四川地区200例随机临床分枝杆菌分离株耐药状况的分析研究

目的 了解四川地区分枝杆菌的耐药状况,为临床用药提供参考依据.方法 采用罗氏绝对浓度法对我院2009年6月-2010年12月间的200株分枝杆菌随机临床分离株进行9种抗结核药物的敏感性试验,并同步进行微量药敏(MIC)检测.结果 200株分枝杆菌临床分离株中192株(96.0％)为结核分枝杆菌(MTB),8株(4.0％)为非结核分枝杆菌(NTM),两种分群方法结果一致.192株MTB中108株对9种抗结核药物全部敏感,对≥1种药物耐药者84株,总耐药率为43.7％ (84/192),多重耐药( MDR)23株(12.0％),广泛耐药4株(2.1％),全耐药2株(1.0％).耐9种不同抗结核药物的顺位由高到低依次为:丙硫异烟胺(PTA,33.3％)、异烟肼(INH,20.8％)、利福平(RFP,17.2％)、硫酸链霉素( SM,16.7％)、硫酸阿米卡星注射液(AMK,16.7％)、力克肺疾(PI,16.1％)、乙胺丁醇(EMB,10.9％)、左氧氟沙星( LFX,8.8％)、硫酸卷曲霉素(CPM,6.2％);单一耐1、2、3、4、5、6、7、8和9种药物耐药率分别为12.5％、7.3％、6.2％、4.7％、4.2％、3.6％、3.1％、1.0％和1.0％.对≥2种药物耐药者60株(31.2％);对≥4种药物耐药者34株(17.7％).M DR-TB对另外7种药物的罗氏药敏耐药率从高到底依次为:PI(78.3％)、EMB(69.6％)、SM(65.2％)、PTA (65.2％)、LFX (39.1％)、AMK( 30.4％)、CPM(8.7％).结论 四川地区耐药性结核病仍处于全国较高水平,特别是同时耐多种(≥4种)药物的耐药率较高,应引起重视.     

噬菌体生物扩增技术在结核分枝杆菌药敏检测中的应用

目的探讨噬菌体生物扩增技术（PhaB）在结核分枝杆菌（MTB）耐药研究中的应用价值。方法应用PhaB法同时测定233株结核分枝杆菌分离株对异烟肼（INH）、链霉素（SM）、利福平（RFP）及左旋氧氟沙星（LEV）的耐药性,并用改良罗氏培养法（LJ）做对照,比较两种方法的检测结果。结果PhaB法检测INH、SM、RFP、LEV的药敏结果与改良罗氏培养法药敏结果相比符合率分别为97．4％、96．6％、95．3％、96．9％。同时检出耐多药菌株26株,占11．1％。结论PhaB法能快速进行结核分枝杆菌的药敏检测并与金标法U符合率高,可作为基层结防单位MTB耐药性的快速筛选方法。     

快速检测结核分枝杆菌异烟肼和利福平耐药相关基因mPCR-SSCP建立及应用

目的 建立快速检测结核分枝杆菌异烟肼(INH)和利福平(RFP)耐药相关基因katG、inhA和rpoB突变的多重聚合酶链反应-单链构象多态性(multi PCR-single strand conformational polymorphism analysis,mPCR-SSCP)方法.方法 药敏试验检测134株结核分枝杆菌临床菌株对INH和RFP的耐药性.设计结核分枝杆菌INH和RFP耐药相关katG、inhA和rpoB基因PCR引物,建立mPCR-SSCP技术检测上述菌株katG、inhA和rpoB基因的突变,同时采用PCR直接测序技术(PCR-DS)检测上述基因片段突变情况,并对上述3种方法检测结果进行分析和比较.结果 134株临床菌株均含有katG、inhA和rpoB基因,其中42株(31.3％)对INH耐药、45株(33.6％)对RFP耐药.mPCR-SSCP和PCR-DS检测结果显示,92株INH敏感菌株katG和inhA基因均未发生突变,检测特异性均为100％;89株RFP敏感菌株中rpoB基因分别有2株和1株检测出突变,检测特异性分别为97.8％和98.9％;42株INH耐药菌株中分别有33株和36株katG和/或inhA基因突变,检测灵敏度分别为78.6％和85.7％;45株RFP耐药菌株中rpoB基因分别有41株和43株发生突变,检测灵敏度分别为91.1％和95.6％.结论 本研究建立的mPCR-SSCP能快速、简便、特异,并有一定的敏感性检测结核分枝杆菌异烟肼和利福平耐药相关基因katG、inhA和rpoB突变,具有临床应用前景.     

国产卫肺宁、卫肺特体内外抗结核菌作用研究

卫肺宁(二联)卫肺特(三联)对标准人型结核分枝杆菌H_(37)RV,牛型结核分枝杆菌和人工诱导耐RFP、SM的H_(37)Rv菌株、草分枝杆菌及临床分离的15株结核分枝杆菌(共20株结核分枝杆菌)的体外抗菌作用结果表明,卫肺宁、卫肺特在罗氏培养基中对H_(37)RV的MIC分别为0.39和0.1mg/L;对牛型结核分枝杆菌的MIC均为3.12mg/L;与单用利福平接近,比单用异烟肼稍弱,比单用吡嗪酰胺稍强。卫肺宁、卫肺特对草分枝杆菌的MIC均为100mg/L,对临床分离的17株人型结核分枝杆菌中15株的MIC为0.2～6.25mg/ml,其中2株MIC为25～100mg/L,国产卫肺宁、卫肺特与进口卫肺宁、卫肺特的抗结核分枝杆菌的作用基本一致。     

利血平对耐药结核分枝杆菌临床株的作用

目的观察泵抑制剂（利血平）对耐药结核分枝杆菌临床分离株的作用。方法应用3组BacT．ALERT3D培养仪系统的培养基。分别命名为A、B、C组培养基。3组培养基均接种42株耐药结核分枝杆菌临床分离株，其中A、B组同时加入利福平1μg／mL；环丙沙星2μg／mL；利福平1μg／mL和环丙沙星2μg／mL；A、C组同时加入利血平20mg／L：C组未加入任何抗结核药物。结果在A组培养基中，耐利福平1μg／mL的14株菌株中有2株恢复对利福平的敏感性，12株仍然耐药；耐环丙沙星2μg／mL的6株菌株和耐利福平1μg／mL及环丙沙星2μg／mL的22株菌株全部恢复药物敏感性。在B组培养基中，42株耐药结核分枝杆菌临床分离株．药物耐药性无变化。在C组培养基中，42株耐药结核分枝杆菌临床分离株明显生长，说明利血平对所研究菌株无抑制作用。A组与B组培养基细菌的药物敏感性差异有统计学意义（P〈0．01）。结论结核分枝杆菌存在耐药机制之一的外排系统；泵抑制剂之一利血平对耐药的结核分枝杆菌临床分离株有抑制其外排作用，使结核分枝杆菌恢复敏感性。     

251株分枝杆菌的分离培养及临床耐药性分析

目的从痰及体液等临床标本中分离培养出分枝杆菌并进行体外药物敏感性分析,为临床合理选用抗菌药物提供依据。方法采用绝对浓度间接法试验对251份培养阳性标本进行4种抗结核药物（INH、RFP、EMB、SM）的耐药性测定。结果总耐药率为60.96%（153）,初治耐药率为45.10%（69）,初治耐多药率为30.07%（46）,复治耐药率为85.71%（84）,复治耐多药率为56.12%（55）。耐药顺序为RFP﹥INH﹥SM﹥EMB,耐药率分别为49.80%、47.41%、25.10%、18.73%。结论本地结核菌耐药情况严重,因此应加强抗结核药物的耐药性监测,根据药敏结果选择有效化疗方案,彻底治疗结核病人。     

复方利福平(二、三联)的药效学试验

卫肺宁、卫肺特对标准人型结核分枝杆菌H_(37)Rv,牛型结核分枝杆菌和人工诱导耐RFP、SM的H_(37)Rv菌株、草分枝杆菌及临床分离的15株结核分枝杆菌(共20株结核分枝杆菌)的体外抗菌作用结果表明,卫肺宁、卫肺特在罗氏培养基中对H_(37)Rv的MIC分别为0.39和0.1mg/L;对牛型结核分枝杆菌的MIC均为3.12mg/L;与利福平单用接近,比异烟肼单用稍弱,比吡嗪酰胺单用稍强。卫肺宁、卫肺特对草分枝杆菌的MIC均为100mg/L,对临床分离的17株人型结核分枝     

M/XDR-TB的快速分子检测和耐药特征分析

目的 使用分子线性探针杂交技术结合仪器法液体快速培养分析耐多药( multidrug resistant,MDR)及广泛耐药(extensively drug resistant,XDR)结核分枝杆菌(Mycobacterium tuberculosis,MTB)的耐药基因和表型特征.方法 运用GenoType MTBDR试剂盒检测M/XDR-TB菌株中各耐药基因的突变位点及类型,平行用BD MGIT960系统检测所选菌株对一线及二线抗结核药物的敏感性.结果 (1)94株MDR-TB经MGIT960检测,乙胺丁醇(ethambutol,EMB)、阿米卡星(amikacin,AMK)、氧氟沙星(ofloxacin,OFX)及莫西沙星(moxifloxacin,MFX)的耐药率分别为36.2%、17.0%、54.3%和55.3%.XDR-TB检出率为13.8%.(2)以MGIT960药敏结果作为参考标准,94株MDR-TB中,GenoType MTBDRplus检测MTB对异烟肼(isoniazid,INH)、利福平(rifampin,RFP)耐药的符合率分别为86.2%和95.7%;GenoType MTBDRsl检测MTB对EMB、AMK、OFX及MFX耐药的敏感性分别为47.1%、81.3%、94.1%、94.2%;特异性分别为75.0%、98.7%、90.7%、92.9%.(3)rpoB基因突变中以S531L最多;INH耐药主要由katG基因发生突变导致,以S315T1类型居多;gyrA突变位点主要集中在第94位密码子.所测菌株中有23例为复合耐药,7例为未知突变.结论 M/XDR-TB中,INH、RFP、AMK、OFX及MFX耐药株大多分别是由katG、rpoB、rrs及gyrA突变导致,乙胺丁醇与embB之间的耐药关联性相对较低.GenoType MTBDR试剂盒检测M/XDR-TB敏感性和特异性较好,可以在未获得传统细菌表型药敏结果前指导临床用药治疗.     

显色法芯片检测结核分枝杆菌利福平和异烟肼耐药基因

目的建立显色法芯片检测结核分枝杆菌耐药基因的方法。方法设计4对地高辛标记引物,扩增结核分枝杆菌rpoB、katG、inhA和ahpC 4个基因部分片段,根据结核分枝杆菌利福平(RFP)和异烟肼(INH)4条耐药相关基因上8个位点的25种单核苷酸多态性设计探针制作芯片,扩增产物与芯片杂交,显色法判断结果;用该法检测46株结核分枝杆菌临床分离株。结果扩增产物琼脂糖电泳可见4条大小分别为165、181、245、315 bp DNA条带;结核分枝杆菌菌液浓度为1．6×103／ml时,该法仍可检测到各位点野生及突变信号;19种非结核分枝杆菌标准株和9种非分枝杆菌标准株扩增产物无DNA条带,与芯片杂交亦无信号,H37Rv结核分枝杆菌标准株芯片检测各位点均为野生型;5株结核分枝杆菌临床分离株重复检测5次,结果完全一致;6份PCR产物的测序结果与芯片检测结果完全一致;46株结核分枝杆菌临床分离株中,RFP耐药株28株,芯片检出突变株24株,突变率为85．7％,RFP敏感株18株,芯片检出突变株2株。INH耐药株31株,芯片检出突变株20株,突变率为64．5％,INH敏感株15株,芯片检出突变株4株。结论显色法芯片检测结核分枝杆菌耐药基因具有较高的敏感性和特异性,无需特殊仪器设备,有一定的推广应用价值。     

应用反向线性杂交技术快速检测结核分枝杆菌利福平耐药性研究

探讨反向线性杂交技术(reverse line blot assay,RLB)在结核分枝杆菌利福平(RFP)耐药性快速检测中的应用价值.采用RLB将包含rpoB基因核心区的扩增产物与标记特异性探针的膜进行杂交,共对121株结核分枝杆菌进行RFP耐药性检测,并将结果与常规药敏实验进行比较.结果发现,121株中有71株对RFP耐药,56株为多重耐药株;采用RLB共检测到65株RFP耐药株rpoB基因核心区存在突变,其灵敏度为91.5%(65/71);50株RFP敏感株中均未检测到突变,则特异性为100%(51/51);56株多耐药菌株中,92.9%(52/56)存在rpoB基因核心区突变.因此,用RLB检测结核分枝杆菌RFP耐药株具有快速,高效,特异性和灵敏度高的优点,且可用于多耐药菌株的筛选,具有推广和潜在的临床应用价值.     

Antimicrobial susceptibility testing for Mycobacterium tuberculosis by measuring mycobacterial adenosine triphosphate

The antimicrobial susceptibility test for Mycobacterium tuberculosis H37Rv and 43 clinical isolates was performed using a bioluminescence assay by measuring the content of adenosine triphosphate (ATP) derived from mycobacteria. The drugs tested were isoniazid (INH), rifampicin (RFP), ethambutol (EB), streptomycin (SM), and kanamycin (KM). The ATP contents of M. tuberculosis incubated in the Middle-brook 7H9 broth medium containing antituberculous agents were measured at days of 0, 1, 3, 5, 7 and 10. A reduction of ATP content, indicating growth inhibition, was observed in susceptible strains within 5 to 10 days of incubation. Optimal concentrations to distinguish between susceptible and resistant strains were determined as being INH 0.20, RFP 0.50, EB 5.0, SM 4.0, KM 6.0 g/ml. The agreements of ATP method (evaluated at 10 days) with Vite Spectrum and MIC determinations were 81.4% and 100%, respectively. Susceptibilities to most drugs, except for EB, could be determined within 7 days. This method is simple, rapid, nonradiometric, and can be used for drug susceptibility.     

Reliability of bioluminescent assay (ATP method) for testing antimicrobial susceptibility of Mycobacterium tuberculosis]

To evaluate the reliability of our previously reported antimicrobial susceptibility test by ATP method, we have compared our ATP method to the reference test methods such as Mycobacteria Growth Indicator Tube(MGIT) method, minimum inhibitory concentration(MIC) method, NCCLS M24-T agar proportion method(M24-T method), and Vite spectrum method. The concentrations of drugs used for the assessment were isoniazid(INH) 0.1 microgram/ml, rifampicin(RFP) 2.0 micrograms/ml, ethambutol(EB) 2.5 micrograms/ml, streptomycin (SM) 2.0 micrograms/ml, and kanamycin (KM) 5.0 micrograms/ml. When six M. tuberculosis ATCC strains were subjected to 6 independent experiments by using ATP method, highly reproducible results were obtained on the fifth day of the incubation. We examined correlation among ATP method and reference test methods in drug susceptibility testing for 65 clinical isolates of M. tuberculosis. The correlation between ATP method and MGIT-, MIC-, M24-T method were more than 95% for all drugs. When ATP method and Vite spectrum method was compared, the correlation was 87.7% for INH, 98.5% for RFP, 90.8% for EB, 92.3% for SM, 96.9% for KM. The culture period for determining susceptibility between ATP method and MGIT method was compared by using ATCC reference strains and clinical isolates. Six M. tuberculosis ATCC strains were subjected to 6 independent experiments. By the MGIT method, 8 days were required to obtain the results, whereas 3 days were enough by the ATP method. For 65 clinical isolates, the MGIT method required 9 days for determining susceptibility of all isolates. The ATP method required only 5 days for the same strains. These data demonstrate that the improved ATP method that we reported, is simple, rapid, highly reproducible and nonradiometric, and could be used for the assessment of drug susceptibility for M. tuberculosis with high reliability.     

分析5种结核杆菌耐药基因突变与耐药水平的关系

目的：分析5种结核杆菌（M.tb)耐药基因突变的情况，了解基因突变和耐药水平的关系。方法：134例临床分离株均做传统梯度药敏试验和聚合酶链反应－单链构象多态性I（PCR－SSCP）试验。结果：耐PZA(pncA),SM(rpsL),REP(rpoB),INH(katG),EMB(embB)基因突变率分别为42．7％、72％、78％、69％和43．9％，其中，上述高耐株基因突变率分别为70％、87．2％、93．4％、80％、43．9％。低耐株分别为12．5％、28．5％、45．4％、18．7％，EMB在低耐区无基因突变，结论：M.tb耐药基因变与耐药水平联系密切，多数M.tb耐药基因突变易发生在高耐药区，也有少数菌基因突变易发生在低耐药区。     

Microcolonies in fluoroquinolone agar proportion susceptibility testing of Mycobacterium tuberculosis: an indicator of drug resistance

Microcolony growth of Mycobacterium tuberculosis on agar proportion susceptibility testing is neither well-defined nor previously reported with fluoroquinolone susceptibility testing. We describe here M. tuberculosis microcolony growth with fluoroquinolones, and assess its clinical significance. We screened 797?M. tuberculosis isolates for ofloxacin resistance (2.0?μg/mL) by agar proportion; 19 ofloxacin-resistant and 38 ofloxacin-susceptible isolates were selected for more detailed susceptibility testing with ofloxacin, ciprofloxacin, levofloxacin (all at 2.0?μg/mL) and moxifloxacin (0.5?μg/mL). The 57 isolates were also tested at two concentrations both above and below the critical concentrations. Microcolonies were defined as colonies 0.2-0.4?mm in diameter; confirmed microcolonies were present on repeat testing. Of the 57 isolates tested in detail, 7 grew microcolonies, of which 2 (0.3% of all isolates tested) had confirmed microcolonies on repeat testing (6 tests performed, and microcolonies were present on at least 4). Both M. tuberculosis isolates were ofloxacin-resistant on screening, and had ofloxacin minimum inhibitory concentration (MIC) >8?μg/mL. The five other isolates were ofloxacin-susceptible on screening, but had regular colony growth (i.e., resistance) at the drug concentration that initially resulted in microcolonies (ofloxacin 0.5 or 1.0?μg/mL). Microcolonies were observed infrequently with fluoroquinolone susceptibility testing, but when confirmed, they were associated with drug resistance.     

Current interest of isoniazid in the chemotherapy of tuberculosis in the light of its in vitro activity

Isoniazid is one of the most useful drugs for the treatment of tuberculosis. However, in the last few years treatment with this drug has become long, complicated, and occasionally inefficient because of the increasing number of cases with resistance. The aim of our work was to know the isoniazid resistance level of 1,496 Mycobacterium tuberculosis strains that were submitted to the Mycobacteria Reference Center, Córdoba, during the years 1993-2000. A total of 1,186 strains were from pulmonary sources and 196 from extrapulmonary sources; no source was provided for 114 strains. All M. tuberculosis strains were previously identified by different methods. For sensitivity testing, the BACTEC 460 TB system was used initially and then the ESP II system was also used. The control strains used in this study were ATCC27294 (sensitive to SM, RP, EB, and INH) and ATCC35822, resistant to INH. The overall resistance rate obtained was 14.8%, of which 2.3% and 1.4% accounted for primary and secondary resistance types, respectively. Ninety-six out of the 221 resistant strains were resistant to INH only, and 8 strains were resistant to INH plus SM. A total of 117 multiresistant strains were found. An apparent increase in the resistance rate to INH in the last few years was observed. Secondary resistance has decreased, whereas primary resistance has increased. A continuous surveillance of resistance is required and, therefore, any patient with tuberculosis should undergo sensitivity testing to confirm therapy to be used.     

Antimicrobial susceptibility testing for Mycobacterium tuberculosis by the bioluminescence assay of mycobacterial ATP using filamentous cell treatment

The antimicrobial susceptibility testing for Mycobacterium tuberculosis by the bioluminescence assay of adenosine triphosphate(ATP) derived from living mycobacteria was improved introducing filamentous cell treatment(FCT) reported for beta-lactam susceptibility test of Pseudomonas aeruginosa by Hattori. Before ATP extraction, bacterial cells were treated with the FCT reagent for 30 minutes at room temperature. Adenosine phosphate deaminase in the FCT reagent simultaneously digested the extracted ATP and released ATP in a liquid culture of M. tuberculosis H37Rv and the RLU level was decreased markedly. Using this improved ATP method, we determined the ATP contents of M. tuberculosis inoculated into Middle-brook 7H9 broth medium with or without drugs. In ethambutol(EB) susceptibility, the ATP method reported previously, showed false-resistance when judged within 7 days. To eliminate false-resistance in EB susceptibility we applied the modified ATP method with FCT treatment to strains determined EB susceptible by reference methods. Using this modified ATP method, we could judge EB susceptibility of 5 ATCC reference strains within 3 days, and these of 15 clinical isolates of M. tuberculosis within 5 days. And all the results obtained were coincident between the ATP method and the reference methods. The reproducibility of this modified ATP method was evaluated with six ATCC reference strains at the concentrations of 0.1 microgram/ml of isoniazid(INH), 2.0 micrograms/ml of rifampicin(RFP), 2.5 micrograms/ml of EB, 2.0 micrograms/ml of streptomycin(SM), and 5.0 micrograms/ml of kanamycin(KM). The test was repeated six times. Reduction of ATP contents were observed in susceptible strains but not in resistant ones within 3 days of cultivation and susceptibilities to drugs could be determined within 3 days at every time when combined FCT to the ATP method. And highly reproducible results were obtained. It is strongly suggested that this modified method is simple, rapid, highly reproducible and nonradiometric, and could be used for the assessment of drug susceptibility for M. tuberculosis.     

Evaluation of BACTEC Mycobacteria Growth Indicator Tube (MGIT 960) Automated System for Drug Susceptibility Testing of Mycobacterium tuberculosis

The reliability of the BACTEC MGIT 960 system, an automated version of the Mycobacteria Growth Indicator Tube (MGIT), for antimicrobial susceptibility testing of Mycobacterium tuberculosis was evaluated on 78 clinical isolates. Rifampin (RMP), isoniazid (INH), streptomycin (SM), and ethambutol (EMB) were tested at the following concentrations: 1.0 microg/ml for RMP, 0.1 and 0.4 microg/ml for INH, 1.0 and 4.0 microg/ml for SM, and 5.0 and 7.5 microg/ml for EMB. Results were compared with those obtained by the BACTEC 460 TB radiometric system. Initially the reproducibility study showed 99.5% agreement on repeat testing with all the four drugs. With susceptibility testing of clinical isolates, excellent agreement between the two systems was found for all the drugs. A total of nine major errors were observed for only three isolates, resistant according to BACTEC MGIT 960 and susceptible according to BACTEC 460 TB, to SM (4.0 microg/ml), INH (0.1 microg/ml), and EMB (5.0 microg/ml) (one isolate) and to SM (1.0 microg/ml), INH (0.4 microg/ml), and EMB (5.0 microg/ml) (two isolates). When these isolates were tested by using the conventional proportion method on L?wenstein-Jensen medium, agreement with BACTEC MGIT 960 was found for five results and with BACTEC 460 TB for the remainder. The time to report results was 7.9 days by MGIT 960 and 7.3 days by BACTEC 460 TB, which was not found statistically significant (P > 0.05). In conclusion, the performance of BACTEC MGIT 960 was found similar to that of BACTEC 460 TB and this new system can be considered a good alternative to the radiometric method for routine susceptibility testing of M. tuberculosis.     

Biological and molecular characteristics of Mycobacterium tuberculosis clinical isolates with low-level resistance to isoniazid in Japan

We reevaluated the BACTEC MGIT 960 antimicrobial susceptibility testing system (MGIT 960 AST) by using 1,112 isolates of Mycobacterium tuberculosis. When the results of MGIT 960 AST were compared with that of the proportion method using Ogawa medium (Ogawa PM), discrepant results were obtained for 30 strains with isoniazid, all resistant by MGIT 960 AST but susceptible by Ogawa PM. For 93% of the strains that produced discrepant results, the MIC was 0.4 or 0.8 microg/ml, showing resistance by the proportion method using Middlebrook agar plates. Furthermore, it was also established by analyses of the katG and inhA genes that strains resistant only by MGIT 960 AST have a low level of isoniazid (INH) resistance, indicating that MGIT 960 AST is a reliable method. Ninety-six strains were resistant to 0.1 microg/ml INH by MGIT 960 AST. When they were divided into three groups, Low-S (susceptible at 0.2 microg/ml), Low-R (resistant at 0.2 microg/ml), and High-R (resistant at 1.0 microg/ml), by Ogawa PM, 43.3% of the Low-S strains had mutations in the promoter region of inhA and no mutations were detected in katG codon 315, while 61.7% of the High-R strains had katG codon 315 mutations or a gross deletion of katG. These results suggest that mutations in inhA are associated with low-level resistance to INH and katG codon 315 mutations are associated with high-level resistance to INH. In addition, the analyses demonstrated some relationship of mutations in the inhA gene with ethionamide resistance for the Low-S strains, but not for the High-R strains.