Surveillance uncovers the smoking gun for resistance emergence

Today, antibiotic resistance is becoming a major healthcare concern. As global travel increases, more antibiotic-resistant bacteria will be disseminated from one country to another, thereby imposing a problem worldwide. Since the development of resistance is an evolutionary process, constant surveillance is needed to gain insight into the problem and surveillance studies needed to document the spread of antibiotic resistance. The basic objectives of surveillance studies in antimicrobial resistance are: to determine the level of resistance in a particular geographical area; to monitor changes in the level of resistance and make this information available to therapeutic policy-makers, as well as to detect new mechanisms of resistance for use as early warning signs; to study how such resistance develops, persists and spreads, and to monitor interventions. Although, surveillance provides the smoking gun for emergence of antibiotic resistance, improvement of the system is necessary and may be achieved through enhanced information technology and diagnostic tools.     

Multidrug resistance phenotype associated with selection of an aminopterin resistant dog kidney cell line.

A determination of the mechanisms of drug resistance in tumour cells is important for developing strategies to combat such resistance in persons receiving chemotherapy. This report describes a combined cellular, biochemical, and molecular analysis of a dog kidney cell line selected for resistance to increasing levels of the hydrophilic antifolate, aminopterin. Three distinct drug resistance phenotypes were observed in cells exhibiting high levels of aminopterin resistance. Two of these phenotypes were decreased aminopterin accumulation and increased levels of dihydrofolate reductase specific activity. The third drug resistance phenotype was noted initially as cross resistance to a variety of hydrophobic drugs indicating multidrug resistance. Biochemical assays demonstrated reduced accumulation of the hydrophobic fluorescent drug daunorubicin and of 3H-colchicine in the aminopterin resistant cells. These results were then correlated with increased levels of the multidrug resistance (mdr) gene product, P-glycoprotein, and mdr mRNA levels in the aminopterin resistant cells. However, experiments designed to prove a role for expression of the mdr gene in providing a degree of aminopterin resistance were unsuccessful. It is concluded that aminopterin selection in these dog kidney cells resulted in expression of at least three distinct drug resistance phenotypes and that one of these phenotypes, multidrug resistance, represented a secondary response to the aminopterin selection.     

Determination of the real standard distribution of susceptible strains in zone histograms

The procedure for NRI, a method for normalised resistance interpretation, is presented. By means of its promising autocalibration system the method generates zone breakpoints for resistance in zone diameter histograms for bacterial species-antibiotic combinations. These breakpoints give a normalised interpretation of resistance which is independent of disc test standard chosen, disc potency, medium used, inoculum size, etc. of the individual laboratory as long as the performance shows good reproducibility and precision. The method should be further tested as a tool for setting "bacteriological breakpoints" or "epidemiological breakpoints", for calculating resistance rates for comparative purposes, e.g. in antibiotic resistance surveillance, and for quality control of the disc diffusion test.     

血管生成抑制剂的耐药机制研究进展

血管生成是实体肿瘤发展、转移的关键步骤。近年来,血管生成抑制剂已应用于临床,并成为控制肿瘤的一个重要策略。鉴于许多患者在开始接受血管抑制剂治疗时或治疗数月后出现耐药现象,探索耐药机制已成为解决耐药问题、提高化疗效果的关键。     

Insulin resistance and antidiabetic drugs.

Insulin resistance describes an impaired biological response to insulin, which underpins the development of type 2 (non-insulin-dependent) diabetes mellitus (T2DM). Initially, insulin resistance causes a compensatory hyperinsulinaemia, which gives way to pancreatic beta-cell failure. Insulin resistance and hyperinsulinaemia conspire together in the development of a diverse collection of risk factors for coronary heart disease, namely obesity, T2DM, dyslipidaemia, hypertension, atherosclerosis, and a pro-coagulant state. This collection of factors is commonly found in T2DM patients, and is recognised as the Insulin Resistance Syndrome or Syndrome X. By targeting insulin resistance as a treatment strategy for T2DM, it should be possible to broaden the potential benefits, so that improved glycaemic control is complemented with improvements to other components of Syndrome X. At present, metformin and thiazolidinediones are the only therapies for T2DM that directly address aspects of insulin resistance. Increasing awareness of the clinical implications of insulin resistance, and increasing knowledge of the cellular basis of insulin resistance, provide the rationale and a means for developing an anti-insulin resistance approach to the treatment of T2DM.     

Resistance to cytotoxic and anti-angiogenic anticancer agents: similarities and differences.

Intrinsic resistance to anticancer drugs, or resistance developed during chemotherapy, remains a major obstacle to successful treatment. This is the case both for resistance to cytotoxic agents, directed at malignant cells, and for resistance to anti-angiogenic agents, directed at non-malignant endothelial cells. In this review, we will discuss mechanisms of resistance which have a bearing on both these conceptually different classes of drugs. The complexity of drug resistance, involving drug transporters, such as P-glycoprotein, as well as resistance related to the tissue structure of solid tumors and its consequences for drug delivery is discussed. Possible mechanisms of resistance to endothelial cell-targeted drugs, including inhibitors of the VEGF receptor and EGF receptor family, are reviewed. The resistance of cancer cells as well as endothelial cells related to anti-apoptotic signaling events initiated by cell integrin-matrix interactions is discussed. Current strategies to overcome resistance mechanisms are summarized; they include high-dose chemotherapy, tumor targeting of cytotoxics to improve tumor uptake, low-dose protracted (metronomic) chemotherapy and combinations of classical agents with anti-angiogenic agents. This review discusses primarily literature published in 2001 and 2002.     

Antiplatelet drug resistance: not ready for prime time

Antiplatelet drug therapy reduces vascular events in a wide range of patients. Although antiplatelet drug resistance is becoming well documented, a universal definition has not been established. This lack and the lack of standardized measures of platelet function make estimation of the prevalence of antiplatelet drug resistance difficult. Mounting evidence suggests that antiplatelet drug resistance is associated with adverse clinical outcomes, which have been assessed in patients with coronary artery disease, myocardial infarction, cerebrovascular disease, and peripheral vascular disease. Patients with antiplatelet drug resistance have significantly more vascular events than patients without such resistance. However, there are no guidelines for the treatment of antiplatelet drug resistance. Although point-of-care platelet-function testing makes screening for resistance feasible, routine screening should not be standard practice until data regarding the management of antiplatelet drug resistance are available.     

Resistance in wheat to Fusarium infection and trichothecene formation

The state of the art in Fusarium head blight resistance research is reviewed with reference to breeding for genetic resistance to Fusarium in wheat in practice. Fusarium graminearum and F. culmorum produce the trichothecene mycotoxin deoxynivalenol (DON). DON has phytotoxic properties and is an important aggressiveness factor in head blight. Head blight resistance in wheat is not specific for either F. graminearum or F. culmorum. Resistance components include resistance to penetration, resistance to colonization and mechanisms that influence kernel DON content. The resistance to Fusarium in wheat is a quantitative trait with relative high heritability and controlled by a few genes with major effect. A major quantitative trait locus (QTL) for head blight resistance from the Chinese variety Sumai 3 has been identified and verified by several research groups via molecular marker analysis. Research is now directed at identifying additional QTLs to make accumulation of resistance genes in elite wheat lines possible. The policy of official variety list trials may affect the head blight resistant level of future wheat varieties by excluding candidate varieties that are a too susceptible to Fusarium. A higher level of Fusarium head blight will guarantee lower risks for the farmer of crop loss due to reduced grain yield, low quality and mycotoxin contamination.     

Supranational surveillance of antimicrobial resistance: The legacy of the last decade and proposals for the future

Antimicrobial resistance among clinically important bacteria is widely acknowledged as a major global public health threat. A decade ago, several supranational surveillance initiatives were introduced. Few of them are still ongoing, and only one features an interactive database in the public domain. No public surveillance system monitors resistance trends among non-invasive isolates on a supranational level. Although the relevance of measuring antimicrobial resistance in invasive isolates is undisputable and there is a large consensus on sampling techniques for these isolates, surveillance systems monitoring invasive infections will only have low sensitivity for early detection of emerging resistance trends, also missing an important opportunity for intervention. Surveillance of resistance patterns should ideally include characterization of important clones involved in the dissemination of resistance. This review also emphasizes important methodological issues to be considered whenever performing surveillance, and provides general recommendations applicable to surveillance at all levels.     

Pathobiology of Lomentospora prolificans: could this species serve as a model of primary antifungal resistance?

The number of fungal isolates resistant to antifungal drugs has increased dramatically over the last few years and has become an important concern for clinicians. Among these isolates, fungi showing multidrug resistance are particularly worrying because of the difficulties associated with their treatment. These factors hamper the successful recovery of patients and drastically raise mortality rates. Antifungal resistance is multifactorial and several mechanisms in different fungi have been described. There is a need to study these mechanisms in depth; however, the study of antifungal drug resistance separately for each individual species makes progress in the field very slow and tedious. The selection of a multiresistant microorganism as a model for understanding resistance mechanisms and extrapolating the results to other species could help in the search for a solution. In this mini-review, we describe the pathobiology of Lomentospora (Scedosporium) prolificans, paying special attention to its intrinsic resistance to all currently available antifungal agents. The characteristics of L. prolificans offer several advantages: the possibility of using a single microorganism for the study of resistance to different drugs, even cases of double and triple resistance; it is biologically safe for society in general as no new genetically–modified strains are needed for the experiments; it is homologous with other fungal species, and there is repetitiveness between different strains. In conclusion, we propose L. prolificans as a candidate for consideration as a fungal model for the study of resistance mechanisms against antifungal agents.     

Synthesis and biochemical characterization of new phenothiazines and related drugs as MDR reversal agents

Chemotherapy is one of the most important methods in the treatment of cancer. However, development of drug resistance during chemotherapy is the leading cause of treatment failure and decreased survival in cancer patients. Multidrug resistance (MDR) is one of the extensively studied forms of drug resistance for more than 30 years. The members of ATP-binding cassette protein family are responsible for multidrug resistance with P-glycoprotein as most representative transporter. To overcome multidrug resistance, pharmacological modulation of the transporters by efflux pump inhibitors seem to be the first choice, but preclinical studies did not lead to clinical applications. Therefore, a systematical research for pharmacophor structures is a promising strategy to increase the efficacy of those drugs still influencing multidrug resistance. In this study a range of phenothiazine derivatives was synthesizied with systematical variation of three molecule domains. The biochemical determination of multidrug resistance reversal activity was achieved with the crystalviolet assay on LLC-PK1/MDR1 cells. The results will be discussed considering of hypotheses in the literature directed to new structure-acitivity relationships to overcome drug resistance in the future.     

Reversal effect of Dioscin on multidrug resistance in human hepatoma HepG2/adriamycin cells

Multidrug resistance is a serious obstacle encountered in cancer treatment. Since drug resistance in human cancer is mainly associated with overexpression of the multidrug resistance gene 1 (MDR1), the promoter of the human MDR1 gene may be a target for multidrug resistance reversion drug screening. In the present study, HEK293T cells were transfected with pGL3 reporter plasmids containing the 2 kb of MDR1 promoter, and the transfected cells were used as models to screen for candidate multidrug resistance inhibitors from over 300 purified naturally occurring compounds extracted from plants and animals. Dioscin was found to have an inhibiting effect on MDR1 promoter activity. The resistant HepG2 cell line (HepG2/adriamycin) was used to validate the activity of multidrug resistance reversal by Dioscin. Results showed that Dioscin could decrease the resistance degree of HepG2/adriamycin cells, and significantly inhibit P-glycoprotein expression, as well as increase the accumulation of adriamycin in HepG2/adriamycin cells as measured by Flow Cytometric analysis. These results suggest that Dioscin is a potent multidrug resistance reversal agent and may be a potential adjunctive agent for tumor chemotherapy.     

肿瘤多药耐药逆转剂研究进展

化疗是治疗肿瘤的主要手段之一，多药耐药性的产生是肿瘤化疗中存在的主要问题。开发多药耐药逆转剂，逆转现有化疗药物的耐药性将是一种有效的治疗方法。目前已有多种多药耐药逆转剂处于基础和临床试验阶段。本文对近年来多药耐药逆转剂的研究概况做了简要阐述。     

The molecular targets of antitumor 2'-deoxycytidine analogues

Most antitumor 2'-deoxycytidine (dCyd) analogues, such as Ara-C (1-beta-arabinofuranosylcytosine) and gemcitabine (2'-deoxy-2',2'-difluolo-cytidine), have common antitumor mechanisms and metabolic pathways. These nucleosides are transported into tumor cells via specific nucleoside transporters (NT), and then phosphorylated toward each monophosphate form by dCyd kinase. Finally, tri-phosphate forms are enzymatically produced and efficiently inhibit DNA synthesis. It is believed that dCyd kinase is a very important activator of antitumor 2'-dCyd analogues and an attractive molecular target for biochemical modulation. Resistant cells established by continuous exposure to 2'-dCyd analogues in vitro have extremely high resistance as compared with parental cells, and their resistance indexes are sometimes increased between several hundred to thousand times. Such high resistance is generally attributed to deficiency of dCyd kinase activity, but the clinical resistance index of Ara-C-resistant patients is estimated to be increased a maximum of 20 times compared with non-treated patients. The differences between experimental and clinical resistances may be caused by different mechanisms of resistance. To clarify such resistance mechanisms, we carried out research focused on NT and dCyd kinase. Our results show that earlier resistant cells, that exhibited a 20 times lower resistance index, had a reduced NT activity but retained dCyd kinase activity. In contrast, dCyd kinase activity was deficient in later resistant cells that showed maximum resistance. Both NT and dCyd kinase activities are important for the acquisition of resistance and are useful as molecular targets for biochemical modulation or the development of novel antitumor 2'-dCyd analogues. These results suggest that NT activity is likely to be responsible for clinical resistance.     

Inhibiting conjugation as a tool in the fight against antibiotic resistance

Antibiotic resistance, especially in gram-negative bacteria, is spreading globally and rapidly. Development of new antibiotics lags behind; therefore, novel approaches to the problem of antibiotic resistance are sorely needed and this commentary highlights one relatively unexplored target for drug development: conjugation. Conjugation is a common mechanism of horizontal gene transfer in bacteria that is instrumental in the spread of antibiotic resistance among bacteria. Most resistance genes are found on mobile genetic elements and primarily spread by conjugation. Furthermore, conjugative elements can act as a reservoir to maintain antibiotic resistance in the bacterial population even in the absence of antibiotic selection. Thus, conjugation can spread antibiotic resistance quickly between bacteria of the microbiome and pathogens when selective pressure (antibiotics) is introduced. Potential drug targets include the plasmid-encoded conjugation system and the host-encoded proteins important for conjugation. Ideally, a conjugation inhibitor will be used alongside antibiotics to prevent the spread of resistance to or within pathogens while not acting as a growth inhibitor itself. Inhibiting conjugation will be an important addition to our arsenal of strategies to combat the antibiotic resistance crisis, allowing us to extend the usefulness of antibiotics.     

Chromosomally-encoded resistance mechanisms of Pseudomonas aeruginosa: therapeutic implications

Pseudomonas aeruginosa is an important nosocomial pathogen that presents a difficult therapeutic challenge. Although P. aeruginosa has been shown to acquire resistance mechanisms encoded on plasmids, this pathogen comes armed with multiple chromosomally-encoded mechanisms of resistance that can provide impressive intrinsic resistance, as well as the potential to mutate to high-level multi-drug resistance. Recent analysis of the sequenced genome of P. aeruginosa PAO1 suggested that we have just started to unlock the resistance potential of this pathogen. One of the most serious threats to the usefulness of beta-lactams against P. aeruginosa is the chromosomal AmpC cephalosporinase. When AmpC production increases through mutational events, overproduction of this cephalosporinase provides high-level resistance to all beta-lactams except the carbapenems. Carbapenem resistance typically requires down-regulation of the outer membrane protein (OprD), which serves as the primary route of entry for carbapenems. Perhaps the most threatening of the resistance mechanisms encoded on the P. aeruginosa chromosome are the multi-drug efflux pumps. These pumps have the ability to extrude multiple classes of antibiotics from the periplasmic space, as well as the cytoplasm. Natural expression of efflux pumps in 'wild-type' cells plays an important role in the relatively decreased susceptibility of P. aeruginosa to antibiotics. However, the greatest therapeutic problems occur when these pumps are overproduced in mutants and high-level, multi-drug resistance develops. Although the development of infections with highly resistant strains of P. aeruginosa can present serious therapeutic challenges, the most troublesome threat associated with the chromosomally-encoded resistance mechanisms is the potential for high-level resistance to emerge during the course of therapy. When resistance emerges during therapy, clinical failure can occur and the therapeutic options for second-line therapy can become severely limited. Unfortunately, the emergence of resistance during therapy is not a rare event with P. aeruginosa and these three resistance mechanisms. Therefore, clinicians must be mindful of this threat when choosing an appropriate therapy, and usually appropriate therapy includes a combination of drugs. Since the standard combination of an aminoglycoside and a beta-lactam has been shown to be ineffective in preventing the emergence of some resistance problems, the search for more effective combinations must be a priority.     

IS INSULIN RESISTANCE LINKED TO HYPERTENSION?

1. The volume of work reporting insulin resistance in multiple forms of chronic hypertension has generated tremendous interest in whether this abnormality is an important factor in causing hypertension. Insulin resistance, however, is an imprecise term used interchangeably to describe widely disparate types of impairment in insulin action throughout the body and the type of insulin resistance has major ramifications regarding its potential for inducing long-term increases in blood pressure (BP). 2. Hepatic insulin resistance (impaired insulin-mediated suppression of hepatic glucose output) is the primary cause of fasting hyperinsulinaemia and is a cardinal feature of obesity hypertension. Evidence from chronic insulin infusion studies in rats suggests hyperinsulinaemia can increase BP under some conditions; however, conflicting evidence in humans and dogs leaves in question whether hyperinsulinaemia is a factor in hypertension induced by obesity. 3. Peripheral insulin resistance (impaired insulin-mediated glucose uptake, primarily of an acute glucose load in skeletal muscle) also present in obesity hypertension, but now reported in lean essential hypertension as well, is linked most notably to impaired insulin-mediated skeletal muscle vasodilation. This derangement has also been proposed as a mechanism through which insulin resistance can cause hypertension. 4. The present review will discuss the lack of experimental or theoretical support for that hypothesis and will suggest that a direct link between insulin resistance and BP control may not be the best way to envision a role for insulin resistance in cardiovascular morbidity and mortality.     

Molecular basis of antimicrobial resistance in Mycoplasma genitalium

Mycoplasma genitalium is a sexually transmitted urogenital pathogen, and infection can result in serious symptoms. As M. genitalium is rather difficult to culture, infections are usually detected by molecular methods. Unfortunately, there has recently been a significant increase in resistance to azithromycin and moxifloxacin used for the treatment of M. genitalium infections. The increased resistance to (often empirically prescribed) M. genitalium treatments has resulted in frequent therapy failures and stresses the need for routine detection of antimicrobial resistance. In M. genitalium, antimicrobial resistance is almost always the result of DNA mutations and thus can easily be detected by molecular techniques. Regrettably, many microbiology laboratories do not use molecular techniques for the detection of bacterial antimicrobial resistance. As molecular tests are becoming available for M. genitalium, both for the establishment of infection and the detection of antimicrobial resistance, it is now more important to ensure that knowledge on the resistance mechanisms is transferred from the laboratory to the clinician. This review will provide a brief summary of the current status of antimicrobial resistance, its molecular mechanisms and the impact on the current status of M. genitalium treatment.     

Antibiotic resistance

Antibiotic resistance is an increasing problem in many parts of the world. Antibiotic resistance has been associated with the use of some antibiotics but not with others. Due to the overuse of antibiotics with a high resistance potential, there has been an increase of resistance with certain bacteria, e.g., Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pneumoniae. This article discusses the antibiotics associated with a high resistance potential and those that are safe to use with a low resistance potential. Strategies for minimizing antibiotic resistance are discussed.