Dose-response Kinetics Research Articles

Comparison of the Antimicrobial Efficacy and Germicidal Efficiency of 405-nm Light for Surface Decontamination

Background The persistence of infectious organisms on hospital surfaces presents a significant challenge to healthcare environments. Low irradiance visible 405-nm light has recently been developed as a method for environmental decontamination, with studies demonstrating successful reductions of environmental bacteria in wards and operating theatres. This study investigates the antimicrobial efficacy of 405-nm light for decontamination of surfaces, and how the dose-response kinetics are affected by use of differing light irradiances. Methods Surface-seeded Staphylococcus aureus and Pseudomonas aeruginosa (selected as model Gram-positive and Gram-negative species) were exposed to increasing doses of 405-nm light (≤ 90 Jcm-2) at three discrete irradiances (0.5, 5 and 50 mWcm-2). For both species, inactivation kinetics at each respective irradiance was established and susceptibility at equivalent light doses compared. Results Results demonstrate increased bacterial susceptibility to 405-nm light inactivation when exposed at lower irradiance treatments. For both species, 3 Jcm-2 was required when exposed using 0.5 mWcm-2 irradiance to achieve significant bacterial inactivation (P < 0.05; 26.7-73.7% reduction). When exposed at 5 mWcm-2, double the energy (6 Jcm-2) was required to achieve similar reductions. Exposure at the highest irradiance (50 mWcm-2) required 3-5 times greater dose (9-15 Jcm-2) to achieve similar reductions to the lowest irradiance tested (0.5 mWcm-2). Conclusion This study provides evidence of the enhanced germicidal efficiency of low irradiance 405-nm light, highlighting its efficacy for continuous environmental decontamination applications. Further investigation into the photo-chemical inactivation mechanisms will be crucial for its optimisation for a range of infection control applications.

Bmim]FeCl4 mediated inhibition and toxicity during anaerobic digestion: Dose-response kinetics, biochar-dependent detoxification and microbial resistance

[Bmim]FeCl4, or 1‑butyl‑3-methylimidazolium tetrachloroferrate, is a typical ionic liquid (IL). Its recyclable, magnetic, multicomponent, and solvent-free nature makes it a particularly attractive ionic liquid for use in industrial processes. Despite its widespread use, the potential hazards that [Bmim]FeCl4 might pose to the environment, including productive microorganisms, have not been explored. In this study, the dose-response of [Bmim]FeCl4 in anaerobic digestion (AD) was investigated to assess the potential toxification and biochar-dependent detoxification in microbial communities, including enzymatic activity and molecule docking dynamics. Our results showed that methane production (31.52 mLmax/gVS) was sharply inhibited following [Bmim]FeCl4 treatment. Moreover, increasing the dosage of [Bmim]FeCl4 caused more dissolved organic matter (DOM) to be generated. Interestingly, 0.4 g/L of [Bmim]FeCl4 could stimulate the high activity of microbial hydrolase and ATPase. However, a higher concentration of 2.65 g/L prevented these enzymatic processes from continuing. At the cellular level, higher concentration of [Bmim]FeCl4 (>0.4 g/L) increased malondialdehyde (MDA) levels, leading to a higher cell lethal rate and weakening of the secondary structures of protein (especially, the amide I region). At the molecular level, the competitive H-bonding in the active sites caused low activity and consummated more energy. At the community level, structural equation modeling (SEM) revealed that [Bmim]FeCl4 and biochar were the main drivers for microbial community succession. For instance, high [Bmim]FeCl4 (8 g/L) benefited the growth of Clostridium sensu_stricto (from ≤1% to 27%). It is worth mentioning that biochar reversed the inhibition with high α-diversity, which caused a resurgence in the activity of previously inhibited ATPase and hydrolase. H2-trophic methanogens (Methanolinea and Methaofastidisoum) were sensitive to [Bmim]FeCl4 and decreased linearly while acetoclastic methanogens (Methanosaeta) were unchanged. These findings were consistent with the short-term activity tests and further verified by functional analysis.

Increased removal of cadmium by Chlamydomonas reinhardtii modified with a synthetic gene for γ-glutamylcysteine synthetase

Bioremediation with genetically modified microalgae is becoming an alternative to remove metalloids and metals such as cadmium, a contaminant produced in industrial processes and found in domestic waste. Its removal is important in several countries including Mexico, where the San Luis Potosi region has elevated levels of it. We generated a construct with a synthetic gene for γ-glutamylcysteine synthetase and employed it in the chloroplast transformation of Chlamydomonas reinhardtii. In dose-response kinetics with media containing from 1 to 20 mg/L of cadmium, both the transplastomic clone and the wild-type strain grew similarly, but the former removed up to 32% more cadmium. While the growth of both decreased with higher concentrations of cadmium, the transplastomic clone removed 20 ± 9% more than the wild-type strain. Compared to the wild-type strain, in the transplastomic clone the activity of glutathione S-transferase and the intracellular glutathione increased up to 2.1 and 1.9 times, respectively, in media with 2.5 and 10 mg/mL of cadmium. While 20 mg/L of cadmium inhibited the growth of both, the transplastomic clone gradually duplicated. These results confirm the expression of the synthetic gene gshA in the transformed strain as revealed in its increased removal uptake and metabolic response.

Global priority multidrug-resistant pathogens do not resist photodynamic therapy

Microbial drug-resistance demands immediate implementation of novel therapeutic strategies. Antimicrobial photodynamic therapy (aPDT) combines the administration of a photosensitizer (PS) compound with low-irradiance light to induce photochemical reactions that yield reactive oxygen species (ROS). Since ROS react with nearly all biomolecules, aPDT offers a powerful multitarget method to avoid selection of drug-resistant strains. In this study, we assayed photodynamic inactivation under a standardized method, combining methylene blue (MB) as PS and red light, against global priority pathogens. The species tested include Acinetobacter baumannii, Klebsiella aerogenes, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecium, Enterococcus faecalis, Staphylococcus aureus, Candida albicans and Cryptococcus neoformans. Our strain collection presents resistance to all tested antimicrobials (>50). All drug-resistant strains were compared to their drug-sensitive counterparts. Regardless of resistance phenotype, MB-aPDT presented species-specific dose-response kinetics. More than 5log10 reduction was observed within less than 75 s of illumination for A. baumannii, E. coli, E. faecium, E. faecalis and S. aureus and within less than 7 min for K. aerogenes, K. pneumoniae, P. aeruginosa, C. albicans and C. neoformans. No signs of correlations in between drug-resistance profiles and aPDT sensitivity were observed. Therefore, MB-aPDT can provide effective therapeutic protocols for a very broad spectrum of pathogens. Hence, we believe that this study represents a very important step to bring aPDT closer to implementation into mainstream medical practices.

Development of Photochemical Microsensors for Evaluating Photosynthetic Light Dose Distributions in Microalgal Photobioreactors.

We describe the development and testing of a Lagrangian method for quantifying light dose distributions within photobioreactors (PBRs) using novel photochemical microsensors. These microsensors were developed using 3-μm microspheres coated with a fluorescent dye that responds to wavelengths of visible light that are critical for photosynthesis. The dose-response kinetics of the microsensors was established by varying known doses of collimated light and quantifying the fluorescence responses of individual particles using flow cytometry. A deconvolution scheme was used to determine the light dose distribution from the fluorescence distribution of the microsensors. As proof-of-concept, the microsensors were used to quantify the photosynthetic light dose distributions within a gently mixed, 3 L flat-plate, batch PBR with and without algae and no gas bubbling and without algae but with gas bubbling. The microsensor approach not only provided information about the photosynthetic light distributions within the PBRs but also predicted the average light attenuation due to algal cells within 1% of estimates made with an in situ light sensor. The results showed that bubbles, under the conditions tested, increased the overall light irradiance by 18%; a result not captured by static measurements. The Lagrangian microsensors provide a novel approach for quantifying light within a photobioreactor.

Quantitative analysis of the dose-response of white spot syndrome virus in shrimp.

White spot syndrome virus (WSSV) is an important cause of mortality and economic losses in shrimp farming. Although WSSV-induced mortality is virus dose dependent and WSSV infection does not necessarily lead to mortality, the relationships between virus-particle dose, infection and mortality have not been analysed quantitatively. Here, we explored WSSV dose-response by a combination of experiments, modelling and meta-analysis. We performed dose-response experiments in Penaeus vannamei postlarvae, recorded host mortality and detected WSSV infection. When we fitted infection models to these data, two models-differing in whether they incorporated heterogeneous host susceptibility to the virus or not-were supported for two independent experiments. To determine the generality of these results, we reanalysed published data sets and then performed a meta-analysis. We found that WSSV dose-response kinetics is indeed variable over experiments. We could not clearly identify which specific infection model has the most support by meta-analysis, but we argue that these results also are most concordant with a model incorporating varying levels of heterogeneous host susceptibility to WSSV. We have identified suitable models for analysing WSSV dose-response, which can elucidate the most basic virus-host interactions and help to avoid underestimating WSSV infection at low virus doses.

Prospective MRI Assessment of Serial Dose-Response Kinetics of Swallowing Muscles in Oropharyngeal Cancer Patients Treated With Radiation Therapy and Correlations With Dynamic Imaging Grade for Swallowing Toxicity (DIGEST)

Prospective MRI Assessment of Serial Dose-Response Kinetics of Swallowing Muscles in Oropharyngeal Cancer Patients Treated With Radiation Therapy and Correlations With Dynamic Imaging Grade for Swallowing Toxicity (DIGEST)

OC-0334: Prospective MR assessment of dose-response kinetics of non-target muscles in head and neck cancer

OC-0334: Prospective MR assessment of dose-response kinetics of non-target muscles in head and neck cancer

Uptake of synthetic naked RNA by skin-resident dendritic cells via macropinocytosis allows antigen expression and induction of T-cell responses in mice.

Intradermal administration of antigen-encoding RNA has entered clinical testing for cancer vaccination. However, insight into the underlying mechanism of RNA uptake, translation and antigen presentation is still limited. Utilizing pharmacologically optimized naked RNA, the dose-response kinetics revealed a rise in reporter signal with increasing RNA amounts and a prolonged RNA translation of reporter protein up to 30days after intradermal injection. Dendritic cells (DCs) in the dermis were shown to engulf RNA, and the signal arising from the reporter RNA was significantly diminished after DC depletion. Macropinocytosis was relevant for intradermal RNA uptake and translation in vitro and in vivo. By combining intradermal RNA vaccination and inhibition of macropinocytosis, we show that effective priming of antigen-specific CD8(+) T-cells also relies on this uptake mechanism. This report demonstrates that direct antigen translation by dermal DCs after intradermal naked RNA vaccination is relevant for efficient priming of antigen-specific T-cells.

Investigation of DNA Damage Dose-Response Kinetics after Ionizing Radiation Schemes Similar to CT Protocols.

Although there has been extensive research done on the biological response to doses of ionizing radiation relevant to radiodiagnostic procedures, very few studies have examined radiation schemes similar to those frequently utilized in CT exams. Instead of a single exposure, CT exams are often made up of a series of scans separated on the order of minutes. DNA damage dose-response kinetics after radiation doses and schemes similar to CT protocols were established in both cultured (ESW-WT3) and whole blood lymphocytes and compared to higher dose exposures. Both the kinetics and extent of H2AX phosphorylation were found to be dose dependent. Damage induction and detection showed a clear dose response, albeit different, at all time points and differences in the DNA repair kinetics of ESW-WT3 and whole blood lymphocytes were characterized. Moreover, using a modified split-dose in vitro experiment, we show that phosphorylation of H2AX is significantly reduced after exposure to CT doses fractionated over a few minutes compared to the same total dose delivered as a single exposure. Because the split-dose exposures investigated here are more similar to those experienced during a CT examination, it is essential to understand why and how these differences occur. This work provides compelling evidence supporting differential biological responses not only between high and low doses, but also between single and multiple exposures to low doses of ionizing radiation.

Abstract 4291: A novel image-based cytometry method for autophagy detection in living cells

Abstract Autophagy is an important cellular catabolic process that plays a variety of important roles, including maintenance of the amino acid pool during starvation, recycling of damaged proteins and organelles, and clearance of intracellular microbes. Currently employed autophagy detection methods include fluorescence microscopy, biochemical measurement, SDS-PAGE, and Western blotting, but they are time-consuming, labor-intensive, and require much experience for accurate interpretation. More recently, development of novel fluorescent probes have allowed the investigation of autophagy via standard flow cytometry. However, flow cytometers remain relatively expensive and require a considerable amount of maintenance. Previously, image-based cytometry has been shown to perform automated fluorescence-based cellular analysis comparable to flow cytometry. In this study, we developed a novel method using the Cellometer image-based cytometer in combination with Cyto-ID® Green dye for autophagy detection in live cells. The method is compared to flow cytometry by measuring macroautophagy in nutrient-starved Jurkat cells. Results demonstrate similar trends of autophagic response, but different magnitude of fluorescence signal increases, which may arise from different analysis approaches characteristic of the two instrument platforms. The possibility of using this method for drug discovery applications is also demonstrated through the measurement of dose-response kinetics upon induction of autophagy with rapamycin and tamoxifen. The described image-based cytometry/fluorescent dye method should serve as a useful addition to the current arsenal of techniques available in support of autophagy-based drug discovery relating to various pathological disorders. Citation Format: Leo Li-Ying Chan, Dee Shen, Alisha R. Wilkinson, Wayne Patton, Ning Lai, Eric Chan, Dmitry Kuksin, Bo Lin, Jean Qiu. A novel image-based cytometry method for autophagy detection in living cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4291. doi:10.1158/1538-7445.AM2014-4291

Radiation-induced conformational changes in chromatin structure in resting human peripheral blood mononuclear cells

Background: Ionizing radiation induces a plethora of DNA damage including double-strand breaks (DSB) that may trigger a series of events such as transcription, DNA repair and alteration in the conformation of chromatin structure in human cells. We have made an attempt to study the conformational changes in chromatin fibers in irradiated human peripheral blood mononuclear cells (PBMC) using Dynamic Light Scattering (DLS) as a new tool.Materials and methods: Venous blood samples were collected from 10 random, healthy individuals with written informed consent, approved by institutional ethics committee. PBMC were separated from blood, irradiated with different doses of gamma radiation from 0.25–1.0 Gy. Native chromatin was isolated from irradiated PBMC and changes in the hydrodynamic diameter of the chromatin fiber were measured using DLS. Both dose response and time kinetics was studied in order to see the chromatin changes. Radiation-induced DNA double-strand breaks were measured using gamma-H2AX (histone 2A member X) as a biomarker using flow cytometry and foci were visualized in confocal microscopy.Results: A significant alteration in hydrodynamic diameter of the chromatin fiber was observed at lower doses (0.25 and 0.50 Gy), whereas at higher dose (1.0 Gy), the size of the chromatin fiber was comparable to unirradiated control. Among the 10 individuals studied, five individuals showed significant increase (p ≤ 0.002) in hydrodynamic size at 0.25 Gy whereas four individuals showed significant decrease (p ≤ 0.009) at 0.25 Gy. One individual did not show any significant difference as compared to control. However, dose-dependent increase in gamma-H2AX fluorescence signals as well as foci number was observed. Increased fragmentation of chromatin fiber was also observed using Atomic Force Microscopy at higher doses.Conclusion: Radiation-induced DNA damage response can lead to individual specific conformational changes in chromatin structure at lower doses (0.25 Gy and 0.50 Gy) which can be detected using dynamic light scattering method in resting human PBMC.

Dose response kinetics of CD8 lymphocytes from young animals transfused into old animals and challenged with influenza

Transfusion of autologous leukocytes after prolonged storage has been proposed as a means of rejuvenating the immune system of older individuals. The rationale for this approach is that age related immune decline is associated with a diminished pool of naïve T cells following atrophy of the thymus and reduction in thymic output. The presence of high levels of naïve T cells within the blood of young individuals could provide a boost to the immune system of an older “self” through a rejuvenation of the naïve T cell pool. However what remains unresolved is whether the cells could be incorporated effectively into the T cell pool of the host and whether effectors could be generated. Using CD45 congenic mice in our experiments we show that the transfusion of young donor cells into older congenic host animals leads to their successful incorporation into the peripheral T cell pool. When the recipients were challenged with influenza virus, specific effector CD8 cells were generated which were of both host and donor origin. We found no relationship between the number of responder cells of donor origin at the time of assay and the number of cells injected.

Integrating Mitochondrial Energetics, Redox and Ros Metabolic Networks: A Two-Compartment Model

To understand the mechanisms involved in the control and regulation of mitochondrial reactive oxygen species (ROS) levels, a two-compartment computational Mitochondrial Energetic-Redox (ME-R) model accounting for energetic, redox and ROS metabolisms is presented. The ME-R model incorporates four main redox couples (NADH/NAD+, NADPH/NADP+, GSH/GSSG, Trx(SH)2/TrxSS). Main scavenging systems - glutathione, thioredoxin, superoxide dismutase, catalase - are distributed in mitochondrial matrix and extra-matrix compartments, and transport between compartments of ROS species (superoxide: O2.-, hydrogen peroxide: H2O2), and GSH is also taken into account. Model simulations are compared with experimental data obtained from isolated heart mitochondria. The ME-R model is able to simulate: i) the shape and order of magnitude of H2O2 emission and dose-response kinetics observed after treatment with inhibitors of the GSH or Trx scavenging systems; and ii) steady and transient behavior of ΔΨm and NADH after single or repetitive pulses of substrate- or uncoupler-elicited energetic-redox transitions. The dynamics of the redox environment in both compartments is analyzed with the model following substrate addition. The ME-R model represents a useful computational tool for exploring ROS dynamics, the role of compartmentation in the redox environment modulation, and the role of redox regulation in the control of mitochondrial function.

Integrating Mitochondrial Energetics, Redox and ROS Metabolic Networks: A Two-Compartment Model

To understand the mechanisms involved in the control and regulation of mitochondrial reactive oxygen species (ROS) levels, a two-compartment computational mitochondrial energetic-redox (ME-R) model accounting for energetic, redox, and ROS metabolisms is presented. The ME-R model incorporates four main redox couples (NADH/NAD+, NADPH/NADP+, GSH/GSSG, Trx(SH)2/TrxSS). Scavenging systems—glutathione, thioredoxin, superoxide dismutase, catalase—are distributed in mitochondrial matrix and extra-matrix compartments, and transport between compartments of ROS species (superoxide: O2⋅−, hydrogen peroxide: H2O2), and GSH is also taken into account. Model simulations are compared with experimental data obtained from isolated heart mitochondria. The ME-R model is able to simulate: i), the shape and order of magnitude of H2O2 emission and dose-response kinetics observed after treatment with inhibitors of the GSH or Trx scavenging systems and ii), steady and transient behavior of ΔΨm and NADH after single or repetitive pulses of substrate- or uncoupler-elicited energetic-redox transitions. The dynamics of the redox environment in both compartments is analyzed with the model following substrate addition. The ME-R model represents a useful computational tool for exploring ROS dynamics, the role of compartmentation in the modulation of the redox environment, and how redox regulation participates in the control of mitochondrial function.

A novel image-based cytometry method for autophagy detection in living cells

Autophagy is an important cellular catabolic process that plays a variety of important roles, including maintenance of the amino acid pool during starvation, recycling of damaged proteins and organelles, and clearance of intracellular microbes. Currently employed autophagy detection methods include fluorescence microscopy, biochemical measurement, SDS-PAGE and western blotting, but they are time consuming, labor intensive, and require much experience for accurate interpretation. More recently, development of novel fluorescent probes have allowed the investigation of autophagy via standard flow cytometry. However, flow cytometers remain relatively expensive and require a considerable amount of maintenance. Previously, image-based cytometry has been shown to perform automated fluorescence-based cellular analysis comparable to flow cytometry. In this study, we developed a novel method using the Cellometer image-based cytometer in combination with Cyto-ID® Green dye for autophagy detection in live cells. The method is compared with flow cytometry by measuring macroautophagy in nutrient-starved Jurkat cells. Results demonstrate similar trends of autophagic response, but different magnitude of fluorescence signal increases, which may arise from different analysis approaches characteristic of the two instrument platforms. The possibility of using this method for drug discovery applications is also demonstrated through the measurement of dose-response kinetics upon induction of autophagy with rapamycin and tamoxifen. The described image-based cytometry/fluorescent dye method should serve as a useful addition to the current arsenal of techniques available in support of autophagy-based drug discovery relating to various pathological disorders.

Gamma-H2AX foci in cells exposed to a mixed beam of X-rays and alpha particles

BackgroundLittle is known about the cellular effects of exposure to mixed beams of high and low linear energy transfer radiation. So far, the effects of combined exposures have mainly been assessed with clonogenic survival or cytogenetic methods, and the results are contradictory. The gamma-H2AX assay has up to now not been applied in this context, and it is a promising tool for investigating the early cellular response to mixed beam irradiation.PurposeTo determine the dose response and repair kinetics of gamma-H2AX ionizing radiation-induced foci in VH10 human fibroblasts exposed to mixed beams of 241Am alpha particles and X-rays.ResultsVH10 human fibroblasts were irradiated with each radiation type individually or both in combination at 37°C. Foci were scored for repair kinetics 0.5, 1, 3 and 24 h after irradiation (one dose per irradiation type), and for dose response at the 1 h time point. The dose response effect of mixed beam was additive, and the relative biological effectiveness for alpha particles (as compared to X-rays) was of 0.76 ± 0.52 for the total number of foci, and 2.54 ± 1.11 for large foci. The repair kinetics for total number of foci in cells exposed to mixed beam irradiation was intermediate to that of cells exposed to alpha particles and X-rays. However, for mixed beam-irradiated cells the frequency and area of large foci were initially lower than predicted and increased during the first 3 hours of repair (while the predicted number and area did not).ConclusionsThe repair kinetics of large foci after mixed beam exposure was significantly different from predicted based on the effect of the single dose components. The formation of large foci was delayed and they did not reach their maximum area until 1 h after irradiation. We hypothesize that the presence of low X-ray-induced damage engages the DNA repair machinery leading to a delayed DNA damage response to the more complex DNA damage induced by alpha particles.

Simultaneous measurement of benzo[a]pyrene‐induced Pig‐a and lacZ mutations, micronuclei and dna adducts in mutaTMmouse

In this study we compared the response of the Pig-a gene mutation assay to that of the lacZ transgenic rodent mutation assay, and demonstrated that multiple endpoints can be measured in a 28-day repeat dose study. Muta™Mouse were dosed daily for 28 days with benzo[a]pyrene (BaP; 0, 25, 50 and 75 mg/kg body weight/day) by oral gavage. Micronucleus (MN) frequency was determined in reticulocytes (RETs) 48 hr following the last dose. 72 h following the last dose, mice were euthanized, and tissues (glandular stomach, small intestine, bone marrow and liver) were collected for lacZ mutation and DNA adduct analysis, and blood was evaluated for Pig-a mutants. BaP-derived DNA adducts were detected in all tissues examined and significant dose-dependent increases in mutant Pig-a phenotypes (i.e., RETCD24- and RBC CD24-) and lacZ mutants were observed. We estimate that mutagenic efficiency (i.e., rate of conversion of adducts into mutations) was much lower for Pig-a compared to lacZ, and speculate that this difference is likely explained by differences in repair capacity between the gene targets, and differences in the cell populations sampled for Pig-a versus lacZ. The BaP doubling doses for both gene targets, however, were comparable, suggesting that similar mechanisms are involved in the accumulation of gene mutations. Significant dose-related increases in % MN were also observed; however, the doubling dose was considerably higher for this endpoint. The similarity in dose response kinetics of Pig-a and lacZ provides further evidence for the mutational origin of glycosylphosphatidylinositol (GPI)-anchor deficiencies detected in the Pig-a assay. Environ. Mol. Mutagen. 2011. © 2011 Wiley-Liss, Inc.

Evaluation of toxic effects of several carboxylic acids on bacterial growth by toxicodynamic modelling

BackgroundEffects of organic acids on microbial fermentation are commonly tested in investigations about metabolic behaviour of bacteria. However, they typically provide only descriptive information without modelling the influence of acid concentrations on bacterial kinetics.ResultsWe developed and applied a mathematical model (secondary model) to capture the toxicological effects of those chemicals on kinetic parameters that define the growth of bacteria in batch cultures. Thus, dose-response kinetics were performed with different bacteria (Leuconostoc mesenteroides, Carnobacterium pisicola, Escherichia coli, Bacillus subtilis and Listonella anguillarum) exposed at increasing concentrations of individual carboxylic acids (formic, acetic, propionic, butyric and lactic). In all bioassays the acids affected the maximum bacterial load (Xm) and the maximum growth rate (vm) but only in specific cases the lag phase (λ) was modified. Significance of the parameters was always high and in all fermentations the toxicodynamic equation was statistically consistent and had good predictability. The differences between D and L-lactic acid effects were significant for the growth of E. coli, L. mesenteroides and C. piscicola. In addition, a global parameter (EC50,τ) was used to compare toxic effects and provided a realistic characterization of antimicrobial agents using a single value.ConclusionsThe effect of several organic acids on the growth of different bacteria was accurately studied and perfectly characterized by a bivariate equation which combines the basis of dose-response theory with microbial growth kinetics (secondary model). The toxicity of carboxylic acids was lower with the increase of the molecular weight of these chemicals.

Dose response and repair kinetics of γ-H2AX foci induced by in vitro irradiation of whole blood and T-lymphocytes with X- and γ-radiation

Purpose: Dose response and repair kinetics of phosphorylated histone H2A isoform X (γ-H2AX) foci in T-lymphocytes were investigated in the low-dose range after in vitro irradiation of whole blood and T-lymphocytes with 100 kVp X-rays and 60Co γ-rays.Materials and methods: Whole blood or isolated T-lymphocytes were irradiated in vitro and γ-H2AX foci were scored. Dose response was determined in the 0–500 mGy dose range. Foci kinetics were studied at doses of 5 and 200 mGy up to 24 h post-irradiation.Results: After X-irradiation, the dose response for whole blood shows a biphasic behaviour with a low-dose hypersensitivity, which is less pronounced for isolated T-lymphocytes. In contrast, γ-radiation shows a linear dose response for both irradiation conditions. Concerning repair kinetics, delayed repair was found after X-ray whole blood irradiation (5 and 200 mGy) with 40% of the foci persisting 24 h post-irradiation. This number of foci is reduced to 10% after irradiation of isolated T-lymphocytes with 200 mGy X-rays. On the contrary, γ-H2AX foci are reduced to background levels 24 h post-irradiation with 200 mGy 60Co γ-rays.Conclusion: γ-H2AX foci response and repair kinetics depend on irradiation conditions and radiation quality, possibly linked to Bystander response.