抗菌药物防突变浓度及其临床意义

防突变浓度是指防止耐药突变菌株被选择性富集扩增所需的最低抗菌药物浓度。防突变浓度与MIC的浓度范围为突变选择窗。只有当血清或组织液药物浓度处于突变选择窗内时，才出现耐药突变菌株的选择性富集扩增，从而产生耐药。这一理论为有效抑制细菌耐药及制定抗菌药物应用策略提供了新的思路和参考依据。     

抗菌药物防突变浓度及其临床意义

防突变浓度是指防止耐药突变菌株被选择性富集扩增所需的最低抗菌药物浓度。防突变浓度与MIC的浓度范围为突变选择窗。只有当血清或组织液药物浓度处于突变选择窗内时 ,才出现耐药突变菌株的选择性富集扩增 ,从而产生耐药。这一理论为有效抑制细菌耐药及制定抗菌药物应用策略提供了新的思路和参考依据。     

细菌耐药突变选择窗与合理用药

耐药突变选择窗(mutant selection window,MSW)理论是近年来提出的一个遏制抗菌药物耐药的新策略,它从一个全新的角度来看待耐药性的产生,为预防耐药研究提供了新思路。同时MSW理论也对传统的抗感染药物开发策略提出了重要的修正,并为如何更好地通过联合用药来抑制耐药性的产生提供了新的理论依据与指导,已受到国内外学者的高度关注与重视。1MS W理论Baquero[1]在1990年首先提出抗菌药物存在一个最容易选择出耐药突变体的危险浓度区域。1999年Dong等[2]和Zhao等[3]在结核分支杆菌和金黄色葡萄球菌对氟喹诺酮类药物的耐药研究中确定了这…     

耐药突变选择窗与细菌耐药的动物体内研究

目的探讨耐药突变选择窗(MSW)与体内细菌耐药发生的相关性。方法建立兔组织笼金黄色葡萄球菌感染模型,给予不同剂量的左氧氟沙星灌胃治疗。抽取组织笼内组织液进行药物浓度测定,同时监测组织笼内细菌药物敏感性变化。结果当左氧氟沙星浓度位于MSW内时,导致金黄色葡萄球菌耐药突变体的选择富集,引起耐药。当药物浓度低于抑制菌群中99%细胞生长的最低药浓度或高于防耐药变异浓度时,无耐药出现。当左氧氟沙星浓度在MSW内的下部时,最容易选择出耐药突变体,且耐药出现最快。结论MSW在体内存在,保持抗菌药物浓度在MSW以上可以限制耐药突变体的选择富集。     

结核病治疗中利福平耐药金黄色葡萄球菌的筛选

获得性细菌耐药通常归因于感染部位抗菌药物浓度低于最低抑菌浓度（MIC），因此提倡抗菌药物浓度要高于MIC，从而清除敏感菌。但根据耐药突变选择窗（MSW）假说可以预测，即使药物浓度高于MIC，敏感菌被清除后仍会出现获得性细菌耐药。本课题旨在通过临床研究验证这一预测。     

金黄色葡萄球菌感染兔体内的耐药突变选择窗

耐药突变选择窗（MSW）假说是近年来提出的一个遏制抗菌药物获得性耐药的新策略，但到目前为止，这一假说还没有在动物体内被验证。     

单药及联合用药对金黄色葡萄球菌突变选择窗的影响

随着细菌耐药现象越来越严重，人们对细菌耐药机制的研究越深入，但主要集中在如何延缓获得性耐药的传播。Dong等1999年提出的防突变浓度（mutant prevention concentration，MPC）和突变选择窗（mutant selection window）的概念，则是用于体外判定药物是否可能导致病原菌产生自发耐药，为研究耐药机制开辟了新的领域。我们通过测定氟喹诺酮类药物单用及与头孢唑林联用对金黄色葡萄球菌ATCC29213株的最低抑菌浓度（MIC）MIC99和MPC，探讨联合用药对细菌突变选择窗的影响，寻找减少耐药突变菌株产生的新途径。     

左氧氟沙星单用及联合用药对细菌突变选择窗影响的研究

目的测定左氧氟沙星单用及分别与头孢哗林、头孢哌酮联用对金黄色葡萄球菌ATCC29213和大肠埃希氏菌ATCC25922的MIC99和防突变浓度（MPC）,探讨左氧氟沙星单药及联合用药对细菌突变选择窗（MSW）的影响,寻找减少耐药突变菌株产生的新途径。方法采用肉汤法富集1010CFU／ml金黄色葡萄球菌ATCC29213和大肠埃希氏菌ATCC25922,采用肉汤稀释法、琼脂平板稀释法体外测定左氧氟沙星单用及与头孢唑林联用对金黄色葡萄球菌标准株ATCC29213的MIC、MIC99、MPC,计算MPC／MIC99;测定左氧氟沙星单用及与头孢哌酮联用对大肠埃希氏菌标准株ATCC25922的MIC、MIC99、MPC,计算MPC／MIC99。结果左氧氟沙星单用对ATCC29213、ATCC25922的MPC分别为1．2μg／ml、0．125μg／ml,MPC／MIC99分别为13．27、9．54;左氧氟沙星与头孢唑林联用对ATCC29213的MPC为0．5／1．0μg／ml,MPC／MIC99为9．31;左氧氟沙星与头孢哌酮联用对ATCC25922的MPC为0．0375／0．146μg／ml,MPC／MIC99为7．98。结论左氧氟沙星与头孢唑林、头孢哌酮联合用药后能分别降低对ATCC29213、ATCC25922的MPC,同时缩小细菌突变选择窗,减少细菌对左氧氟沙星的耐药性产生。     

氟喹诺酮类药物对伤寒沙门菌的防突变浓度测定

氟喹诺酮类药物因具有良好的抗菌活性而成为治疗伤寒的首选药，但由于药物的不合理应用，出现了伤寒沙门菌对氟喹诺酮类药物的敏感度下降、甚至耐药。伤寒沙门菌对喹诺酮类药物的耐药性主要是通过编码靶位基因突变，导致DNA旋转酶结构改变，使药物不能与酶-DNA复合物稳定结合，从而产生耐药。而防耐药突变浓度（mutant prevention concentration，MPC）概念的提出，     

关注抗菌药物的防突变浓度

随着抗菌药物的广泛使用,细菌耐药问题变得越来越严重。为了减少细菌耐药,除了研究新型抗菌药物以外,近期把重点放在了建立在现有抗菌药物基础之上,以改变用药剂量或方法为特征的新的治疗策略上,提出了一些新的概念,其中颇为引人注目的是抗菌药物的防突变浓度(mutantprevention     

左氧氟沙星与加替沙星对肺炎克雷伯菌防耐药突变的比较

目的观察左氧氟沙星与加替沙星对肺炎克雷伯菌的防耐药突变作用。方法肉汤法富集受试菌菌液,接种含不同浓度左氧氟沙星及加替沙星琼脂平皿,测定左氧氟沙星、加替沙星对临床分离的肺炎克雷伯菌、ATCC700603及其耐药突变体的防耐药突变浓度;菌落计数法描绘菌落恢复生长曲线;测定ATCC700603及突变体的耐药突变窗及选择指数;结合药代动力学和药效动力学参数确定临床治疗方案。结果左氧氟沙星较加替沙星的防耐药突变浓度与细菌耐药选择指数大;菌落恢复生长曲线显示加替沙星的平台期窄于左氧氟沙星;加替沙星较左氧氟沙星的突变体耐药突变窗增宽幅度小。结论加替沙星防止肺炎克雷伯菌发生耐药突变作用强于左氧氟沙星。     

左氧氟沙星联合阿米卡星对肺炎克雷伯菌耐药突变选择窗的研究

目的探讨左氧氟沙星联合阿米卡星对肺炎克雷伯菌突变选择窗(MSW)的影响。方法琼脂倍比稀释法测定左氧氟沙星及其与阿米卡星联合对30株肺炎克雷伯菌的防突变浓度(MPC)和最低抑菌浓度(MIC),计算并比较左氧氟沙星单独及其与阿米卡星联合对肺炎克雷伯菌的选择指数(SI)。结果与阿米卡星联合,使左氧氟沙星对肺炎克雷伯菌的MPC范围由2～16 mg/l降至1～8 mg/L,MPC50由2 mg/L降至1 mg/L,MPC90由8 mg/L降至2 mg/L,P<0.01;左氧氟沙星单药及与联合阿米卡星对肺炎克雷伯菌的选择指数(SI)范围均在2～64,两组SI50均为16;SI90均为32,P>0.05;左氧氟沙星联合阿米卡星组较左氧氟沙星组SI降低的菌株有15株,无变化的有11株,增高的为4株。结论联合阿米卡星可降低左氧氟沙星对肺炎克雷伯菌的MPC,主要使左氧氟沙星对肺炎克雷伯菌的MSW变窄。     

Restricting the selection of antibiotic-resistant mutant bacteria: measurement and potential use of the mutant selection window

The selection of antibiotic-resistant mutant bacteria is proposed to occur in a drug concentration range (the mutant selection window) that extends from the minimum inhibitory concentration (MIC) of susceptible cells to the MIC of the least susceptible, single-step bacterial mutants (the mutant prevention concentration [MPC]). MPCs were estimated for tobramycin, chloramphenicol, rifampicin, penicillin, vancomycin, and several fluoroquinolones by use of Escherichia coli and Staphylococcus aureus. Comparisons among reported serum drug levels indicate that new fluoroquinolones are the least likely to enrich populations of resistant mutant bacteria during monotherapy. These data partly explain the selective enrichment of populations of resistant mutant bacteria in medical practice. The mutant selection window range (MPC:MIC) was narrowed for fluoroquinolones by structure modification, pointing to a new direction in antibiotic refinement. The mutant selection window and the MPC were determined for combinations of rifampicin and tobramycin, using S. aureus, as a guide for combination therapy with compounds that alone cannot block enrichment of mutant bacterial populations.     

The mutant selection window in rabbits infected with Staphylococcus aureus

BACKGROUND: The mutant selection window hypothesis, originally based on agar plate assays, may lead to new antimicrobial dosing strategies that severely restrict the acquisition of resistance. However, it has not been directly tested in an animal model of infection. METHODS: Local infection with Staphylococcus aureus was established in rabbits, and the infected animals were treated orally with various doses of levofloxacin. Changes in levofloxacin concentration, levofloxacin susceptibility, and counts of total and resistant viable bacteria were monitored at the site of infection. RESULTS: S. aureus lost levofloxacin susceptibility when drug concentrations at the site of infection fluctuated between the lower and upper boundaries of the window, defined in vitro as the minimum inhibitory concentration (MIC)(99) and the mutant prevention concentration (MPC), respectively. The upper boundary of the selection window in vivo was estimated as an AUC(24)/MPC value of ~25 h, where AUC(24) is the area under the drug concentration time curve in a 24-h interval. The lower boundary was estimated as an AUC(24)/MIC value of ~20 h. CONCLUSIONS: The mutant selection window exists in vivo, and its boundaries fit well with those determined in vitro. Maintenance of antimicrobial concentrations above the window is expected to suppress the outgrowth of resistant mutant subpopulations.     

Effect of low-level resistance on subsequent enrichment of fluoroquinolone-resistant Streptococcus pneumoniae in rabbits

BACKGROUND: We measured the effect of low-level fluoroquinolone resistance in Streptococcus pneumoniae on the development of high-level resistance within the context of the mutant selection window. METHODS: Rabbits infected with S. pneumoniae were treated with ciprofloxacin or moxifloxacin concentrations that simulated pharmacokinetics in treated humans; bacteria obtained from lungs were examined for fluoroquinolone susceptibility. RESULTS: Ciprofloxacin enriched resistant mutants from a wild-type strain; moxifloxacin did not. However, moxifloxacin enriched resistant mutants from a parC mutant; the drug concentration at the top of the selection window was determined. CONCLUSIONS: A parC resistance mutation facilitates the enrichment of high-level resistance, as was predicted by in vitro measurements.     

The pathophysiology of paroxysmal nocturnal hemoglobinuria

The molecular basis of PNH is known. Somatic mutation of the X-chromosome gene PIGA accounts for deficiency of glycosyl phosphatidylinositol-anchored proteins (GPI-AP) on affected hematopoietic stem cells and their progeny. However, neither mutant PIGA nor the consequent deficiency of GPI-AP provides a direct explanation for the clonal outgrowth of the mutant stem cells. Therefore, PNH differs from malignant myelopathies in which clonal expansion is directly attributable to a specific, monogenetic event (e.g., t(9;22) in CML) that bestows a growth/survival advantage upon the affected cell. Multiple, discrete PIGA mutant clones are present in many patients, suggesting that a selection pressure that favors the PNH phenotype (i.e., GPI-AP deficiency) was applied to the bone marrow. The nature of this putative selection pressure, however, is speculative, as is the basis of clonal expansion. In many patients, the majority of hematopoiesis is derived from PIGA mutant stem cells. Yet clonal expansion is limited (nonmalignant), and the contribution of the mutant clones to hematopoiesis may remain stable for decades. Understanding the basis of clonal selection and expansion will not only delineate further the pathophysiology of PNH but also provide new insights into stem cell biology and suggest novel therapeutic strategies for enhancing marrow function.     

Molecular epidemiology of malaria in Cameroon. XIV. Plasmodium falciparum chloroquine resistance transporter (PFCRT) gene sequences of isolates before and after chloroquine treatment

Laboratory studies have strongly suggested that the gene coding for Plasmodium falciparum chloroquine resistance transporter (PFCRT) may play a determinant role in chloroquine resistance. A clinical study in Mali also found evidence for selection of the key PFCRT amino acid substitution, Lys76Thr, in patients who fail to respond to chloroquine treatment. To test the hypothesis that in vivo selection of mutant PFCRT alleles occurs after chloroquine treatment, PFCRT and merozoite surface antigen 2 (msa-2) polymorphisms were compared between 61 pretreatment and posttreatment paired samples from children with either clinical or parasitologic failure. There were six wild-type PFCRT alleles, 44 mutant alleles, and 11 mixed alleles among pretreatment isolates. All posttreatment parasites had mutant PFCRT alleles. Recrudescence accounted for 42 of 61 posttreatment infections, while 19 posttreatment infections were due to new infection (including all isolates with Lys-76 before treatment and Thr-76 after treatment). Seven pretreatment isolates with mixed PFCRT alleles had only Thr-76 on recrudescence, providing a direct evidence for in vivo selection for mutant PFCRT. Although the presence of mutant PFCRT alleles in pretreatment isolates is not predictive of chloroquine treatment failure, our data support the hypothesis that in vivo selection for recrudescent parasites carrying mutant PFCRT alleles occurs. These results may have important implications for the future surveillance of chloroquine resistance by the use of molecular markers.     

Micropapillary urothelial carcinoma of the urinary bladder: report of one case and review of the literature

In 1994 Amin et al. described an uncommon variant of urothelial carcinoma: the micropapillary carcinoma (MPC) .The MPC of the urinary bladder is rare, but has an aggressive clinical course. The optimal treatment strategy for this tumor appears to be early radical cystectomy. We report a case of MPC of the urinary bladder and review the literature.