Maximum Minimum Inhibitory Concentration Research Articles

Utilizing intramammary Melaleuca alternifolia as an organic internal sealant for dry-off therapy in Murrah buffaloes.

The effects of intramammary dry cow therapy based on the administration of 5% Melaleuca alternifolia tea tree essential oil (TTO) as an internal teat sealant to Murrah cows were evaluated. A longitudinal prospective and retrospective negative control study was performed using 12 buffaloes from a total of 20 Murrah buffaloes on an organic farm, with the cow used as a control for herself. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for treatments with pure oil (TTO) and medication containing 5% TTO (O5) were determined. The buffaloes were clinically examined, and the teats were evaluated using thermography and ultrasound. Udder health was monitored during the first 100days in milk (DIM) using milk somatic cell count (SCC) and California mastitis test (CMT). Laboratory tests against standard strains Staphylococcus aureus ATCC®25,923™, Escherichia coli ATCC®25,922™, and wild bacterial strains showed maximum MIC values of 50 µL/mL for the TTO and O5 treatments. One wild-type S. aureus strain showed no MBC. No adverse effects were observed after the intramammary application of TTO. The CMT and SCC values were similar (P > 0.05) for all observations. The medication containing 5% TTO was effective in vitro and compatible with the intramammary tissue in vivo of Murrah buffaloes. TTO was safe, not inducing inflammatory processes or other modifications of the teat detectable by thermography or ultrasound. It was able to protect buffaloes during the dry period under field conditions, demonstrating potential use as a teat sealant for organic farms.

Synthesis and Characterization of Novel Hydrazone Derivatives of Isonicotinic Hydrazide and Their Evaluation for Antibacterial and Cytotoxic Potential.

Hydrazones are active compounds having an azomethine –NHN=CH group and are widely studied owing to their ease of preparation and diverse pharmacological benefits. Novel isonicotinic hydrazone derivatives of vanillin aldehyde and salicyl aldehyde were synthesized that had azomethine linkages and were characterized by UV–Visible, FTIR, EI-MS, 1H-NMR and 13C-NMR spectroscopy. The compounds were screened for their antibacterial activity against Staphylococcus aureus, Bacillus subtilus, and Escherichia coli using disc diffusion and minimum inhibitory concentration (MIC) methods. For cytotoxicity, a brine shrimp lethality test was performed to calculate the lethal concentration (LC50). The results demonstrated appreciable antibacterial activities against the applied strains, amongst which the compounds coded NH3 and NH5 showed maximum inhibition and MIC responses. In terms of cytotoxic activity, the maximum effect was observed in compound NH5 and NH6 treatments with minimum survival percentages of 36.10 ± 3.45 and 32.44 ± 2.0, respectively. These hydrazones could be potential candidates in antitumorigenic therapy against various human cancer cells.

Antibiotic and metal resistance of Stenotrophomonas maltophilia isolates from Eboling permafrost of the Tibetan Plateau.

Whole-genome sequencing of pathogenic bacteria Stenotrophomonas maltophilia from a less polluted environment of permafrost can help understand the intrinsic resistome of both antibiotics and metals. This study aimed to examine the maximum minimum inhibitory concentration (MIC) of both antibiotics and metals, as well as antibiotic resistance genes and metal resistance genes annotated from whole-genome sequences. The permafrost S. maltophilia was sensitive to ciprofloxacin, tetracycline, streptomycin, and bacitracin, and resistant to chloramphenicol, trimethoprim-sulfamethoxazole, erythromycin, Zn2+, Ni2+, Cu2+, and Cr6+, with a lower maximum MIC, compared with clinical S. maltophilia. The former strain belonged to the lower antibiotic resistance gene (ARG) and metal resistance gene (MRG) clusters compared with the latter ones. The permafrost strain contained no or only one kind of ARG or MRG on a single genomic island, which explained the aforementioned lower maximum MIC and less diversity of ARGs or MRGs. The result indicated that the co-occurrence of antibiotic and metal resistance was due to a certain innate ability of S. maltophilia. The continuous human use of antibiotics or metals induced selective pressure, resulting in higher MIC and more diverse ARGs and MRGs in human-impacted environments.

In-vitro antibacterial activity of commercially available probiotics on food-borne pathogens along with their synergistic effects with synthetic drugs

BackgroundProbiotics are put forward as food to ensure the maintenance of the equilibrium of the intestinal flora. Prolonged usage of probiotics in food ingredients for human as well as in animal feed has not exposed any side effects yet. Present study attempted to justify the effects of some commercially available probiotics (Good-gut, Lubenna, Probio and Protein restro) and commonly used antibiotics (Streptomycin, Gentamycin, Ampicillin, Methicillin, Azithromycin, Erythromycin, Ceftrizone, Imepenem, Ciprofloxacin and Tetracycline) on the bacteria which were previously isolated from food samples. MethodsThe anti-bacterial potential of the probiotics was aimed to be checked through the agar well diffusion method and the antibiogram of the synthetic drugs was determined by disc-diffusion method (Kirby Bauer technique). The minimum inhibitory concentration (MIC) of the probiotics were examined through broth micro dilution assay. ResultsAlmost all the probiotic samples exhibited antibacterial activity against the tested bacteria within the range of 10 mm–30 mm except Bacillus spp. and Salmonella spp. The lowest MIC values 3 mg/ml was determined with Luvena for Pseudomonas spp. and Shigella spp. while the maximum MIC 20 mg/ml was recorded for Good gut and Probio against Salmonella spp. and E. coli. Meanwhile, majority of the tested pathogens were detected to be resistant against more than one antibiotic as MDR strains except gentamycin, streptomycin and azithromycin. During the combination method, the zone diameter increased remarkably with a clear indication of synergistic effects compared to their individual activity. ConclusionThis study substantiated that the deployment of a combination of two antibacterial medications in order to combat the multi-drug resistant bacteria would rather be efficacious than the application of either antimicrobial agent alone.

Chemical Analysis and Antioxidant and Antimicrobial Activity of Essential oils from Artemisia negrei L. against Drug-Resistant Microbes

BackgroundArtemisia negrei L. (A. negrei) is a medicinal and aromatic plant belonging to the family Asteraceae that is more widespread in the folded Middle Atlas Mountains, Morocco. Materials and Methods This study was run to investigate the phytochemical composition and antioxidant, antibacterial, and antifungal activities of Artemisia negrei L. essential oil. This oil was extracted from the fresh plant material by using the Clevenger apparatus. The phytochemical composition was characterized by GC-MS. The antioxidant activity was evaluated using different methods including DPPH, β-carotene bleaching, and total antioxidant capacity. The antibacterial activity was tested vs. multidrug-resistant bacteria including both Gram-negative and Gram-positive using inhibition zones in agar media and minimum inhibitory concentration (MIC) bioassays. The antifungal activity was conducted on Candida albicans, Aspergillus niger, Aspergillus flavus, and Fusarium oxysporum using a solid medium assay. Results The chromatographic characterization of essential oils of A. negrei revealed the presence of 34 compounds constituting 99.91% of the total essential oil. The latter was found to have promising antioxidant activity by all bioassays used such as DPPH, β-carotene bleaching, and total antioxidant capacity. The results obtained showed that our plant oils had potent antibacterial activity towards Gram-negative (E. coli 57, E. coli 97, K. pneumonia, and P. aeruginosa) and Gram-positive (S. aureus), so that the maximum inhibition zones and MIC values were around 18–37 mm and 3.25 to 12.5 mg/mL, respectively. The oil also showed antifungal activity towards Candida albicans, Fusarium oxysporum, and Aspergillus Niger except for flavus species. Conclusion The findings obtained in the work showed that A. negrei can serve as a valuable source of natural compounds that can be used as a new weapon to fight radical damage and resistant microbes.

Chemical Composition and Antimicrobial Activity of Oleoresin of Capsicum annuum Fruits

Capsicum annuum is consumed as a part of human diet since prehistoric period. The present study was designed to analyze the composition of oleoresin of C. annuum fruits and evaluate its antimicrobial potential. Study involved extraction of oleoresin by percolation of the pulverized dried ripe fruits, which were further analyzed using GC/GC-MS and evaluated for antimicrobial activity using standard disc diffusion method. The predominant constituents in capsicum oleoresin included linoleic acid (33.81%), 2,3-dihydroxypropyl oleate (16.80%), palmitic acid (15.57%), capsaicin (10.28%), and dihydrocapsaicin (6.09%). The capsicum oleoresin exhibited significant antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Candida albicans and Aspergillus niger. Antimicrobial potential of C. annuum oleoresin was based on determination of zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) through disk diffusion method. Oleoresin exhibited maximum ZOI and MIC against B. subtilis (12.0±0.5 mm and 25 μL/mL) and A. niger (30.0±0.5 mm and 40 μL/mL). This study concluded capsicum oleoresin to contain large number of fatty acids and their esters, amides, monoterpenes, diterpenes, triterpenes, sesquiterpenes, and phytosterols. It also exhibited significant antimicrobial activity against pathogenic microorganisms.

In Vitro Antibacterial Effectiveness of a Naturopathic Oral Care Product on Oral Pathogens.

Currently, the prevention of periodontal diseases focuses on mechanical removal of pathogenic biofilms combined with oral antiseptics as supportive chemical antibacterial control. Due to the risk of resistance development and side effects of existing antiseptics, the interest in alternative medicine with naturopathic treatment modalities is growing in dentistry. In the present study, the antibacterial effect of the naturopathic oral care product Repha OS and some of its derivatives, based on medicinal plant extracts and essential oils, with a specific focus on added sweeteners, was investigated on periodontal pathogenic and halitosis-associated bacteria. The antibacterial efficacy was investigated by agar dilution assay. The minimum inhibitory concentration (MIC) for the bacterial species Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia and Solobacterium moorei was determined. A concentration-dependent antibacterial effect on oral bacterial species by Repha OS and its derivatives was demonstrated. For the original product, the maximum MIC was 10% of the calculated test solution concentration in agar for all examined bacterial species. The removal of essential oils reduced the antibacterial efficacy, whereas the displacement or replacement of sweeteners had almost no effect. In addition to other individual effects of the ingredients, the results of this study show that an antibacterial effect of the naturopathic oral care product on the tested oral bacterial species was achieved in vitro. In vivo, the combination of this antibacterial effect with other properties of the various ingredients may be interesting for a holistic approach in preventive dentistry.

Occurrence of heavy metal resistance in Sinorhizobium sp. isolated from root nodules of fenugreek, treated with tannery effluent

The aim of present study was to initiate preliminary work on heavy metal contamination in farm soil (contaminated with processed tannery effluent) and its potential influence on the development of metal resistance among N2fixing bacterium, Sinorhizobium sp. Contaminated plant samples were analyzed for various metals and minimum inhibitory concentration (MIC) of metals was determined. Fenugreek (Trigonella sp.) plants revealed accumulation of these metals in root and leaves. Sinorhizobium sp. were isolated (25) from the root nodules of fenugreek-treated with processed tannery wastewater and characterized morpho-biochemically. All isolates were evaluated for their resistance against Cr3+, Cr6+, Cd2+, Cu2+, Zn2+ and Ni2+. The maximum MIC of 1600 μg mL−1 was noticed against Cr3+ in 64% isolates. Among all the isolates, the lowest MIC of 25 μg mL−1 was detected against Ni2+. Some metal resistant isolates were evaluated for their resistance against frequently used antibiotics viz., tetracycline, ampicillin, gentamycin, kanamycin, chloramphenicol and nalidixic acid. About 46% Sinorhizobium isolates were resistant to nalidixic acid whereas 26.6% showed resistance to ampicillin and kanamycin. The isolates demonstrated confluent growth upto a salt concentration of 3%; whereas isolates (SM17, SM24) tolerated 10% NaCl. Acidic pH eliminated almost all the test population and neutral pH had no suppressive effect on growth while majority were tolerant to pH 9.

Synthesis and Characterization of Novel Azole Functionalized Poly(glycidyl methacrylate)s for Antibacterial and Anticandidal Activity.

Presently, rise in the infectious diseases and subsequent development of drug resistance, is a global threat to human health. However, much efforts are being made by scientists, to develop novel antimicrobials, and also to improve the efficacy of available drugs, in order to combat the lifethreatening infections. Synthesis and characterization of azole functional polymer systems for antimicrobial applications. Poly(glycidyl methacrylate) (PGMA), was produced by free radical polymerization of the monomer, glycidyl methacrylate (GMA). Different azole functional PGMAs were produced, through chemical modification with imidazole (Im), 1H-1,2,4-triazole (Tri) and 3-amino-1,2,4-triazole (ATri), to get PGMA-Imi, PGMA-Tri and PGMA-ATri, respectively. The structure was confirmed by Fourier transform infrared spectroscopy (FT-IR), thermal properties were investigated by Thermogravimetric Analysis (TGA), and surface morphology was studied by scanning electron microscopy (SEM). Newly synthesized derivatives were further explored, for their antibacterial and anticandidal activities. All the three synthesized and characterized derivatives, displayed a significant activity against the tested microorganisms. The minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC), recorded against Staphylococcus aureus (S. aureus), was 0.5 &1mg/ml for PGMA-Imi, followed by PGMA-ATri & PGMA-Tri, respectively, followed by E. coli with, 1 & 2 mg/ml, 4 & 8 mg/ml, 4& 8 mg/ml, respectively, whereas the maximum MIC & MFC was recorded against C. albicans i.e., 8 & 16 mg/ml, 4 & 8 mg/ml ,4 & 8 mg/ml for PGMA-ATri, PGMA-Tri, PGMA-Imi, respectively. In the present work, we report on the state-of-the-art, azole functional polymer systems for antimicrobial applications. These findings suggest that the synthesized azole functional polymer films have antimicrobial properties, which could be potential candidates for coating applications in the biomedical and wastewater treatment field.

Antibacterial activity of different composition of aglycone and glycosidic saponins from tuber of Cyclamen coum Miller

Many plants biosynthesize biochemical compounds with antibacterial properties that can be used in industrial or food technology. They have effect on growth of bacteria thus, natural constituents in the plant extracts open new trends to control microbial infections. Cyclamen is a wild plant that can be used as a drug. Aim of this work is to reveal antibacterial activity of the cyclamen tuber extracts and to determine its effective concentration against five different bacteria. Crude and hydrolyzed extracts of Cyclamen coum tuber were prepared by soxhlet and the extracts were separated to more polar and less polar phases via fractional solvents. After that, antibacterial impact of the extracts was investigated using disk diffusion method and it was determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The results showed that the extracts of Cyclamen coum were relatively rich in saponin but poor in phenolic compounds. The most antibacterial effect of n-butanolic saponin extracts were assayed against E. faecalis (PTCC 1393), which contained 0.87 μg saponin and resulted 16.6 mm diameter of inhibition zone. Furthermore, aqueous part of the aglycone extract with 0.08 μg total saponin revealed higher activity on P. aeruginosa (ATCC 1430) with 14 mm inhibition zone. Ethyl acetate phase of the aglycone extract with 0.2 μg of total saponin, showed 9.3 and 13.6 mm diameter of inhibition zone only against P. aeruginosa and S. aureus (ATCC 1431), respectively. Other extracts showed 7–13 mm inhibition zone, which was less effective. In addition, MIC n-butanolic extract was 0.4- 0.86 mg total saponin/mL whereas MIC of aqueous glycoside was 0.05- 0.86 mg saponin/mL. However, the later extract had no any bactericidal and bacteriostatic effect against S. aureus and E. faecalis. MIC and MBC of the ethyl acetate extract were 0.05 mg saponin/mL against clinical S. typhi whereas its MIC and MBC on P. aeruginosa and E. faecalis were 0.2 mg saponin/mL. Maximum MIC and MBC of the aqueous aglycone extract was assayed with 0.007 mg saponin/mL on clinical S. typhi, and MIC of 0.01 mg saponin/mL was estimated on S. aureus. Consequently, saponin tuber extracts of Cyclamen coum could be used as moderate to strong antimicrobial substance against gram-negative bacteria.

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.

Resistotyping, phenotyping and genotyping of New Delhi metallo-β-lactamase (NDM) among Gram-negative bacilli from Iranian patients.

The purpose of this study was to investigate New Delhi metallo-β-lactamase (NDM) production among Gram-negative bacilli. Antibiogram-resistotyping and detection of New Delhi metallo-β-lactamase (NDM) in clinical isolates of Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa and comparative evaluation of the diagnostic performance of three phenotypic methods for NDM detection, with PCR considered as the gold standard, were performed. Minimum inhibitory concentration (MIC) of antibiotics against NDM-positive strains using E-tests and clonal relationship analysis using enterobacterial repetitive intergenic consensus (ERIC)-PCR in these strains were determined. The most effective antibiotics against strains of the species K. pneumoniae were Colistin, Chloramphenicol and Tigecycline; against P. aeruginosa were Fosfomycin and Polymyxins, and against A. baumannii were Polymyxins, Ampicillin/Sulbactam and Minocycline. Overall, 66, 31 and 40 different resistotypes were observed among K. pneumoniae, A. baumannii and P. aeruginosa strains, respectively. The blaNDM-1 gene was detected in 28 (8.5 %) strains of the bacteria investigated. The sensitivities and specificities of the Meropenem-EDTA combined disk test, the meropenem-dipicolinic acid combined disk test and the modified Hodge test methods for NDM detection were 96.43, 55.15; 96.43, 54.85; and 89.29, 35.15, respectively. Additionally, in spite of the low positive predictive values of these tests, their negative predictive values were high. ERIC-PCR results revealed two main clusters in NDM-positive strains of each of the species P. aeruginosa and A. baumannii, and ten main clusters in K. pneumoniae. In all the NDM-positive strains maximum MIC rates (>256) were observed for all beta-lactam antibiotics. There were high levels of antibiotic resistance and a high frequency of multi-drug resistance and extensive-drug resistance profiles, as well as highly prevalent blaNDM-1 genes in the bacteria investigated.

Antimicrobial Activities of Fidaxomicin

Fidaxomicin is bactericidal against Clostridium difficile. The combined results of 8 in vitro studies of 1323 C. difficile isolates showed the minimum inhibitory concentration (MIC) range of fidaxomicin to be ≤0.001–1 μg/mL, with a maximum MIC for inhibition of 90% of organisms (MIC90) of 0.5 μg/mL. Isolates from 2 phase III clinical trials demonstrated that fidaxomicin MICs of baseline isolates did not predict clinical cure, failure, or recurrence of C. difficile infections. No resistance to fidaxomicin developed during treatment in either study, although a single strain recovered from a cured patient had an elevated MIC of 16 µg/mL at the time of recurrence. For 135 strains, OP-1118, a major metabolite, had an MIC for inhibition of 50% of organisms of 4 μg/mL and an MIC90 of 8 μg/mL. Changes in inoculum size (102–105 colony-forming units/spot) or cation concentrations of calcium or magnesium appeared to have no effect on fidaxomicin MICs. Fidaxomicin has little or no activity against gram-negative aerobes and anaerobes or yeast.

In vitro antifungal activities of essential oil from Nigerian medicinal plants against toxigenic Aspergillus flavus

The aim of this study is to determine the sensitivity profile of toxigenic mould strain isolated from poultry feed to some essential oils. Essential oils extracted from eight medicinal plants collected from South-West Nigeria were screened for their activity against toxigenic Aspergillus flavus by disc diffusion method. Minimum inhibitory concentrations (MICs) of oils (%v/v) against A. flavus done by agar dilution method and minimum fungicidal concentration (MFCs) data (%v/v) obtained by the broth micro dilution method. Different concentrations of the essential oils were also tested for spore germination of the assayed mould strains. In addition, the essential oils were able to inhibit the mould spores germination when assayed at different concentrations. The results showed that the maximum antifungal activity, MIC and reduction in spore germination was demonstrated by oils of Cymbopogon citratus, Allium sativum and Ocimum basilicum as compared to control, which showed activity similar to control (miconazole nitrate). The essential oils of Zingiber officialis, Citrus limon and Citrus aurantifolia exhibited moderate activity. The oils of Citrus sinensis demonstrated comparatively low activity against the isolate as compared to control while the oil of Pimenta racemosa did not show any activity against the isolate. These results support the plant oils can be used to cure infections caused by toxigenic A. flavus and plant oils may have role as pharmaceutical and preservatives.

Pharmacokinetics of tildipirosin in porcine plasma, lung tissue, and bronchial fluid and effects of test conditions on in vitro activity against reference strains and field isolates of Actinobacillus pleuropneumoniae

The pharmacokinetics of tildipirosin (Zuprevo(®) 40 mg/mL solution for injection for pigs), a novel 16-membered-ring macrolide for the treatment for swine respiratory disease (SRD), was investigated in studies collecting blood plasma and postmortem samples of lung tissue and bronchial fluid (BF) from swine. In view of factors influencing the in vitro activity of macrolides, and for the interpretation of tildipirosin pharmacokinetics in relation to minimum inhibitory concentrations (MIC), additional experiments were conducted to study the effects of pH, carbon dioxide-enriched atmosphere, buffers, and serum on tildipirosin MICs for various reference strains and Actinobacillus (A.) pleuropneumoniae field isolates. After single intramuscular (i.m.) injection at 4 mg/kg body weight, maximum plasma concentration (Cmax) was 0.9 μg/mL observed within 23 min (Tmax ). Mean residence time from the time of dosing to the time of last measurable concentration (MRTlast) and terminal half-life (T1/2) both were about 4 days. A dose-response relationship with no significant sex effect is observed for area under the plasma concentration-time curve from time 0 to the last sampling time with a quantifiable drug concentration (AUClast) over the range of doses up to 6 mg/kg. However, linear dose proportionality could not be proven with statistical methods. The time-concentration profile of tildipirosin in BF and lung far exceeded that in blood plasma. In lung, tildipirosin concentrations reached 3.1 μg/g at 2 h, peaked at 4.3 μg/g at day 1, and slowly declined to 0.8 μg/g at day 17. In BF, tildipirosin levels were 14.3, 7.0, and 6.5 μg/g at days 5, 10, and 14. T1/2 in lung was ∼7 days. Tildipirosin is rapidly and extensively distributed to the respiratory tract followed by slow elimination. Culture media pH and carbon dioxide-enriched atmosphere (CO2 -EA) had a marked impact on in vitro activity of tildipirosin in reference strains of various rapidly growing aerobic and fastidious bacteria including Histophilus (H.) somni ATCC 700025 and A. pleuropneumoniae ATCC 27090. For A. pleuropneumoniae ATCC 27090 testing conditions without CO2 -EA resulted in reduced acidification of culture media pH and a reduction in the minimum inhibitory concentrations compared to standard in vitro test conditions by 2 log2 dilution steps (4-fold) from 8 to 2 μg/mL. Supplementary buffering of standard culture media resulted in a reduction in the A. pleuropneumoniae (n = 8) MIC range by 4 log2 dilution steps (16-fold) from 8-16 to 0.5-1 μg/mL. Incremental supplementation of culture media with 50% serum resulted in noticeable shifts to lower minimum or maximum MICs by at least 2 log2 dilution steps (≥4-fold) in all aerobic and fastidious reference strains tested except for Pasteurella (P.) multocida. The MIC of A. pleuropneumoniae ATCC 27090 decreased by 2-4 log2 dilution steps (4 to 16-fold) from 8 to 0.5-2 μg/mL when 50% serum was added to the standard assay. Considering a higher presence of serum and the rather neutral pH conditions maintained in vivo, it is suggested to take the influence of these factors on in vitro activity into account when interpreting tildipirosin MICs for A. pleuropneumoniae in relation to pharmacokinetics.

Investigation of bioremediation of arsenic by bacteria isolated from contaminated soil

The aims of this study are isolating arsenite-resistant bacteria from arsenic contaminated soil and the investigation of arsenite bioremediation efficiency by the most resistant isolates. Isolation of arsenite-resistant bacteria and the minimum inhibitory concentration (MIC) were conducted by spread plate method and the agar dilution method on PHG-II agar plates supplemented with sodium arsenite respectively. The results showed that, 69 and 25% of arsenite resistant isolates were geram positive and negative bacilli, respectively. Its maximum MIC was 128 mM/L, which is related to such bacteria asBacillus macerans, Bacillus megaterimand Corynebacterium vitarumen. There is a significant difference (P< 0.01) between three isolates in arsenite removal potential and arsenite bioaccumulation. The maximum percentage of arsenite removal potential (92%) and arsenite bioaccumulation (36%) were related to B. macerans. The removal efficiency of arsenite for B. macerans, C. (vitaromen) and B. megaterim were 60, 43 and 38% after 48 h of growth, respectively, while after 144 h of Bacillus macerans, Corynebacterium(vitaromen) growth and 120 h of Bacillus megaterimgrowth were 92, 80 and 73% respectively. The results also were shown the highest percentage of arsenite in biomass (36%), arsenate from oxidation (27%) were related to B. macerans, B. megaterium and B. megaterium. These results express the probability of finding more arsenic accumulating bacteria from the contaminated soil environment and can be concluded that arsenic resistant and/or accumulating bacteria, such as Bacillus sp., are widespread in the polluted soils and are valuable candidates for bioremediation of arsenic contaminated ecosystems. Key words: Arsenite, bacteria, bioremediation, MIC.

Antibiotic resistance profiles of representative wetland bacteria and faecal indicators following ciprofloxacin exposure in lab-scale constructed mesocosms

In this study, the effect of the antibiotic ciprofloxacin on the presentation and potential development of antibiotic resistance among selected faecal indicators ( Escherichia coli and Enterococcus spp.) and the intrinsic bacterial community for a freshwater model ecosystem was investigated. Four parallel mesocosm wetlands planted with Phragmites australis were initially seeded with an activated sludge inoculum from a wastewater treatment plant and monitored over the course of 63 days. Two of the four mesocosms (CIP1 and CIP2) were initially exposed to a ciprofloxacin concentration of 2 μg mL −1 for a 5 day period, and two were considered controls (CON1 and CON2). Minimum inhibitory concentrations were determined for the culturable interstitial microbial community using ciprofloxacin concentrations ranging from 0.5 to 16 μg mL −1 and compared with total heterotrophic plate counts (HPCs). E. coli and Enterococcus spp. were enumerated and screened for antimicrobial resistance to twelve different antibiotics both before and after mesocosm ciprofloxacin exposure. Concentrations for total heterotrophs within the interstitial water were in the order of 10 6–10 8 CFU 100 mL −1, while E. coli and Enterococcus spp. were present in lower concentrations, at 10 2–10 3 CFU 100 mL −1. All four mesocosms had the same minimum inhibitory concentrations (MICs) of 2 μg mL −1 for total heterotrophic community during the first week of start-up (before ciprofloxacin exposure), followed by a sharp increase in ciprofloxacin exposed mesocosms on day 14 (after ciprofloxacin exposure), reaching a maximum MIC of 16 μg mL −1. The resistance levels of interstitial heterotrophic counts determined by the agar dilution method peaked 7 days following the ciprofloxacin exposure, and decreased thereafter. A significant increase ( p < 0.05) to the following antibiotics was observed among E. coli following ciprofloxacin exposure within mesocosm CIP2: ciprofloxacin (CIP), chloramphenicol (C), cefotaxime (CTX), ceftriaxone (CRO), and doxycycline (D). These results illustrate the potential for a single antibiotic exposure event to create a noticeable increase in the antibiotic resistance profile, not only to the imposed antibiotic, but to other classes of antibiotics. The initial background levels of resistance among Enterococcus spp. were significantly higher than those observed among E. coli, exhibiting a combined average of 96%, 96%, and 100% resistance to ciprofloxacin (CIP), linezolid (LZD), and streptomycin (S), respectively. Following the addition of ciprofloxacin, Enterococcus spp. retained high levels of resistance to ciprofloxacin, linezolid, and streptomycin, with a significant increase ( p < 0.05) to vancomycin (VA), reaching 100% on Day 63. The findings of this study suggest that the transient presence of an isolated exposure event of ciprofloxacin can impact the antibiotic resistance profiles among faecal indicators in lab-scale constructed mesocosms and has the potential to impact constructed wetland treatment systems.

Tracking changes in the vraSR and graSR two component regulatory systems during the development and loss of vancomycin non-susceptibility in a clinical isolate

We investigated changes in regulatory genes, vraS and graR, during development of vancomycin non-susceptibility in a patient with methicillin-resistant Staphylococcus aureus who failed therapy and following in-vitro vancomycin exposure and a subsequent drug-free growth period. Minimum Inhibitory Concentration (MICs) were determined and genes sequenced at each stage. After 30 days of vancomycin exposure, the strain attained maximum MIC (20 mg/L) and was resistant to all antibiotics. Reversion to vancomycin susceptibility occurred 21 days after removal. We observed mutations in vraS and graR during non-susceptibly development and novel stop codons in the reverted strain. Mutations in graR appear important for development of intermediate susceptibility to vancomycin. The results suggest that monitoring of vancomycin therapy could allow earlier change to appropriate agents.

Incidence of metal and antibiotic resistance in Pseudomonas spp. from the river water, agricultural soil irrigated with wastewater and groundwater

A total of 144 isolates of Pseudomonas spp. (48 each from the Yamuna River water, wastewater irrigated soil and groundwater irrigated soil) were tested for their resistance against certain heavy metals and antibiotics. Minimum inhibitory concentrations (MICs) of Hg(2+ ), Cd(2+ ), Cu(2+ ), Zn(2+ ), Ni(2+ ), Pb(2+ ), Cr(3+ ) and Cr(6+ ) for each isolate were also determined. A maximum MIC of 200 μg/ml for mercury and 3,200 μg/ml for other metals were observed. The incidences of metal resistance and MICs of metals for Pseudomonas isolates from the Yamuna water and wastewater irrigated soil were significantly different to those of groundwater irrigated soil. A high level of resistance against tetracycline and polymyxin B (81.2%) was observed in river water isolates. However, 87.5% of Pseudomonas isolates from soil irrigated with wastewater showed resistance to sulphadiazine, whereas 79.1% were resistant to both ampicillin and erythromycin. Isolates from soil irrigated with groundwater exhibited less resistance towards heavy metals and antibiotics as compared to those of river water and wastewater irrigated soil. Majority of the Pseudomonas isolates from water and soil exhibited resistance to multiple metals and antibiotics. Resistance was transferable to recipient Escherichia coli AB2200 strains by conjugation. Plasmids were cured with the curing agent ethidium bromide and acridine orange at sub-MIC concentration.

Étude in vitro de la sensibilité au posaconazole de souches de Scytalidium spp. isolées de lésions superficielles

Scytalidium spp. is a dematiaceous fungi that has been frequently reported from tropical to semi subtropical regions. We distinguish two pathogenic species: S. dimidiatum and S. hyalinum which is an homologous non-pigmented mutant of S. dimidiatum. This keratinophilic mold may produce superficial disease (skin, nails) indistinguishable from dermatophytes. In Martinique, this pseudodermatophyte could represent more than 50 % of onychomycosis. Contrary to dermatophytes, the clinical response of Scytalidium spp. are typically very poor and topical treatment or systemic agents ineffective. To evaluate the potential efficacy of the new antifungal agent posaconazole, we tested in vitro 12 clinical isolates of Scytalidium spp. (seven S. dimidiatum and five S. hyalinum) against posaconazole by Etest method. For the totality of the isolates, the minimum inhibitory concentrations (MICs) were low: MICs less or equal to 0.25 microg/ml (maximum MICs of 0.25 microg/ml for S. dimidiatum and 0.032 microg/ml for S. hyalinum). These in vitro efficacy suggest that the new agent posaconazole may be a future alternative treatment.