Emergence Of Tolerance Research Articles

Impact of Environmental Sub-Inhibitory Concentrations of Antibiotics, Heavy Metals, and Biocides on the Emergence of Tolerance and Effects on the Mutant Selection Window in E. coli.

Bacteria's ability to withstand the detrimental effects of antimicrobials could occur as resistance or tolerance with the minimum inhibitory concentration, the mutant prevention concentration, and the mutant selection window as salient concepts. Thus, this study assessed the impact of exposure to extremely high doses of ampicillin on the level of persistence and tolerance development in isolates previously exposed to different concentrations of selected antibiotics, biocides, and heavy metals. These isolates were previously exposed to oxytetracycline (OXYTET), amoxicillin (AMX), copper (Cu), zinc (Zn), benzalkonium chloride (BAC) 10, dimethylammonium chloride (DADMAC) 12 and a combination of all the individual pollutants (ALL). The isolates were exposed to very high concentrations (25 × MIC) of ampicillin, and their tolerance was calculated as the time required to kill 99.9% of the bacterial population (MDK99.9). The MDK99.9 increased by 30 to 50% in test isolates (DADMAC, OXYTET, Zinc = 28 h; BAC, Copper = 30 h; amoxycillin, ALL = 26 h) compared to the untreated control. BAC-exposed isolates decreased from 2.5 × 108 CFU/mL to 2.5 × 104 CFU/mL on the second day, displaying the highest tolerance increase. The tolerance appeared to originate from two sources, i.e., stochastic persistence and genetic-induced persistence, involving multiple genes with diverse mechanisms. The mutant selection window of the isolates to ampicillin, amoxicillin, and oxytetracycline also slightly increased compared to the control, indicating the selective survival of persister cells during the 30-day exposure. These findings indicate that bacterial exposure to sub-inhibitory concentrations of environmental chemical stressors may not always result in the development of antimicrobial resistance but could initiate this process by selecting persisters that could evolve into resistant isolates.

Time-dependent effect of desensitization with wasp venom on selected parameters of the immune system

The emergence of tolerance during Hymenoptera venom immunotherapy (VIT) is a complex process. The main goal of VIT is to induce a change from proinflammatory Th2 response to the Th1 response. However, the immune mechanism of acquiring rapid tolerance during VIT has not yet been fully understood. Therefore, we have analyzed (in 4-time points: 0, 2, 6, and 24 weeks after the initiation phase of VIT) the concentration of complement C3, C4, and C5 components, lymphocyte subpopulations (flow cytometry), as well as histamine and tryptase serum concentrations of 43 patients with wasp venom allergy (III and IV Müller grade) classified to ultra-rush treatment and 18 volunteers as the control group (CG). We observed that VIT affected the immune system by inducing changes in the complement system (decreased C3 and C4 compartment protein concentrations) and "normalized" the percentage of lymphocytes and neutrophils in the peripheral blood. Moreover, a significant increase in the percentage of nTreg in the blood of patients treated with VIT was observed. On the other hand, there were no changes in histamine or tryptase concentrations in the blood. Increased percentage of nTreg cells is a well-known mechanism by which VIT affects the immune system. Finally, VIT also modulated the concentrations of the complement components, which may be a previously unknown VIT mechanism of action.

Antibiotics, Acid and Heat Tolerance of Honey adapted Escherichia coli, Salmonella Typhi and Klebsiella pneumoniae.

The medicinal importance of honey has been known for many decades due to its antimicrobial properties against life-threatening bacteria. However, previous studies revealed that microorganisms are able to develop adaptations after continuous exposure to antimicrobial compounds. The present study was conducted to explore the impact of subinhibitory concentrations of branded honey (Marhaba) and unbranded honey (extracted from Ziziphus mauritiana plant) locally available in Pakistan on Escherichia coli ATCC 10536, Salmonella Typhi and Klebsiella pneumoniae by investigating the development of self- or cross-resistance to antibiotics (gentamicin, kanamycin and imipenem). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of autoclaved honeys were determined. The bacterial cells of E. coli ATCC 10536, S. Typhi and K. pneumoniae were subjected to honey adaptation by exposing to ¼ × MIC (4 passages) and ½ × MIC (4 passages) of both honeys. Moreover, tolerance to low pH and high temperature was also studied in adapted and unadapted cells. The decreasing trend in growth pattern (OD600nm) of E. coli ATCC 10536, S. Typhi and K. pneumoniae was observed with increases in the concentration of honeys (6.25–50% v/v) respectively. Our results showed that continuous exposure of both honeys did not lead to the development of any self- or cross-resistance in tested bacteria. However, percent survival to low pH was found to be significantly higher in adapted cells as compared to unadapted cells. The results indicate that both branded honey (Marhaba) and unbranded honey (extracted from Ziziphus mauritiana plant) were effective in controlling the growth of tested pathogenic bacteria. However, the emergence of tolerance to adverse conditions (pH 2.5, temperature 60 °C) deserves further investigation before proposing honey as a better antibacterial agent in food fabrication/processing, where low pH and high temperatures are usually implemented.

Benzalkonium Chlorides: Uses, Regulatory Status, and Microbial Resistance.

Benzalkonium chlorides (BACs) are chemicals with widespread applications due to their broad-spectrum antimicrobial properties against bacteria, fungi, and viruses. This review provides an overview of the market for BACs, as well as regulatory measures and available data on safety, toxicity, and environmental contamination. We focus on the effect of frequent exposure of microbial communities to BACs and the potential for cross-resistant phenotypes to emerge. Toward this goal, we review BAC concentrations in consumer products, their correlation with the emergence of tolerance in microbial populations, and the associated risk potential. Our analysis suggests that the ubiquitous and frequent use of BACs in commercial products can generate selective environments that favor microbial phenotypes potentially cross-resistant to a variety of compounds. An analysis of benefits versus risks should be the guidepost for regulatory actions regarding compounds such as BACs.

Larvicidal Activity of Essential Oil Constituents against Malaria Vector, Anopheles gambiae (Diptera: Culicidae)

Malaria is one of the most important public health problems worldwide. This illness is controlled, mainly, by combating the vector mosquitoes using chemical insecticides, but this use has caused environmental impact and the emergence of tolerance in adult mosquitoes. Herein, we report the larvicidal activity of nine chemical constituents found in essential oils against third-instar larvae of Anopheles gambiae. All the tested compounds showed larval toxicity. Among the nine effective components, citronellol exhibited a pronounced larvicidal effect against the larvae of An. gambiae, with LC₅₀ values of 96.1 and 55.6 ppm after 12 and 24 hours of treatment, respectively; however, hydroxycitronellal was the most potent compound after 48 and 72 h of exposure (LC₅₀=3.7 and 2.3 ppm, respectively), followed by citronellol (LCso= 16.7 and 6.3 ppm, respectively). Moreover, larval mortality was concentration- and time-dependent.

Stem cell transplantation as a dynamical system: are clinical outcomes deterministic?

Outcomes in stem cell transplantation (SCT) are modeled using probability theory. However, the clinical course following SCT appears to demonstrate many characteristics of dynamical systems, especially when outcomes are considered in the context of immune reconstitution. Dynamical systems tend to evolve over time according to mathematically determined rules. Characteristically, the future states of the system are predicated on the states preceding them, and there is sensitivity to initial conditions. In SCT, the interaction between donor T cells and the recipient may be considered as such a system in which, graft source, conditioning, and early immunosuppression profoundly influence immune reconstitution over time. This eventually determines clinical outcomes, either the emergence of tolerance or the development of graft versus host disease. In this paper, parallels between SCT and dynamical systems are explored and a conceptual framework for developing mathematical models to understand disparate transplant outcomes is proposed.

“Can It Be that a Sole Authority Remains?” Epistemological Conundrums in Post-Reformation Polemic

The texts of the ancient skeptics resurfaced in the sixteenth century. How the Reformation and the subsequent confessionalization process interacted with the revival of skepticism remains disputed. Some historians contend that skeptical methods, especially those of Sextus Empiricus, were co-opted by French Catholic polemicists in the service of “counter-reformation”; others suggest that they were suppressed on both sides of the confessional divide by the new church-state establishments that were anxious to protect certainty and impose unity. Where these scholars agree, however, is on the historical trajectory of skeptical techniques: the loss of certainty in theology and the emergence of tolerance. The disputations on sacred scripture of Roberto Bellarmino and William Whitaker, the pre-eminent controversialists of late-sixteenth-century Roman Catholicism and English Calvinism, respectively, reveal the perdurance of skeptical techniques through the Reformation. They also reveal their unstable functionality. Bellarmino proposed papal supremacy as a solution to the insufficiency of reason. Whitaker then challenged the traditional foundations of ecclesiastical authority while simultaneously advancing a principle of scriptural hermeneutics that depended upon institutionally-codified dogmatic statements. Both polemicists engaged in epistemological warfare without surrendering their own claims to certainty; both established stricter ways for their churches to achieve that certainty; neither sought to promote tolerance.

Experimental limb transplantation, part ii: excellent return of function and indefinite survival after withdrawal of immunosuppression

In this study the three components of an immunosuppressive combination therapy were gradually withdrawn in a rat limb transplantation model to evaluate the effects on long-term survival of the grafted limbs, rejection rate, and functional recovery. The procedure was performed in 16 rats across a strong Brown Norway to Fischer 344 histocompatibility barrier. Eight animals served as a control group that was not given any antirejection therapy and rejected their limb within a few days. The remaining eight animals were administered a 2-week course of immunosuppressive therapy including tacrolimus (TRL; 2 mg/kg/d), mycophenolate mofetil (MMF; 15 mg/kg/d), and prednisolone (Pred; 0.5 mg/kg/d). At 2 weeks, Pred and MMF were simultaneously tapered by 20% of the dosage every week; by week 7 the animals were on TRL only. TRL was then tapered at the same rate (20% every week) to a maintenance dose of 0.6 mg/kg/d at week 12. After 6 months the immunosuppression was stopped. Four of 8 animals did not reject throughout the study up, to the 1-year endpoint. At this stage they show excellent functional outcomes, evaluated by clinical tests and walking tract analysis. The remaining four rats developed a rejection at an average of 267 days postoperatively (range 224 to 302 days), corresponding to an average of 87 days (range 44 to 122 days) without any immunosuppression. They were sacrificed as soon as rejection was confirmed for histological examination of the various tissues. This study showed that a triple combination therapy provides excellent long-term functional outcomes of the transplanted limbs, with no rejection episodes, no side effects, or complications, even 6 months after withdrawal of all immunosuppressive components, suggesting the possible emergence of tolerance.

Immune pathophysiology of aplastic anemia.

Aplastic anemia (AA) remains an elusive disease. Its pathophysiology is not only fascinating by the seemingly simple findings of cytopenia and marrow hypoplasia, but may also contain key information to the understanding of other fundamental processes such as stem cell regeneration, evolution, and immune control of clonal diseases. Although measurements of blood counts provide an objective tool to assess the disease activity and response to the therapy, immune pathophysiology of AA, as inferred from the successes of immunosuppression, provides only few other clinical clues. Similarly, the current laboratory evidence remains mostly indirect. In spite of the recognition of immune pathways of hematopoietic inhibition and apoptosis in AA, the fundamental question about the nature of the antigen(s) inciting or maintaining the pathologic immune response that ultimately leads to bone marrow failure, remains open. However, recognition of the immune targets may aid in understanding not only the pathogenesis but also many of clinical associations and the late squelae of AA. For example, abnormal cells in AA and myelodysplastic syndrome (MDS) MDS may harbor inciting antigens but the immune response lacks selectivity. Clonal selection pressure may be a result of this process or alternatively, emergence of tolerance could lead to the establishment of abnormal hematopoiesis. Clonal proliferation of large granular lymphocytosis could represent an example of an exaggerated response to an immunodominant hematopoietic antigen. In addition to the traditional functional or phenotypic analysis, pathologic immune response in AA can be studied on molecular level by identifying and quantitating T cell clones based on the presence of unique variable B-chain CDR3 sequences. Detection of clonal expansion is based on the observation that in infections and autoimmune conditions, the presence of antigenic drive will lead to the expansion and overrepresentation of T cell clones recognizing this antigen. However, simple analysis of clonal representation is not sufficient to resolve the complex nature of the immune repertoire in the context of genetic and clinical heterogeneity. Therefore, we analyzed VB and CDR3 repertoire in CD4 and CD8 cells, activated or effector cell subsets. To distinguish truly expanded and likely immunodominant clones, we first studied VB distribution and cloned CDR3 sequences from expanded VB families. Identified clonotypic sequences can be used to design molecular tests to quantitate the strength of pathologic immune response. Clonotype sharing has been confirmed in patients with similar clinical features indicating presence of common antigens. In addition, quantitative analysis showed correlation with the therapy response. Persistence and patterns of clonotypes may be helpful in the classification of immune-mediated marrow failure based on the immune characteristics and will allow inferences into the inciting pathways.

The emergence of tolerance in the Dutch Republic. Edited by C. Berkvens-Stevelinck, J. Israel and G. H. M. Posthumus Meyjes. (Studies in the History of Christian Thought, 76.) Pp. vii+280. Leiden–New York–Cologne: Brill, 1997. Nlg 173. 90 04 10768 1; 0081 8607

The emergence of tolerance in the Dutch Republic. Edited by C. Berkvens-Stevelinck, J. Israel and G. H. M. Posthumus Meyjes. (Studies in the History of Christian Thought, 76.) Pp. vii+280. Leiden–New York–Cologne: Brill, 1997. Nlg 173. 90 04 10768 1; 0081 8607 - Volume 52 Issue 2

:The Emergence of Tolerance in the Dutch Republic

Elisabeth Labrousse: Adresse du Colloque. Jonathan Israel: The Intellectual Debate about Toleration in the Dutch Republic. M.E.H.N. Mout: A Comparative View of Dutch Toleration in the Sixteenth and Early Seventeenth Centuries. James D. Tracy: Erasmus, Coornhert and the Acceptance of Religious Disunity in the Body Politic - a Low Countries Tradition? Hans Posthumus Meyjes: Tolerance et Irenisme. Hans R. Guggisberg: Castellio - Problems of Writing a New Biography. Catherine Secretan: La tolerance entre politique et rhetorique. Rob van de Schoor: The Reception of Cassander in the Republic in the Seventeenth Century. Peter G. Bietenholz: Daniel Zwicher's Views on Religious Peace and Unity. Christiane Berkvens-Stevelinck: La reception de l'Historie der Reformatie de Gerard Brandt et son influence sur la conception de la tolerance hollandaise. Hans Bots and Rob van de Schoor: La tolerance a travers les dictionnaires dans les decennies autour de 1700. Michael Heyd: The Limits of Toleration in the Early 18th Century - Shaftesbury's Letter Concerning Enthusiasm and the Reaction to it. Mario Turchetti: Elie Saurin [1639-1703] et ses Reflexions sur les droits de la Conscience. H.H.M. van Lieshout: Les querelles lexicales sur la lice de la tolerance - Pierre Jurieu attaque dans le Dictionaire Historique et Critique de Pierre Bayle. Willem Frijhoff: Dimensions de la coexistence confessionnelle. Antony McKenna: Note sur la tolerance dans la litterature philosophique clandestine de l'Age Classique. Myriam Yardeni: La tolerance retrospective - la perception de l'histoire des Pays Bas et de l'Angleterre dans le refuge huguenot.

Kinetics of the delivery of glyceryl trinitrate and isosorbide dinitrate from the transdermal systems nitropercuten and sorbopercuten in experimentsin vitro

Transdermal therapeutic systems (TTS) are dosage forms which enable the release of active substances to be controlled for extended (from days to weeks) and continuous transdermal administration of a drug into the systemic circulation at a given rate and according to a given kinetic program [1-4]. The application of TTS enables the drug concentration to be stabilized in the blood of patients at a given stationary therapeutic level (as a rule close to the minimum effective)during the whole time of applying the TTS (i.e., with opportune changing of the TTS this time can be indef'mitely long). A TTS enables the metabolism of the bulk of the drug on first pass through the liver to be avoided, and the drug action to be interrupted at any moment by simply removing the TTS from the skin surface. The usefulness of TTS has been demonstrated in the treatment and prophylaxis of serious chronic, particularly cardiovascular, illnesses, since they enable the partial uptake of drugs to be avoided, the possibility of overdosing to be avoided, and the overall quantity of drug passing into the organism to be reduced significantly due to the absence of peak concentrations in plasma, which thereby leads to a significant attenuation of drug side effects. At the present time the TTEs which have been developed abroad and used clinically include glyceryl trinitrate (GTN)Nitroderm, Nitro-Dur, Nitrosic, and Deponit [5-9], isosorbide dinitrate (ISDN) Frandol Tape [10], clonidlne Catapres [11], scopolamine Scopoderm [12], estradiol Estraderm [13], and nicotine Nicotinell, Nicoderm [14, 15], etc. We have developed a family of matrix TTS with various drugs based on an original hydrophilic matrix (Percuten) of which the TTS containing propranolol, Propercuten, has been described by us previously [16]. Data are given in the present work on two other TTS of the same family containing nitrates, viz., Nitropercuten and Sorbotpercuten (the names denote "GNT and ISDN delivered through the skin," respectively). The duration of their action is 1 day since the continuous administration of nitrates for longer may lead to the emergence of tolerance and a short pause is necessary after administering nitrates for a day. The main problem to be solved when developing a TTS with selected drugs is the provision of a rate of transdermal drug supply necessary for therapy. This depends on many factors, particularly on the composition of the polymeric diffusion matrix containing the drug which is the main constructional element of the TTS [1-4], and on the properties of the drug itself. The first stage in the development of a TTS is usually a study of the kinetics of drug supply from the TTS in vitro through a membrane with properties unchanged during the experiment.* Under standard conditions the diffusion characteristics of skin vary and depend on the actual patient and the place of application of the system. The interpretation of data obtained in vivo is therefore more complex than that of data obtained in vitro. We showed previously [ 16] that the matrix TTS containing propranolol, viz., Propercuten, which is related in composition to Nitropercuten and Sorbopercuten, is characterized in experiments in vitro by a high rate of supply of propranolol, constant with time up to the release of 84% of the total drug contained in the matrix. The kinetics of the supply of drug from the diffusion matrix of the TTS through the epidermis of the skin of a human corpse, or a Carbosil polymeric membrane modeling it in in vitro experiments, were described by Fick's first law of diffusion in the following form:

Temperature responses in rats after acute and chronic administrations of caffeine

Acute administrations (IP) of caffeine produced dose-dependent changes in the body temperature of rats. Low doses (12.5 and 25 mg/kg) induced hyperthermia soon after drug administration, while high doses (50 and 100 mg/kg) produced maximal hypothermia approximately 2 hr later. The acute effects of caffeine were also dependent on ambient temperature. The hyperthermic and hypothermic responses were attenuated and blocked, respectively, in rats maintained at 32 degrees C. At 4 degrees C, the hypothermic response was exacerbated, and the hyperthermic response was absent. Tolerance rapidly developed to the hypothermic actions of caffeine when rats were administered the drug over 28 days. Following the emergence of tolerance, hyperthermia was observed in rats given 50 mg/kg of caffeine. The hyperthermic responses to the low doses of caffeine were not altered by the frequency of drug administration. Both the acute and chronic effects of caffeine on thermoregulation are not unlike those found for morphine. Possible mechanisms of action underlying the thermoregulatory effects of caffeine are discussed.