Drug resistance in human pathogenic fungi

Since the therapy of the mycoses, particularly the systemic mycoses, is relatively long-term in nature, emergence of resistance to antifungal drugs during the treatment of period would be of considerable clinical importance. However, most reports of resistance to antifungal agents among human pathogenic fungi indicate that naturally-occurring resistance is very rare, and that the induction of resistant mutants or variants is much more difficult to achieve in vitro and in vivo than with bacteria. As a matter of fact, amphotericin B and some other classic antifungals have not as yet posed a broadly significant problem relative to drug resistance despite their widespread and frequent use. Fungal resistance has thus received little attention, in contrast to the critical importance of bacterial resistance frequently caused by a variety of antibacterial chemotherapeutic agents, until a single exception to this generalization arose with the advent of flucytosine. This new development has aroused great interest in the problem of fungal resistance among the scientists involved with medical mycology. It is generally believed that fungi, like bacteria, are intrinsically capable of developing resistance to antifungal agents. As illustrated by flucytosine, inherently resistant mutants to antifungals occur within sensitive strains of human pathogenic fungi with significant frequency. Given the relatively high degree of such primary resistance, these mutants should develop secondary resistance during therapy, thus resulting in considerable limitations in the clinical usefulness of the antifungals. Virtually, all unsuccessful cases of mycoses treated with some of the recently exploited antifungal drugs, albeit scarce to date, would obviously be attributable to the occurrence of secondary resistance. The exploitation of new antifungal drugs thus requires investigations of their resistance as one of the most important research projects to be undertaken before receiving approval for use on humans. This paper reviews from various aspects the literature on resistance to various classic and novel antifungal agents among human pathogenic fungi. The resistance of some nonpathogenic fungi to these agents will also be described from genetic and biochemical points of view.     

Systemic mycoses in the immunocompromised host: an update in antifungal therapy

Despite significant advances in the management of immunosuppressed patients, invasive fungal infections remain an important life-threatening complication. In the last decade several new antifungal agents, including compounds in pre-existing classes (new generation of triazoles, polyenes in lipid formulations) and novel classes of antifungals with a unique mechanism of action (echinocandins), have been introduced in clinical practice. Ongoing and future studies will determine their exact role in the management of different mycoses. The acceleration of antifungal drug discovery offers promise for the management of these difficult to treat opportunistic infections.     

Antifungal activities of novel non-azole molecules against S. cerevisiae and C. albicans

Because of the increasing number of immunocompromised patients and due to problems with antifungal treatment, especially with the most widely used antifungals, azoles, there is an urgent need for new, potent and safe antifungals with fewer cytochrome P450 (CYP)-mediated interactions with other drugs. In the present study, 54 novel non-azole molecules were selected with the help of molecular modelling and virtual molecule database screening to identify new fungistatic or fungicidic compounds with functional groups that would produce reactive intermediates killing the yeast cells. Database screening and selection of tested compounds were based on the construction of two pharmacophores and docking hits to the active site of the CYP51 homology model. Inhibition potency of the compounds was tested against Saccharomyces cerevisiae and/or Candida albicans. Two new structured compounds, 2-({4-[(2-cyanoethyl)(methyl) amino]benzylidene} amino)-5-(3,4-dimethoxyphenyl)-4-methylthiophene-3-carbonitrile and 2-[([1,1'-biphenyl]-4-ylmethylene)amino]-5-(3,4-dimethoxyphenyl)-4-methylthiophene-3-carbonitrile were discovered to have promising antifungal properties based on bioassays. Inhibition screen of human hepatic CYP enzymes revealed that these two compounds did not inhibit potently five human recombinant CYP enzymes. The results of this study indicate that the functional groups of the two compounds may produce reactive intermediates when located at the active site of CYP51.     

Azole resistant Aspergillus fumigatus: An emerging problem

Azole resistance has appeared recently in Aspergillus fumigatus and increased dangerously in the last decade. The main resistance mechanism is a point mutation of CYP51A, the gene encoding 14α-sterol demethylase, the target enzyme of azole antifungal drugs. This mutation can induce resistance to itraconazole alone or multi-azole resistance. CYP51A mutation can occur in two cases. The first usually concerns patients receiving long-term azole therapy, most of the time for chronic aspergillosis, and involves a wide range of mutations. The second is due to the use of azole fungicides in agriculture. The latter favors a single mutagenesis event: a substitution of leucine for histidine at codon 98 and the tandem repeat of a 34-base pair tandem sequence in the CYP51A gene promoter region. This confers cross-resistance to all azole antifungal drugs. This emerging and environmentally linked issue is of growing concern for the management of antifungal therapy. This mechanism of resistance was first described in the Netherlands and is now reported worldwide. It may have become the leading mechanism of azole resistance in A. fumigatus. Azoles are major agents for the treatment of aspergillosis, and the only oral antifungals. Infection with antifungal-resistant strains is correlated with treatment failure. This emerging phenomenon stresses the urgent need for new preventive strategies (controlled use of antifungals and azole prophylaxis), new diagnostic strategies (early detection of resistance), and new therapeutic strategies in the management of A. fumigatus infections.     

243株假丝酵母菌属MIC结果分析

目的分析临床常见假丝酵母菌属对常用抗真菌药物的耐药性。方法采用法国生物梅里埃公司提供的ATB FUNGS 2试验板条,测定243株临床常见假丝酵母菌属的最低抑菌浓度（MIC）值。结果243株假丝酵母菌属以白色假丝酵母菌为主,占64.6%,其他依次为光滑假丝酵母菌（14.4%）、热带假丝酵母菌（11.1%）、近平滑假丝酵母菌（5.8%）、克柔假丝酵母菌（4.1%）;上述5种常见假丝酵母菌对5-氟胞嘧啶、两性霉素B、氟康唑和伊曲康唑4种抗真菌药物均产生了耐药性,其中克柔假丝酵母菌耐药率较高,对4种抗真菌药物的耐药率分别为20.0%、50.0%、30.0%和40.0%;上述5种常见假丝酵母菌对伊曲康唑耐药率均较对氟康唑高。结论临床常见假丝酵母菌属对常用抗真菌药物已具有一定的耐药性,应加强监测与控制。     

Occurrence and risk factors of oral candidiasis treated with oral antifungals in seniors using inhaled steroids

Oral candidiasis (OC) is a frequent side effect of inhaled corticosteroids (iCSTs). This study estimated occurrence and significance of risk factors of OC treated with antifungals in users of iCSTs under conditions of normal use. This retrospective analysis used data drawn from drug insurance plan records in Quebec, Canada. The sample contained 27,000 seniors using anti-asthma medications during 1990. Three years of data (1989-1991) were searched for use of oral antifungals concurrent with exposure to iCSTs. A case-control study examined factors leading to increased probability of first incidence of OC in new users of iCSTs. Three-year occurrence for OC was 7%. Increased risk for a first occurrence of OC was significantly associated with higher doses of iCST, increased length of iCST exposure, use of antibiotics, use of oral steroids, having three or more prescribers, a history of use of both high and low strengths of iCST, and concurrent use of oral steroids and diabetes medications. The occurrence of OC is relatively high. Knowledge of factors leading to increased risk could facilitate the targetting of patients who need timely intervention, under conditions of normal use.     

东江东莞城区段水体中抗生素的含量与污染特征研究

目的 研究东江东莞城区段水体中大环内酯类、β-内酰胺类、喹诺酮类、林可胺类、磺胺类、四环素类、抗真菌类、硝咪唑类及氯霉素类等9类共32种抗生素的含量和分布特征。 方法 采用固相萃取-高效液相色谱-串联质谱法测定水样中抗生素的含量,并分析该段水体中抗生素的污染特征。 结果 在采样周期内,3个采样点分别检出大环内酯类、β-内酰胺类、喹诺酮类、林可胺类、磺胺类、抗真菌类及硝咪唑类等7类共10种抗生素,其中林可霉素及氟康唑检出率为100%,阿奇霉素最高检出浓度为265.1 ng/L。 结论 东江东莞城区段水体已受到抗生素的污染,抗生素总体浓度处于中等偏低水平,需加强对该水体中抗生素的定期监测,采取相应措施以减少水体中抗生素残留污染。     

Infection control measures to prevent hospital transmission of candida

ABSTRACT

Invasive candida infections are the most important causes of nosocomial infections in intensive care units and in risky groups such as immunosuppressed patients. These infections lead to undesirable consequences such as increased morbidity and mortality in patients, prolongation of hospital stay, and increased hospital costs. In recent years, the incidence of non-albicans Candida spp.’s has increased. Unfortunately, some of these species are naturally resistant to first-line antifungals. In addition, biofilm formation on the central venous catheter and invasive devices may cause treatment failure. The age of the patients, co-morbid diseases, the units where they are treated, the antibiotics and antifungals that are used for the treatment, and invasive devices are risk factors for invasive candida infections. Some of these risk factors can be reduced by the behavior of health-care workers. The most important goal is to take precautions before the occurrence of invasive candida infections. Infection control measures to prevent hospital transmission of candida are very important. Compliance with hand hygiene before and after contact with the patient is the most important step to prevent the spreading of Candida spp. Observation of maximal barrier precautions during invasive catheterization is another important clause of this aim. Avoiding unnecessary invasive devices, antibiotics, and parenteral nutrition are also important to reduce the colonization of candida.     

Pruritic rash on trunk

The patient had been treated with topical antifungals and steroids without relief, but a more detailed history suggested a serious infectious etiology.     

临床标本的真菌培养和药敏分析

目的 研究本院真菌感染现状与耐药情况。方法 各种临床标本经分离培养，用ATB Expression细菌鉴定仪鉴定，采用ATB FUNGUS进行药敏试验。结果 13974份临床标本共分离真菌1535株，检出率为10．9％；分离真菌15种，白色念珠菌仍为主要菌种；各种真菌对6种抗真菌药物均出现了不同程度的耐药。结论 真菌感染在临床上呈上升趋势且产生了耐药株，临床微生物实验室不仅应做好真菌的分离培养鉴定，而且要对分离的菌株进行药敏试验，以指导临床合理选择抗真菌药物。     

Chronic paronychia--putting a finger on the evidence

At first glance it seemed a minor problem, but the look on my new patient's face suggested otherwise. His finger had been painful for months and this week it had become worse. His swollen, erythematous nail fold, absent cuticle, and mildly dystrophic nail painted a typical picture of chronic paronychia. Assuming an acute bacterial superinfection, I prescribed a course of antibiotics, but my patient needed advice on treatment of the underlying condition. Another general practitioner had arranged fungal cultures, which had grown candida. Would antifungals be the best treatment? My patient and I agreed to meet in a week to assess his response to the antibiotics and to discuss treatment of the underlying chronic paronychia.     

Disseminated Neocosmospora vasinfecta infection in a patient with acute nonlymphocytic leukemia

We report Neocosmospora vasinfecta infection following chemotherapy for acute nonlymphocytic leukemia. N. vasinfecta, a plant pathogen, was identified by culture and genetic sequencing. Susceptibility testing revealed in vitro resistance for common antifungals.     

白色念珠菌对临床常用抗真菌药物的耐药性分析

[目的]了解白色念珠菌对临床常用抗真菌药物的耐药性。[方法]按照美国临床实验室标准委员会(CLSI)推荐的酵母菌纸片扩散法敏感试验指南,对临床分离的852株白色念珠菌进行抗真菌药物的耐药性测定。[结果]852株白色念珠菌对两性霉素B、制霉菌素耐药率最低,分别为7.2%和12.6%,对伊曲康唑耐药率最高为78.5%;念珠菌常见临床感染部位为呼吸道,其次为尿道。[结论]白色念珠菌对常用抗真菌药物存在不同程度的耐药率,对送检标本及时进行真菌培养和药敏试验,合理使用抗生素和抗真菌药,减少多重耐药和深部真菌感染的发生。     

Recurrent vulvovaginal candidiasis

Widespread use of over-the-counter antifungal medications has contributed to a large increase in the number of women who experience more than three episodes of candida vulvovaginitis per year. These women are particularly prone to chronic vulvovaginal pain syndromes; as such, the value of aggressive therapy based on detailed diagnosis extends well beyond immediate symptom relief. Diagnosis is complicated by the fact that a larger proportion of cases of are due to non-albicans species, which are not readily identifiable at office evaluation, and points to the value of fungal culture in such cases. Although most Candida albicans are sensitive to azole antifungals, non-albicans species are more often resistant, necessitating alternative therapies. In many cases therapy aimed at suppression of recurrence must extend 6 months. Ongoing studies may identify host factors that facilitate recurrence, and thus provide the basis for individually targeted therapy.     

两性霉素B联合阿奇霉素及其他抗真菌药对烟曲霉体外抗菌活性研究 FREE

目的探讨两性霉素B（AMB）联合阿奇霉素（AZI）及其他常用抗真菌药对临床分离的30株烟曲霉体外抗菌活性,以指导临床治疗侵袭性曲霉病合理用药。方法药敏试验采用美国临床实验室标准化研究所（CLSI）制定的M38 A方案。结果抗真菌药体外抗菌活性依次为伏立康唑（VRC）0.29 μg/mL,卡泊芬净(CBF)0.45 μg/mL,伊曲康唑（ICZ）0.52 μg/mL,AMB 0.55 μg/mL。烟曲霉对特比萘芬（TBF）、5 氟胞嘧啶（5 FC）、氟康唑（FCZ）、AZI均显示耐药。联合用药有协同作用的为：AMB＋ICZ（96.67%）、AMB+VRC（90.00%）、AMB+CBF（83.33%）、AMB+5 FC(50.00%)。结论单独用药时,AMB、ICZ、VRC、CBF有很强的抗烟曲霉作用,烟曲霉对FCZ耐药,AZI无对抗烟曲霉作用;联合用药时,AMB与ICZ、VRC、CBF、5 FC有协同抗菌作用。对于侵袭性曲霉病,可选择AMB联合用药。     

Controversy concerning optimal prophylaxis and empirical antifungal therapy in immunocompromised patients

This article presents actual major problem about a steady increase in frequency of opportunistic invasive fungal infections (IFIs) in immunocompromised patients. However, there still remains much uncertainty regarding the best methods for establishing the diagnosis of most IFIs. An international consensus, that defining opportunistic IFIs proposed three levels of probability: "proven", "probable", and "possible". Practising physicians approach this uncertainty by prophylaxis and antifungal empirical therapy. Unfortunately, up to now we dispose only few antifungals compounds and all have narrow of therapeutic windows. This article reviews the therapeutic options in chemoprevention and antifungal therapy. Fluconazole and itraconazole are the first durable alternatives to polyenes in chemoprophylaxis. However their use remains controversial as debate continues over both their effectiveness and their potential to select out resistant Candida sp. Amphotericin B is the "gold" standard for the treatment both empirical and proven IFIs, but this drug is frequently associated with severe nephrotoxicity. The lipid formulations of amphotericin B enable higher dosages to be administrated with lower incidences of side effects but its effectiveness is not sufficient. It is to be hoped that rationally designed clinical trials with the new compounds, such as for example echinocandins will lead to improved prevention and treatment of IFIs.     

Azole-resistant Aspergillus fumigatus: A global phenomenon originating in the environment?

Aspergillus fumigatus is the predominant etiological agent of invasive aspergillosis (IA), a difficult-to-manage fungal disease associated with a high case fatality rate. Azole antifungals, particularly voriconazole, have significantly improved the survival rate of patients with IA. However, the clinical advances made possible through the use of medical azoles could be threatened by the emergence of azole-resistant strains which has been reported in an ever-increasing number of countries over the last 10 years. The major resistance mechanism, that combines point mutation(s) in the coding sequence of cyp51A gene and an insertion of a tandem repeat in the promoter region of this gene which leads to its overexpression (TR₃₄/L98H and TR₄₆/Y121F/T289A), is presumed to be of environmental origin. However, the emergence of clinical and environmental azole-resistant strains without the cyp51A gene mutation suggests that other mechanisms could also be responsible for azole resistance (for example, overexpression of efflux pumps). The development of resistance may be linked to either long-term use of azole antifungals in patients with chronic aspergillosis (patient-acquired route) or selection pressure of the fungicides in the environment (environmental route). The fungicide-driven route could be responsible for resistance in azole-naive patients with IA. This literature review aims to summarize recent findings, focusing on the current situation of azole-resistance in A. fumigatus, and provides better understanding of the importance of the environmental route in resistance acquisition.     

Selective Digestive Decontamination and its Use in Patients with Liver Disease

Selective digestive decontamination (SDD) involves the use of antibiotics to enhance the colonisation resistance of the gastrointestinal (GI) tract. This eradicates the Gram-negative organisms and fungi, if antifungals are used, which colonise the GI tract and subsequently cause infections in susceptible hosts. It has been used in patients who are critically ill and in intensive care units, in those who have multiple trauma or neutropenia and in bone marrow transplant recipients.SDD has been used in liver transplant patients perioperatively, in the prophylaxis of spontaneous bacterial peritonitis (SBP) and in acute liver failure. It has been shown to decrease the number of infections, specifically Gram-negative infections, in patients undergoing liver transplantation. SDD is very effective in the primary and secondary prophylaxis of SBP in cirrhotic patients with ascites. The use of the parenteral component of SDD is adequate in patients with acute liver failure. In both liver transplantation and SBP prophylaxis, mortality benefit has not been shown and the emergence of resistant organisms with the use of SDD is a concern.