结核分枝杆菌"不均一耐药株"的形态学变异及细胞壁缺陷

地点:保加利亚索非亚国立结核病治疗医院;目的:研究2株“不均一耐药”临床分离株和1株非“不均一耐药”分离株的形态学。所有分离株均来自新诊断的结核病人(TB),以及参考株H37Rv。不均一耐药分离株包含克隆相关的敏感菌和耐药菌,它们进一步用含药初代培养和最初来自用1%比例法诊断为敏感的结核病例菌株。分枝杆菌在Dubos液体培养基培养25天后用透射电镜观察。结果:和H37Rv、非“不均一耐药”株相比,2株“不均一耐药”分离株具有明显的多形性变异,经典型和细胞壁缺陷型同时存在。链霉素和异烟肼耐药突变株在电镜下主要表现为不典型颗粒状的L-形状,构成Dubos培养基上的L-型菌落。结论:包含不同耐药基因型的混合结核分枝杆菌群临床不均一耐药分离株和耐药突变株克隆均可观察到L-型的转化过程,提示细胞壁缺陷的L-期状态和耐药可能相关,也提示可能是耐药突变株能在体内存活的机制之一。     

脓肿分枝杆菌复合群对克拉霉素耐药基因的初步研究

目的 分析脓肿分枝杆菌复合群对克拉霉素的耐药特征,为临床正确选用克拉霉素及有效控制其耐药提供依据和新思路。方法 选取中国疾病预防控制中心国家结核病参比实验室保存的2016—2017年全国耐药监测菌株中,鉴定为脓肿分枝杆菌复合群的385株临床分离株作为研究对象。采用多靶位基因测序法进行菌种鉴定和耐药基因检测;采用微孔板稀释法对菌株进行药物敏感性试验(简称“药敏试验”),检测其对克拉霉素和阿米卡星的耐药情况,并分析耐药菌株的耐药基因突变情况。结果 385株脓肿分枝杆菌复合群中,218株为脓肿分枝杆菌[包括185株为erm(41)T28基因型和33株erm (41)C28基因型],163株为马赛分枝杆菌,4株为博莱分枝杆菌。脓肿分枝杆菌、马赛分枝杆菌对阿米卡星和克拉霉素的耐药率分别为2.8%(6/218)和6.4%(14/218)、4.3%(7/163)和10.4%(17/163)。其中,erm(41)C28基因型脓肿分枝杆菌培养3d和14d对克拉毒素的耐药率(均为9.1%,3/33)不变,未发生诱导耐药,而erm(41)T28基因型脓肿分枝杆菌的耐药率则由培养3d时的5.9%(11/185)上升为培养14d的98.4%(182/185),171株发生诱导耐药。31株获得性耐药菌株中,10株脓肿分枝杆菌及10株马赛分枝杆菌均在rrl基因的2058/2059位点突变,最常见突变类型分别为A2058C(6株脓肿分枝杆菌,3株马赛分枝杆菌)和A2058G (3株脓肿分枝杆菌,5株马赛分枝杆菌);另有9株对阿米卡星耐药的菌株在rrs基因的A1408G位点发生突变,其中7株同时对克拉霉素耐药。结论 erm(41)T28基因型脓肿分枝杆菌更易诱导克拉霉素耐药。脓肿分枝杆菌和马赛分枝杆菌最常见的获得性耐药突变位点是rrl基因的A2058C和A2058G。     

特雷唑来对结核分枝杆菌体外抑菌作用的初步研究

目的评价特雷唑来对不同耐药类型的结核分枝杆菌临床分离株的体外抑菌作用,为临床应用提供实验依据。方法采用微孔板观察法,测定特雷唑来对标准株H37Rv及临床分离的敏感、单耐药、多耐药、耐多药以及广泛耐药各20株(共100株)的MIC,再测定特雷唑来与7种常用抗结核药物联合使用时,对H37Rv和10株MTB临床分离株(敏感、单耐药、多耐药、耐多药以及广泛耐药各2株)的MIC,通过计算分级抑菌浓度指数(FICI),观察特雷唑来对结核分枝杆菌的体外抑菌作用以及与其他抗结核药物联合使用时是否有协同作用。结果 94.0%(94/100)的结核分枝杆菌临床分离株可被≤0.5mg/L的特雷唑来抑制生长,特雷唑来对敏感株、MDR菌株(耐多药和广泛耐药)及非MDR耐药菌株(单耐药和多耐药)的MIC差异无统计学意义(χ~2=0.578,P0.05)。特雷唑来与7种抗结核药物在体外联合使用时对结核标准菌株H37Rv和临床分离株均未表现出相关性。结论特雷唑来对结核分枝杆菌,尤其是耐多药和广泛耐药菌株,均有很好的体外抑菌作用,且与细菌对其他抗结核药物是否耐药无关。     

结核分枝杆菌耐喹诺酮临床分离株gyrA基因突变的研究

目的 了解结核分枝杆菌喹诺酮(quinolones)耐药株耐药基因突变情况，评价其应用价值。方法 通过16S rRNA聚合酶链反应-单链构象多态性(PCR-SSCP)技术分析77株分枝杆菌临床分离株；通过PCR-SSCP和直接测序技术分析结核分枝杆菌的gyrA基因突变的情况。结果 75株为结核分枝杆菌复合群。30株喹诺酮敏感株的gyrA基因的SSCP图谱中，11株与H37Rv相同，19株与卡介苗相同；与卡介苗gyrA基因的SSCP图谱相同的敏感株95位密码子为ACC，与H37Rv该图谱相同的敏感株95位密码子为AGC。45株喹诺酮耐药株中，34株(75．6％)gvrA基因SSCP图谱泳动异常，对25株泳动异常、出现频率较高耐药株测序证实15株(44．1％)为94位密码子GAC→GGC突变；10株(29．4％)为90位密码子GCG→GTG的突变。结论 结核分枝杆菌耐喹诺酮与gyrA基因突变有关，PCR-SSCP可能成为测定结核分枝杆菌耐喹诺酮类药基因型的快速、简便的方法。     

单链构象多态性与核酸杂交联合检测耐氧氟沙星的结核分枝杆菌

目的探讨聚合酶链反应-单链构象多态性分析（PCR-SSCP）并Southern杂交检测耐氧氟沙星（OFLX）结核分枝杆菌的可行性，并探索结核分枝杆菌对OFLX敏感与耐药的界限。方法（1）体外筛选人工诱变的耐OFLX的耐药突变株，并检测OFLX对这些耐药株的最低抑菌浓度（MIC）和最低杀菌浓度（MBC）。（2）扩增结核分枝杆菌的gyrA基因，包括H37 Rv1株、H37 Ra 1株、临床分离的OFLX敏感株10株及人工诱变的耐OFLX H37 Rv（17株）、H37Ra（17株）及临床分离菌株（51株）共计85株，并对此扩增产物进行SSCP分析及Southern杂交，对比观察耐OFLX结核分枝杆菌的核酸单链条带位移的变化。为了验证PCR-SSCP并Southem杂交结果的可重复性，对36株临床分离的耐OFLX菌株的耐药界限进行初步检测。结果经PCR-SSCP及Southern杂交，85株人工诱变的耐OFLX菌株，全部检测到gyrA基因突变。在OFLX 10μg／ml这一点上，明显地存在着一个结核分枝杆菌对OFLX敏感与耐药并存的交叉区。对36株临床分离的OFLX耐药菌的PCR-SSCP合并Southem杂交检测结果显示，对比标准株H37Ra，在临床分离的耐OFLX菌株间观察到了类似的因单链构象变化而引起的单链位移的结果。结论PCR-SSCP合并Southern杂交可以清晰地区分对OFLX敏感与耐药的菌株，以100μg／m1为界作为判别结核分枝杆菌对OFLX是否已经产生耐药的标准是适宜的。     

康乐霉素A体外抗结核活性的初步研究

目的发现新安莎类抗生素，康乐霉素A体外抗结核活性。方法应用色谱技术从地中海诺卡氏菌康乐变株1747-64发酵液中分离康乐霉素A，并采用试管二倍稀释法，进行康乐霉素A对耻垢分枝杆菌（ATCC14468），结核分枝杆菌H37Rv（ATCC27294），H37Ra（ATCC25177），临床分离的氧氟沙星（OFLX）敏感结核分枝杆菌以及临床分离的耐氧氟沙星结核分枝杆菌最低抑制浓度（Minimal Inhibitor Concentration，MIC）的试验。结果康乐霉素A对耻垢分枝杆菌活性弱，MIC为64μg／ml，对结核分枝杆菌H37Rv，H37Ra的MIC为8μg／ml，对临床分离的氧氟沙星敏感结核分枝杆菌菌株的MIC范围为1～8μg／ml，临床分离的耐氧氟沙星结核分枝杆菌菌株的MIC范围为1～16μg／ml。结论新安莎类抗生素，康乐霉素A体外具有明显的抗结核活性，有望成为新抗结核药物或先导化合物。     

耐异烟肼和链霉素的结核分枝杆菌临床分离株与敏感株差异蛋白表达研究

目的 鉴定结核分枝杆菌对异烟肼和链霉素耐药相关的潜在蛋白。 方法 以药物敏感株（01105）和标准株H37Rv为对照,核素标记相对和绝对定量(isobaric tags for relative and absolute quantitation, iTRAQ)结合Nano液相色谱-串联质谱分析仪（LC-MS-MS）技术和生物信息学,鉴定并相对定量结核分枝杆菌对异烟肼与链霉素耐药的临床分离株02166菌体蛋白。 结果02166菌株分别与01105菌株和H37Rv菌株比较差异表达蛋白为153个和130个,02166菌株与01105菌株和H37Rv比较差异表达蛋白均为86个(共同差异表达蛋白)。差异表达蛋白理论相对分子质量和等电点分布广泛,相对分子质量从7.63~326.22,等电点从3.74~12.48,其主要参与中间代谢、呼吸作用和脂类代谢。共同差异表达蛋白：9个核糖体蛋白（Rv0056、Rv0651、Rv0652、Rv0701、Rv0719、Rv1630、Rv2785c、Rv2909c和Rv3458c）在02166菌株中表达下调;5个蛋白（Rv0234c、Rv2466c、Rv2626c、Rv2986c和Rv3118）在02166菌株中呈显著差异表达,其中琥珀酸半醛脱氢酶（Rv0234c）和假定未知蛋白（Rv2466c）在02166菌株中表达上调倍数>1.2,DNA结合蛋白HU同系物hupB（Rv2986c）、假定未知蛋白(Rv2626c和Rv3118)在02166菌株中表达下调倍数<0.5。 结论iTRAQ发现了耐异烟肼和链霉素的结核分枝杆菌临床分离株差异表达蛋白,为进一步探讨结核分枝杆菌异烟肼或链霉素耐药机制奠定了基础。     

耐异烟肼结核分枝杆菌临床分离株耐药相关基因突变研究

目的阐明结核分枝杆菌耐异烟肼临床分离株katG、inhA、ahpC、kasA及oxyR基因突变特点。方法对144株结核分枝杆菌临床分离株(耐异烟肼菌株101株;异烟肼敏感株43株)的katG、inhA、kasA、ahpC及oxyR基因进行DNA片断扩增及DNA序列分析,与GeneBank中结核分枝杆菌标准序列进行比较。结果(1)耐异烟肼菌株中未发现katG完全缺失,81株耐药株(80.2%)katG存在点突变、缺失或插入,其中16个突变位点未见报道;39株(38.6%)耐药株第315位点突变,低耐药菌株(1μg/ml)第315位点突变率显著高于高耐药菌株(10μg/ml;χ2=9.31,P<0.05);58株(57.4%)耐药株第463位点突变。23株(53.3%)敏感株第463位点突变。(2)5株(4.9%)耐药株inhA发生突变。敏感株inhA无突变。(3)3株(2.9%)耐药株ahpC发生突变。敏感株ahpC无突变。(4)17株(16.8%)耐药株kasA发生突变。敏感株中3株菌株Gly312Ser突变。(5)在全部菌株中未发现oxyR基因突变。(6)综合本项研究中各基因的突变情况,共有91株耐异烟肼菌株发生与异烟肼耐药相关的突变。结论本项研究进一步证实了结核分枝杆菌耐异烟肼与katG、inhA、ahpC及kasA基因突变之间的关系,并且提示还有其他机制参与异烟肼耐药。     

对氨基水杨酸（PAS）耐药与结核分枝杆菌thyA基因突变的研究

目的 检测结核分枝杆菌临床分离株对氨基水杨酸（PAS）耐药和胸苷酸合成酶基因（thyA）突变的关系，以探讨结核分枝杆菌PAS耐药的分子机制。方法95株结核分枝杆菌临床分离株中的51株PAS敏感株和44株PAS耐药株的PAS耐药相关基因thyA基因进行PCR扩增，扩增产物纯化后进行序列测定，与结核分枝杆菌标准株H37Rv的野生型岫，A基因序列进行对比，判断这些临床分离株的thyA基因有无突变。结果51株PAS敏感株thyA基因未检出突变。44株PAS耐药株中有16个临床分离株的thyA基因检测到突变，突变检出率为36．4％（16／44）。突变类型包括置换、颠换、插入、缺失，均为单碱基改变或单碱基缺失，其中2株为thyA基因2个位点联合突变。结论结核分枝杆菌tyA基因突变是其产生PAS耐药的重要原因之一。结核分枝杆菌胸苷酸合成酶是PAS作用的重要靶位。     

耐氧氟沙星的结核分枝杆菌临床分离株的gyrA基因点突变特点

目的研究结核分枝杆菌临床分离株的gyrA基因点突变位点和突变频率,了解目前结核分枝杆菌临床分离株耐喹诺酮类药物的基本特点。方法以我室保藏H_(37)Rv(ATCC272294),H37Ra (ATCC251 77)菌株以及由我所参比实验室提供的具有在改良罗氏培养基上获取的、对氧氟沙星     

结核分枝杆菌耐利福平药物机理的初步研究

目的通过诱导试验观察结核菌产生耐利福平药物的全过程,初步分析结核菌耐该药的机理。方法采用诱导试验、聚合酶链反应—单链构象多态性(PCR-SSCP)和序列分析,对经不同药物浓度传代培养后的结核菌强毒株（H₃₇Rv）和36株临床耐药分离株进行分析。结果在诱导到第7代时,H₃₇Rv的PCR-SSCP电泳出现异常,经测序证实在513位点发生基因突变。36株临床耐药分离株中有23株发生突变,为63.9% (23/36);其中有5株与诱导株基因突变位点相同。结论用药物不间断的刺激结核菌,是产生结核菌耐利福平药物的重要原因。     

Emergence of resistance to clarithromycin during treatment of disseminated cutaneous Mycobacterium chelonae infection: case report and literature review.

Results of in vitro susceptibility studies and one clinical trial have led to recommendations of clarithromycin monotherapy for the treatment of disseminated cutaneous Mycobacterium chelonae infections. We describe the case of a 65-year-old woman, immunocompromised by the use of chronic steroid therapy, who developed disseminated cutaneous infection with M. chelonae and failed clarithromycin monotherapy due to the development of drug resistance. In the relapse isolate we document the presence of a single point mutation at position 2058 in the gene coding for 23S rRNA peptidyltransferase regions, a mutation previously implicated in the development of resistance to clarithromycin. Two susceptible control isolates lacked the mutation. Three additional reports in the literature of patients developing recurrent skin lesions with clarithromycin-resistant M. chelonae following initial response to monotherapy are summarized. We demonstrate that clarithromycin monotherapy in patients with disseminated cutaneous infections can lead to clarithromycin resistance and therapeutic failure associated with a single point mutation at position 2058 of 23S rRNA.     

Changing pattern of antimicrobial resistance of <Emphasis Type="Italic">Helicobacter pylori</Emphasis> in Korean patients with peptic ulcer diseases

BACKGROUND: Antibiotic resistance of Helicobacter pylori is problematic because it reduces the efficacy of eradication therapy. It has been suggested that the incidence of resistance is rising. In Korea, information on the antimicrobial resistance of H. pylori is rare. The aim of this study was to assess the prevalence of H. pylori antibiotic resistance at a single center in Korea, and the changes in its antimicrobial resistance, and to detect the mutation foci of clarithromycin-resistant strains. METHODS: H. pylori isolates obtained from 224 patients with peptic ulcer disease in Korea between June 1996 and March 2000 were tested for antimicrobial resistance. The minimum inhibitory concentration (MIC) for metronidazole and clarithromycin was determined by the broth microdilution method. Isolates were considered resistant when the MIC was more than 8 microg/ml for metronidazole and more than 1 microg/ml for clarithromycin. To detect H. pylori 23S rRNA mutations, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was performed. Sequencing was performed on the two strands of the nonrestricted amplicons. RESULTS: Overall, resistance to metronidazole and clarithromycin was detected in 41.9% and 5.4% of patients, respectively. There was no significant difference in metronidazole and clarithromycin resistance according to age group and sex. Six strains were resistant to both metronidazole and clarithromycin. Six of nine clarithromycin-resistant isolates possessed the A2144G mutation in the gene encoding 23S rRNA. Sequencing of the three non-restricted clarithromycin-resistant strains revealed a T-to-C mutation at position 2182. CONCLUSIONS: In Korea, there was no significant increase in the prevalence of metronidazole resistance, but clarithromycin-resistant H. pylori strains had increased relatively over the 5-year period. There was an increasing tendency for the emergence of strains with dual resistance to metronidazole and clarithromycin. Many of the clarithromycin-resistant strains possessed the A2144G mutation.     

Molecular basis of clarithromycin-resistance in Mycobacterium avium intracellulare complex.

Nucleotide sequences of domain V and domain II regions of the 23S rRNA gene were determined in both in vitro-made mutants and clinical isolates of Mycobacterium avium and M. intracellulare conferring clarithromycin-resistance. All laboratory-made mutants showed high level resistance to clarithromycin (> 150 micrograms ml-1) and mutation at position 2058 (cognate with Escherichia coli base) in domain V region. In the clinical isolates, while the susceptible ones had no mutation in domain V, the resistant strains showed mutation at 2058 or 2059. Six isolates with low level of resistance exhibited no mutation in domain V. All strains tested had no mutation in domain II region. These results suggested that most of the resistance arose from the mutation in domain V of the 23S rRNA gene, but other unknown mechanisms evidently exist in mycobacteria.     

单耐氧氟沙星的结核分枝杆菌耐药机制研究

目的探讨单耐氧氟沙星的结核分枝杆菌中耐药相关基因突变及外排泵基因风坦两种不同耐药机制的作用。方法从国家结核病参比实验室2007年全国耐药基线调查菌株库中挑选单耐氧氟沙星的菌株17株。采用直接测序法检测利福平耐药相关基因删似和gyrB突变情况。提取gyrA和gyrB无突变菌株的RNA后反转录并采用Real—timePCR方法检测20个药物外排泵基因的表达量，对比菌株最低抑菌浓度（MIC）试验结果，筛选可能与氧氟沙星药物外排泵的相关基因，并选用大肠埃希菌为模式生物构建表达载体，检测过表达目的外排泵蛋白的大肠埃希菌对氧氟沙星的耐药程度加以验证。结果在17株单耐氧氟沙星的菌株中，有4株（4／17）检测到gyrA突变，其中包括90位点突变1株及94位点突变3株，上述突变均表现为高浓度耐药，其MIC均不低于4μg/ml。在gyrA和gyrB未突变菌株中，通过real-timePCR检测发现在高浓度耐药的2株菌株中，Rv0933和Rv2938的转录水平显著高于其他低浓度耐药菌株，较对照株H37Rv转录水平高16倍和5倍。在对照组和转入pEASY-E1-Rv2938的大肠埃希菌中MIC均小于0．125μg／ml，而转入pEASY-E1-Rv0933的大肠埃希菌的MIC为2μg／ml。结论本研究结果显示，gyrA耐药决定区基因突变与氧氟沙星高浓度耐药相关，PstB可能是氧氟沙星特异性的药物外排泵基因，其高水平表达与氧氟沙星高浓度耐药相关。     

Characterization of clarithromycin resistance in Malaysian isolates of Helicobacterpylori

AIM： To characterize the types of mutations present in the 23S rRNA genes of Malaysian isolates of clarithromycin-resistant Helicobacter pylori （H pylorl~. METHODS： Clarithromycin susceptibility of H pylori isolates was determined by E test. Analyses for point mutations in the domain V of 23S rRNA genes in clarithromycin-resistant and -sensitive strains were performed by sequence analysis of amplified polymerase chain reaction products. Restriction fragment length polymorphism was performed using Bsa I and MboI enzymes to detect restriction sites that correspond to the mutations in the clarithromycin- resistant strains. RESULTS： Of 187 isolates from 120 patients, four were resistant to clarithromycin, while 183 were sensitive. The MIC of the resistant strains ranged from 1.5 to 24 pg/mL. Two isolates had an A2142G mutation and another two had A2143G mutations. A T2182C mutation was detected in two out of four clarithromycin-resistant isolates and in 13 of 14 clarithromycin-sensitive isolates. Restriction enzyme analyses with Bsa I and Mbo I were able to detect the mutations. CONCLUSION： Clarithromycin resistance is an uncommon occurrence among Malaysian isolates of Hpylori strains and the mutations A2142G and A2143G detected were associated with low-level resistance.     

Detection of genotypic clarithromycin-resistant Helicobacter pylori by string tests

AIM:To evaluate the utility of the string test to detect genotypic clarithromycin-resistant Helicobacter pylori (H.pylori)by polymerase chain reaction(PCR)-restriction fragment length polymorphism.METHODS:Patients undergoing endoscopic examinations were enrolled in the present study.String tests were done on the next day of endoscopy.Segments of 23S rRNA were amplified from DNA obtained from string tests.PCR-restriction fragment length polymorphism was accomplished by restriction enzymes BbsI and BsaI recognizing the mutation site A to G at 2143or at 2142 of 23S rRNA domain V,respectively.RESULTS:One hundred and thirty-four patients with H.pylori infection underwent string tests.To compare phenotypic resistance,43 isolates were successfully cultured in 79 patients in whom 23S rRNA was successfully amplified.Of five patients with clarithromycinresistant H.pylori,23S rRNA of H.pylori isolates from four patients could be digested by BsaI.In 38 susceptible isolates,23S rRNA of H.pylori isolates from 36 patients could not be digested by either BsaI or BbsI.The sensitivity and specificity of the string test to detect genotypic clarithromycin resistance were 66.7%and97.3%,respectively.Positive and negative predictive values were 80%and 94.7%,respectively.CONCLUSION:String test with molecular analysis is a less invasive method to detect genotypic resistance before treatment.Further large-scale investigations are necessary to confirm our results.     

克拉霉素耐药幽门螺杆菌株的基因型分布

背景：根除幽门螺杆菌（H.pylori）治疗在临床上的应用日益普遍。耐药菌株的出现是近年H.pylori根除率下降的主要原因,尤其是目前根除治疗作用最强的抗生素之一——克拉霉素。目的：研究克拉霉素耐药H.pylori菌株的基因型分布,为快速检出抗生素耐药提供基础。方法：以琼脂稀释法筛选出2002年9月～2003年2月13株原发性、22株获得性克拉霉素耐药H.pylori菌株,提取基因组DNA。聚合酶链反应（PCR）-反向斑点杂交法检测克拉霉素耐药H.pylori菌株23SrRNA基因中7种不同的点突变（A2115G、G2141A、A2142G、A2142C、A2143G、A2143C和A2142T）。结果：34株（97.1%）克拉霉素耐药H.pylori菌株发生A2143G突变,其中13株为原发性,21株为获得性;1株（2.9%）获得性耐药菌株发生A2142G突变。结论：我国克拉霉素耐药H.pylori菌株基因型以23SrRNA基因A2143G突变占主导地位,与欧美国家报道的A2142G和A2143G突变率相近不同。     

Comparison of clarithromycin-sensitive and clarithromycin-resistant Mycobacterium avium strains isolated from AIDS patients during therapy regimens including clarithromycin

OBJECTIVES: Sixteen Mycobacterium avium strains were isolated from the blood of eight AIDS patients over a period of months. All the patients were on combination therapies including clarithromycin, and all had treatment failure and relapses of M.avium bacteremia. Paired clarithromycin-sensitive and resistant M.avium strains isolated at the beginning of treatment and at the first relapse of bacteremia were compared. METHODS: The M.avium isolates were identified after hybridization with DNA probes specific for M.avium rRNA and typed epidemiologically with random amplified polymorphic DNA analyses using three arbitrary primers. The rate of intracellular cell entry or the tumour necrosis factor alpha induction by the M.avium isolates were studied in human monocytes and J774 cells. RESULTS: When the M.avium isolates were hybridized with the rRNA probes, we obtained lower hybridization values with clarithromycin-resistant isolates than with clarithromycin-sensitive isolates. This appeared to be due to smaller amounts of rRNA available for hybridization than to mutation of the 23S rRNA sequences in clarithromycin-resistant strains. The RAPD analyses showed that the clarithromycin-resistant isolates were clonally related to the clarithromycin-sensitive strains in six of the eight patients. The other two patients had a RAPD profile, suggesting a re-infection and/or polyclonal infection. The M.avium isolates obtained on day 0 and after the emergence of resistance to clarithromycin did not differ in terms of their intracellular entry rate, or in terms of tumour necrosis factor alpha induction. CONCLUSIONS: We infer that M.avium strains isolated during bacteraemic relapses on combination therapies including clarithromycin are epidemiologically related to the initial strain and do not show changes in the rate of intracellular cell entry and in terms of tumour necrosis factor alpha induction. Re-infections and/or polyclonal infections however, although less frequent, can also occur.     

Helicobacter pylori isolates from ethnic minority patients in Guangxi:Resistance rates,mechanisms,and genotype

AIM:To investigate the rate of Helicobacter pylori（H.pylori）resistance to clarithromycin among ethnic minority patients in Guangxi,explore the underlyingmechanisms,and analyze factors influencing genotype distribution of H.pylori isolates.METHODS:H.pylori strains were isolated,cultured and subjected to drug sensitivity testing.The 23S rRNA gene of H.pylori isolates was amplified by PCR and analyzed by PCR-RFLP and direct sequencing to detect point mutations.REP-PCR was used for genotyping of H.pylori isolates,and NTsys₂ software was used for clustering analysis based on REP-PCR DNA fingerprints.Factors potentially influencing genotype distribution of H.pylori isolates were analyzed.RESULTS:The rate of clarithromycin resistance was31.3%.A2143G and A2144G mutations were detected in the 23S rRNA gene of all clarithromycin-resistant H.pylori isolates.At a genetic distance of 78%,clarithromycin-resistant H.pylori isolates could be divided into six groups.Significant clustering was noted among H.pylori isolates from patients with peptic ulcer or gastritis.CONCLUSION:The rate of clarithromycin resistance is relatively high in ethnic minority patients in Guangxi.Main mechanisms of clarithromycin resistance are A2143G and A2144G mutations in the 23S rRNA gene.Clarithromycin-resistant H.pylori isolates can be divided into six groups based on REP-PCR DNA fingerprints.Several factors such as disease type may influence the genotype distribution of H.pylori isolates.