significant reduction in the growth of fungal isolates. In addition, this oil completely inhibited the expression of FUM1 gene in concentrations dose-dependently.

An in vitro Evaluation of Antibacterial Activity of Curcumin against Aggregatibacter actinomycetemcomitans

ABSTRACT Introduction Development of bacterial resistance to the available antibiotics and increasing popularity of traditional medicine has led researchers to investigate the antibacterial compounds in plants. In this context, curcumin has been shown to have a range of beneficial properties, like antimicrobial and anti-inflammatory properties, which might be favorable for the treatment of inflammatory diseases like periodontitis. Aims and objectives The primary objective of this study was to evaluate the antibacterial potential of curcumin against Aggregatibacter actinomycetemcomitans (ATCC 29523). Materials and methods The bacterial strains of A. actinomycetemcomitans from the stock were revived and transferred to sterile brain heart infusion (BHI) broth. Minimum inhibitory concentration (MIC) was determined by serial broth dilution of curcumin. The last tube with clear supernatant was considered to be without any growth and taken as MIC value. Results The mean MIC value of curcumin against A. actinomycetemcomitans (ATCC 29523) was reported to be 0.2 μg/ml. Conclusion Thus, it can be concluded that the pleiotropic activities of curcumin derived from its complex chemistry and its ability to influence and control the multiple signaling pathways, makes it a suitable and safer option for the treatment of periodontal diseases. How to cite this article Savita AM, Dawra C, Bhat K. An in vitro Evaluation of Antibacterial Activity of Curcumin against Aggregatibacter actinomycetemcomitans. World J Dent 2015;6(1):16-19.

Evaluation of anti-microbial activity of spore powder of Ganoderma lucidum on clinical isolates of Prevotella intermedia: A pilot study.

Aim:This study aimed at evaluating the anti-microbial activity of spore powder of Ganoderma lucidum on Prevotella intermedia isolated from subgingival plaque from chronic periodontitis patients.Settings and Design:Written informed consent was obtained from each subject enrolled in the study. The Institutional Ethics Committee granted the ethical clearance for the study.Materials and Methods:This study included 20 patients diagnosed with chronic periodontitis. Pooled subgingival plaque samples were collected using sterile curettes from the deepest sites of periodontal pockets. The collected samples were then transported in 1 mL of reduced transport fluid. The organisms were cultured and confirmed. These organisms were then used for minimum inhibitory concentration (MIC) procedure.Statistical Analysis:Mean of the MIC value obtained was calculated.Results:Thirteen out of the 20 clinical samples were tested that showed sensitivity at various concentrations. Five samples showed sensitivity at all concentrations. Twelve samples showed sensitivity at 8 mcg/ml. Eleven samples showed sensitivity at 4 mcg/ml, 8 samples showed sensitivity at 2 mcg/ml, and 5 samples showed sensitivity even at 1 mcg/ml. Mean MIC value of G. lucidum spore powder for P. intermedia obtained was 3.62 mcg/ml.Conclusion:G. lucidum with its multipotential bioactivity could be used as an anti-microbial, in conjunction with conventional therapy in periodontal disease.

Antifungal efficacy of thymol, carvacrol, eugenol and menthol as alternative agents to control the growth of food-relevant fungi

This work is an attempt to examine the antifungal activity of thymol, carvacrol, eugenol and menthol against 11 food-decaying fungi. The susceptibility test for the compounds was carried out in terms of minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) using microdilution method in 96 multi-well microtiter plates. Results indicated that all compounds were effective to varying extents against various fungal isolates, with the highest efficacy displayed by carvacrol (mean MIC value: 154.5 μg/mL) (P<0.05). The incorporation of increased concentrations of all compounds to the media led to progressive and significant reduction in growth for all fungi. The most potent inhibitory activity of thymol, carvacrol, eugenol and menthol was found for Cladosporium spp. (MIC: 100 μg/mL), Aspergillus spp. (MIC: 100 μg/mL), Cladosporium spp. (MIC: 350 μg/mL), and Aspergillus spp. and Cladosporium spp. (MIC: 125 μg/mL), respectively. Thus, the application of these herbal components could be considered as a good alternatives to inhibit fungal growth and to reduce the use of synthetic fungicides.

Comparitive phytochemical Analysis and Resilience Pattern Exhibited by thyme and tea tree oil against Selected Poultry Isolates

The volatile oils of Melaleuca alternifolia (tea tree) and Thymus vulgaris (thyme), of the family Myrtaceae and Lamiaceae respectively, were asessed for antibacterial activity against different avian pathogens isolated from infected chickens which involved Escherichia coli, Staphylococcus aureus, S.epidermidis, S. carnosus and Salmonella gallinarum. The antimicrobial activity of both the oils was assessed by using disc diffusion, minimum inhibitory concentration (MIC) as well as minimum bactericidal concentration (MBC) method. Thyme oil exhibited higher activity than tea tree oil against all the pathogens. Mean inhibition zones, MIC and MBC values of bacterial strains varied from 19 and 34 mm, 0.03%- 0.15% to 0.07 - 0.3% respectively. GC-MS analysis of essential oil of thyme showed the presence of 13 components. The major components were carvacrol, thymol, terpinene-4-ol, α- Terpinene, carvacrol methyl ether. Tea tree oil showed the presence of 16 components upon GC-MS analysis. The major compounds were Limonene, γ -Terpinene, α- Terpinene, Cineol and α- Terpinolene. Since aromatic and medicinal plants produce a wide variety of volatile terpenes, hydrocarbons (aliphatic and cyclic) and their corresponding oxygenated isoprenoid derivatives and analogues, the bactericidal effect observed in this study may be attributed to these components. Therefore, these oils could be a source of pharmaceutical materials required for the preparation of new therapeutic and antimicrobial agents.

The Antibacterial Effect of Ethanol Extract of Polish Propolis on Mutans Streptococci and Lactobacilli Isolated from Saliva

Dental caries occurrence is caused by the colonization of oral microorganisms and accumulation of extracellular polysaccharides synthesized by Streptococcus mutans with the synergistic influence of Lactobacillus spp. bacteria. The aim of this study was to determine ex vivo the antibacterial properties of ethanol extract of propolis (EEP), collected in Poland, against the main cariogenic bacteria: salivary mutans streptococci and lactobacilli. The isolation of mutans streptococci group bacteria (MS) and Lactobacillus spp. (LB) from stimulated saliva was performed by in-office CRT bacteria dip slide test. The broth diffusion method and AlamarBlue assay were used to evaluate the antimicrobial activity of EEP, with the estimation of its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The biochemical composition of propolis components was assessed. The mean MIC and MBC values of EEP, in concentrations ranging from 25 mg/mL to 0.025 mg/mL, for the MS and LB were found to be 1.10 mg/mL versus 0.7 mg/mL and 9.01 mg/mL versus 5.91 mg/mL, respectively. The exposure to an extract of Polish propolis affected mutans streptococci and Lactobacillus spp. viability, exhibiting an antibacterial efficacy on mutans streptococci group bacteria and lactobacilli saliva residents, while lactobacilli were more susceptible to EEP. Antibacterial measures containing propolis could be the local agents acting against cariogenic bacteria.

In vitro antimicrobial effect of silver nanoparticles on Lactococcus garvieae and Streptococcus iniae

Antimicrobial effect of silver nanoparticles on two fish pathogens, Lactococcus garvieaeand Streptococcus iniae was investigated by microdilution method. A total of 16 isolates ofL. garvieae and S. iniae that were obtained from diseased rainbow trout during 2009 to 2011 were examined. Antimicrobial effects of the compound were evaluated according to the broth microdilution method by determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). According to the results MIC ranged from 1.12 to 5 µgml-1 for L. garvieae and 1.12 to 2.5 µgml-1 for S. iniae isolates. The mean MIC value was 2.59 and 2.1 for L. garvieae and S. iniae, respectively. The MBC was also calculated for the examined isolates as MBC ranged from 2.5 to 10 µgml-1 with the mean of 5.27 and 3.57 for L. garvieae and S. iniae, respectively. The results showed that S. iniaestrains were more sensitive to silver nanoparticles than L. garvieae strains. This study demonstrated the in vitro antimicrobial effects of silver nanoparticles on the examined bacteria although the efficacy of silver nanoparticles in fish ponds in different conditions needs more investigations. Key words: Silver nanoparticles, Lactococcus garvieae, Streptococcus iniae.

Antibiotic activity of tigecycline against clinical pathogens by the micro dilution method

Resistant pathogens are the cause of clinical infections which threatening the patients lives and challenging the health systems through their economic importance. Therefore, new antibacterial agents with a broader spectrum of activity that protect against development of resistance are required. Tigecycline (Tygacil, Wyeth) is a relatively new FDA and EMEA approved glycylcycline antimicrobial with an expanded broad-spectrum activity against pathogens involved in complicated skin and skin structure infections. In this study we evaluated the in vitro activity of tigecycline in comparison to 14 other antibiotics against 182 clinical pathogens by use of the micro dilution method. In overall, tigecycline exhibited the lowest Minimum Inhibitory Concentration (MIC) values in almost all bacteria with a mean of 0.52 ± 1.25 mg/L, followed by meropenem and levofloxacin (mean MIC values 1.29 ± 2.52 and 1.45 ± 3.078 mg/L, respectively). MIC50 and MIC90 values of tigecycline were: 0.06 and 0.15 mg/L for E. coli, 0.12 and 1.00 mg/L for Klebsiella sp., 0.12 and 0.85 mg/L for various Enterobacter sp., 1.00 and 8.00 mg/L for Pseudomonas sp., 0.25 and 1.00 mg/L for Acinetobacter sp., 0.06 and 0.12 mg/L for Serratia sp., 0.12 and 0.25 mg/L for Staphylococcus aureus, 0.5 and 5.00 mg/L for Streptococcus sp. The MIC values recorded were among the lowest in recent literature for Acinetobacter sp. (included A. baumannii), and comparable to those obtained for Klebsiella, Serratia and Enterobacter indicating that tigecycline has a promising in vitro activity.

Antibacterial activity of five oil bearing Ethiopian medicinal plants against eleven pathogenic bacterial strains

The antibacterial activity of volatile fractions from Artemesia abyssinthium, Croton macrostachyus, Echinops kebericho and Satureja punctata has been tested against selected Gram-positive and Gram-negative bacterial strains. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of five essential oils were investigated for their antibacterial activities against four gram-positive (Staphylococcus aureus (ATCC 25923), Streptococcus pyogenes, Listeria monocytogenes and Bacillus cereus) and seven gram-negative (Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Salmonella paratyphi, Shigella dysenteriae, Citrobacter sp., Klebsiella pneumonia and Proteus mirabilis) bacterial species. All the essential oils were active against all tested bacterial species. L. monocytogenes, B. cereus, and S. aureus were the three most sensitive bacteria with a mean concentration of 0.14, 0.8 and 0.62µg/ml, respectively. Almost all the essential oils have shown least activities against L. monocytogenes. In contrast, antibacterial activities were highest against S. paratyphi, P. mirabilis and E. coli with a mean concentration of 20.8, 18.8 and 15.7µl/ml, respectively. P. aeruginosa was found to be the most sensitive bacteria to all essential oils showing MIC of 0.1 to 1.6 with overall mean values of 0.62µl/ml while K. pneumonia ranked next with MIC mean values of 1.36µl/ml. The mean MIC values of the essential oils against B. cereus were significantly higher than the control (P= 0.013) whereas the essential oils against L. monocytogenes and S. aureus had comparable antibacterial activity with the control drug (P>0.05). The mean of MIC values were significantly higher against Gram-positive than Gram-negative bacteria (P<0.001).

Antibacterial Activity Against FoodborneStaphylococcus aureusand Antioxidant Capacity of Various Pure Phenolic Compounds

Six pure phenolic compounds (hydroquinone, thymol, carvacrol, butylated hydroxyanisole, gallic acid, and octyl gallate) were tested for their minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against several strains of Staphylococcus aureus isolated from dairy and meat products. In addition, S. aureus reference strains (American Type Culture Collection) for antimicrobial studies and/or isolated from human infections and outbreaks of food poisoning were included in the study. Of the compounds tested, octyl gallate and hydroquinone were the most effective against S. aureus (mean MIC values of 20.89 and 103.05 μg/mL, respectively) and carvacrol and thymol the least (mean MIC values of about 413 μg/mL). The mean MBC values were 40.84, 194.37, 417.46, and 581.90 μg/mL for octyl gallate, hydroquinone, carvacrol, and thymol, respectively. Meat isolates were more resistant than those of dairy origin to hydroquinone, gallic acid, and octyl gallate, as well as to penicillin G (used as a control of the methodology used); gallic acid and penicillin G showed the highest differences in MIC values between the groups of strains (about 10 and 200 times, respectively). On the other hand, when we tested the isolates included in each group of strains (dairy, meat, and other/mixed sources) we only detected significant differences (p < 0.05) among dairy and isolates from other/mixed sources for hydroquinone and thymol, respectively. However, strains of meat origin exhibited significant differences among each other (p < 0.05) to most of the phenolic compounds tested (hydroquinone, carvacrol, gallic acid, and octyl gallate). The relationship between MICs and MBCs for each of the phenolic compounds tested suggested a bactericidal mechanism of action against S. aureus. Gallic acid and octyl gallate exhibited the highest antioxidant capacity and thymol and carvacrol the lowest. So, octyl gallate is an agent with both antimicrobial and antioxidant properties, which would be of interest to use in the food industry.