吡嗪酰胺耐药性结核分枝杆菌的噬菌体检测技术研究

目的 建立噬菌体生物扩增法（PhaB）快速测定吡嗪酰胺耐药性，并探讨其在结核分枝杆菌吡嗪酰胺耐药性测定中的应用价值。方法 应用建立的PhaB测定108株结核分枝杆菌临床分离株的吡嗪酰胺耐药性，并与绝对浓度法的药敏结果进行比较，对不符合的菌株进行最低抑菌浓度（MIC）测定和序列测定分析。结果 PhaB检测吡嗪酰胺耐药性的最佳测定条件为pH值5．5、药物浓度200μg／ml、37℃作用48h。用绝对浓度法检测108株结核分枝杆菌临床分离株，其中吡嗪酰胺敏感33株、耐药75株；用PhaB检测该108株结核分枝杆菌临床分离株，若以噬菌斑减少95％为判断标准。则吡嗪酰胺敏感32株，耐药76株。2种方法检测均为敏感的为28株，均为耐药的为71株，符合率为91．7％；2种方法检测结果不符的为9株，其中5株的PhaB结果与MIC结果相符，4株的结果不符，测序结果表明9株中有7株的PhaB结果与测序结果相符。如以绝对浓度法药敏结果为判断标准，PhaB检测吡嗪酰胺耐药性的敏感性为94．7％，特异性为84．8％，阳性预测值为93．4％，阴性预测值为87．5％，准确性为91．7％。结论 PhaB测定吡嗪酰胺耐药性简便、快速，3d即可获得药敏结果，可作为吡嗪酰胺耐药性的快速筛选方法。     

吡嗪酰胺致皮肤色素沉着症135例临床报告

目的系统观察吡嗪酰胺的副反应。方法对初治结核（肺结核、骨关节结核等肺外结核）给予6HR（D）Z／3HR（D）、肺外结核9HR（D）Z／7HR（D）治疗。即异烟肼（H）0．3g，利福平（R）0．45g、利福定（D）0．6g、吡嗪酰胺（z）1．50g，每日早晨一次空腹服用，过一个半小时后方可进食。结果出现局限性、暂短性、光感性皮肤色素沉着症135例，占3．5％（135／3756）。结论吡嗪酰胺为抗结核重要组成部分，观察其皮肤色素反应135例发生率为3．5％，停药后在2个月内自然消退，不需治疗，不留疤痕。     

结核分枝杆菌吡嗪酰胺耐药相关蛋白的原核表达及纯化

目的构建结核分枝杆菌pncA基因的原核表达质粒,获得结核分枝杆菌吡嗪酰胺酶的表达蛋白。方法制备结核分枝杆菌基因组DNA,采用聚合酶链反应扩增目的基因片段;通过pET28a构建表达载体pET28a-pncA,序列测定证实正确后转化大肠埃希菌DH10b,经IPTG诱导表达His-吡嗪酰胺酶融合蛋白,采用SDS-PAGE和Western blot分析重组蛋白。结果扩增出结核分枝杆菌pncA基因并构建了具有正确基因序列的质粒载体pET28a-pncA,转化大肠埃希菌BL21后经诱导产生了分子质量单位约20ku的表达产物,并得到纯化的带His标签的目的蛋白。结论构建了结核分枝杆菌pncA基因原核表达质粒,并诱导表达了His-吡嗪酰胺酶融合蛋白,为进一步研究吡嗪酰胺耐药性奠定了基础。     

10-23脱氧核酶对结核分枝杆菌异柠檬酸裂合酶表达的影响及其抗菌作用

目的探讨10-23脱氧核酶(deoxyribozyme,DRZ)抑制结核分枝杆菌异柠檬酸裂合酶(isocitrate lyase,ICL)的表达及其在抗结核分枝杆菌感染中的作用。方法根据计算机模拟的结核分枝杆菌ICL mRNA的二级结构设计合成5条ICL特异的10-23 DRZ(DZ1～DZ5),在无细胞反应体系中鉴定其对结核分枝杆菌ICL mRNA的切割活性后,在不同条件下用DZ4对结核分枝杆菌进行处理,于处理后不同时间检测ICL酶活性变化,间接酶联免疫吸附测定法(ELISA)检测ICL的表达。用异烟肼单独处理及DZ4与异烟肼联合处理后的结核分枝杆菌感染人巨噬细胞系THP-1细胞,于感染后不同时间用Ziehl-Heelson染色法和结核分枝杆菌培养计数的方法,观察10-23DRZ对结核分枝杆菌感染巨噬细胞的影响,同时取经异烟肼单独处理及DZA与异烟肼联合处理后的结核分枝杆菌接种于Middle Brook 7H10(M7H10)培养基,观察10-23DRZ对在巨噬细胞外生长的结核分枝杆菌的影响。结果DZ1、DZ3、DZ4和DZ5在无细胞反应体系中可对ICL mRNA进行有效切割,且其活性具有高度特异性。5μmol／L DZ4与异烟肼联合应用时可显著抑制结核分枝杆菌ICL的表达,与单用相应浓度的异烟肼比较,处理1、2、3周后结核分枝杆菌ICL酶活性分别下降34．9％、46．6％、46．7％(异烟肼10μg／L)或21．9％、33．48、36．9％(异烟肼5μg/L)。DZ4与异烟肼联合处理后的结核分枝杆菌在巨噬细胞内存活的能力显著下降,在感染后4 d和7 d时,THP-1细胞内的荷菌量分别由单用相应浓度异烟肼处理对照组的126．5×104 CFU、307．5×104 CFU(异烟肼10μg／L)和133．0×104 CFU、325．4×104 CFU(异烟肼5μg／L)下降至54．6×104 CFU、114．3×104 CFU和71．7×104 CFU、174．4×104 CFU。10-23DRZ对结核分枝杆菌在M7H10培养基中生长无明显影响。结论异烟肼可有效促进10-23DRZ进入结核分枝杆菌;10-23DRZ与亚抑菌浓度的异烟肼联用可有效抑制结核分枝杆菌ICL的表达,降低其在巨噬细胞中的存活能力。     

以脂肪酸合成酶FabH为靶标的化合物体外抗结核作用的初步研究

目的研究结核分枝杆菌脂肪酸合成酶FabH为靶标的化合物的体外抗结核活性，研制新的高效、安全的抗结核药物。方法以平板滤纸法测定化合物对草分枝杆菌的抑菌圈，以试管抑菌法检测化合物对结核分枝杆菌药物敏感株和耐多药分离株的抑制作用。结果18种化合物在500μmol／L浓度时对草分枝杆菌的抑菌圈为1．8～2．4cm，其中7种化合物在250μmol／L和125μmol／L浓度时对草分枝杆菌的抑菌圈为1．5～2．2cm。结核分枝杆菌H37Rv标准株在分别含3mmol／L的18种化合物的培养基上培养2周时，绝大多数含化合物培养基上未见细菌生长；培养4周时，No．115、No．131、No．128、No．129、No．137化合物的抑菌作用较明显。结核分枝杆菌耐多药分离株HB240在分别含3mmol／L的11种化合物的培养基上培养2周和4周时，No．115化合物均显示明显的抑菌作用。结论以脂肪酸合成酶FabH为靶标的大多数化合物在体外都具有不同程度的抗结核活性，尤其是No．115化合物对草分枝杆菌、结核分枝杆菌敏感株和耐药株都具有明显的抑制作用。     

抗结核新药的研究进展

目前异烟肼、链霉素、利福平、吡嗪酰胺和乙胺丁醇是一线抗结核药物。但随着耐药结核菌的出现．特别是耐多药，严重影响结核病的控制。1980年一些新抗结核药物．如对氨基水杨酸-异烟肼(Dipasic，Pasiniazide，结核清、力排肺疾、力克菲蒺)．利福喷丁(环戊基利福霉素，DL473,迪克菲)，利福布丁(Ansamycin,LM427),氧氟沙星、左旋氧氟沙星、卷曲霉素、斯帕沙星等国内已有报告。现介绍一些近期的新药研究进展。     

结核分枝杆菌L型的诱导及其对抗菌药物的敏感性

目的：观察异烟肼、利福平、乙胺丁醇抗结核药物诱导形成结核分支杆菌L型以及结核分支杆菌L型对抗菌药物敏感性。方法将结核分支杆菌接种于含有不同质量浓度利福平（0．05、0．1、0．2μg/mL）、异烟肼（0．01、0．04、0．08μg/mL）、乙胺丁醇（1、2．5、5μg/mL）的BD960液体培养基内,10 d后在显微镜下观察结核分支杆菌L型的形成情况。培养结核分支杆菌L型,在显微镜高倍镜下观察,并检测其对抗菌药物的敏感性。结果0．1、0．2μg/mL利福平,0．04、0．08μg/mL异烟肼,2．5、5μg/mL乙胺丁醇可诱导形成结核分支杆菌L型。在含有4μg/mL链霉素、0．2μg/mL异烟肼、40μg/mL利福平、2μg/mL乙胺丁醇、1μg/mL对氨基水杨酸的非高渗培养基内培养7 d后均可见结核分枝杆菌L型生长,而含有30μg/mL卡那霉素、40μg/mL卷曲霉素、3μg/mL氧氟沙星的培养基内未见其生长。结论中高浓度的利福平、异烟肼、乙胺丁醇能够诱导结核分支杆菌L型形成。结核分枝杆菌L型对卡那霉素、卷曲霉素、氧氟沙星敏感。     

吡嗪酰胺对人体单核细胞培养分化的巨噬细胞内的结核分支杆菌无抗菌作用

地点:克罗拉多州,丹佛,国家犹太人医学和研究中心微生物学实验室。 目的:评价吡嗪酰胺对人体单核细胞培养分化的正常和激活的巨噬细胞中结核分支杆菌的抗菌作用。 设计:将人体血中分离的单核细胞在塑料平皿中培养7天使其衍化成巨噬细胞单层。使用TNF-α或IFN-γ激活或未经过处理的巨噬细胞感染结核分支杆菌。次日加入不同浓度的吡嗪酰胺(PZA)、吗啉酰胺(MZA)或异烟肼(INH),并于第0、4、8天记数细胞内的活菌数。 结果:不论其浓度大小均未发现吡嗪酰胺的抑菌作用,而在同一实验模型中则观察到了随着MZA和异烟肼剂量增加其抑菌和杀菌作用也增加。 结论:PZA对人体单核细胞培养分化的巨噬细胞内滞留或繁殖的结核分支杆菌既无抑菌作用又无杀菌作用,关于人们所知道的该药对结核病人的效力可能与所推测的该药对细胞内菌群的抗菌作用无关。     

反义寡脱氧核苷酸对耻垢分枝杆菌抑制作用的研究

目的研究反义寡脱氧核苷酸对耻垢分枝杆菌生长的抑制作用,探讨其潜在的抗结核作用。方法在7H9培养基中接种5×10^5耻垢分枝杆菌MC^2 155,同时加入20μmol／L针对结核分枝杆菌中必须基因RV3806c在耻垢分枝杆菌中的同源基因MSMEG_6401的反义寡脱氧核苷酸。以耻垢分枝杆菌MC^2 155单独培养作为对照。观察和绘制细菌生长曲线;测定细胞膜MSMEG_6401编码的磷酸核糖转移酶的生物活性;应用高压气相色谱测定耻垢分枝杆菌细胞壁中糖的含量。结果与对照组相比,试验组耻垢分枝杆菌增殖速度平均降低0.45 OD（P〈0.01）;CFU计数平均延缓0．67Log;在应用等量的膜蛋白的情况下,实验组磷酸核糖转移酶的生物活性降低约40％,试验组和对照组细菌反应细胞壁的糖含量的指标甘露糖-半乳糖,阿拉伯糖比率没有明显差异（2组实验组分别为63％和69．4％;2组对照组分别为66．6％和69．1％）。结论针对MSMEG_6401的反义寡脱氧核苷酸对耻垢分枝杆菌的增殖有一定程度的抑制作用,推测反义寡脱氧核苷酸技术有一定抗结核价值;结核分枝杆菌的RV3806c基因或者是其编码产物可能是一个好的抗结核药物作用靶位。     

DNA测序预测一线抗结核药物敏感性

<正>背景世界卫生组织建议对所有结核病患者进行结核分枝杆菌的药物敏感性试验,以指导治疗方案和提高疗效。DNA测序能否准确预测一线抗结核药物的敏感性尚不明确。方法本研究获得了6大洲16个国家的菌株对一线抗结核药物异烟肼、利福平、乙胺丁醇和吡嗪酰胺的耐药或敏感的全基因组序列和相关表型。对于每一株菌株,通过9个     

Pyrazinoic acid efflux rate in Mycobacterium tuberculosis is a better proxy of pyrazinamide resistance

Pyrazinamide is one of the most important drugs in the treatment of latent Mycobacterium tuberculosis infection. The emergence of strains resistant to pyrazinamide represents an important public health problem, as both first- and second-line treatment regimens include pyrazinamide. The accepted mechanism of action states that after the conversion of pyrazinamide into pyrazinoic acid by the bacterial pyrazinamidase enzyme, the drug is expelled from the bacteria by an efflux pump. The pyrazinoic acid is protonated in the extracellular environment and then re-enters the mycobacterium, releasing the proton and causing a lethal disruption of the membrane. Although it has been shown that mutations causing significant loss of pyrazinamidase activity significantly contribute to pyrazinamide resistance, the mechanism of resistance is not completely understood. The pyrazinoic acid efflux rate may depend on multiple factors, including pyrazinamidase activity, intracellular pyrazinamidase concentration, and the efficiency of the efflux pump. Whilst the importance of the pyrazinoic acid efflux rate to the susceptibility to pyrazinamide is recognized, its quantitative effect remains unknown. Thirty-four M.?tuberculosis clinical isolates and a Mycobacterium smegmatis strain (naturally resistant to PZA) were selected based on their susceptibility to pyrazinamide, as measured by Bactec 460TB and the Wayne method. For each isolate, the initial velocity at which pyrazinoic acid is released from the bacteria and the initial velocity at which pyrazinamide enters the bacteria were estimated. The data indicated that pyrazinoic acid efflux rates for pyrazinamide-susceptible M.?tuberculosis strains fell within a specific range, and M.?tuberculosis strains with a pyrazinoic acid efflux rate below this range appeared to be resistant. This finding contrasts with the high pyrazinoic acid efflux rate for M.?smegmatis, which is innately resistant to pyrazinamide: its pyrazinoic acid efflux rate was found to be 900 fold higher than the average efflux rate for M.?tuberculosis strains. No significant variability was observed in the pyrazinamide flux rate. The pyrazinoic acid efflux rate explained 61% of the variability in Bactec pyrazinamide susceptibility, 24% of Wayne activity, and 51% of the Bactec 460TB growth index. In contrast, pyrazinamidase activity accounted for only 27% of the Bactec pyrazinamide susceptibility. This finding suggests that mechanisms other than pncA mutations (reduction of pyrazinamidase activity) are also implicated in pyrazinamide resistance, and that pyrazinoic acid efflux rate acts as a better proxy for pyrazinamide resistance than the presence of pncA mutations. This is relevant to the design of molecular diagnostics for pyrazinamide susceptibility, which currently rely on pncA gene mutation detection.     

Pyrazinamide is not active against Mycobacterium tuberculosis residing in cultured human monocyte-derived macrophages.

SETTING: Mycobacteriology Laboratory, National Jewish Medical and Research Center, Denver, Colorado. OBJECTIVE: To evaluate the antimicrobial activity of pyrazinamide against Mycobacterium tuberculosis in cultured human monocyte-derived normal and activated macrophages. DESIGN: Monocytes separated from human blood were incubated in plastic plates for seven days to mature into macrophage monolayers. After activation with TNF-alpha or IFN-gamma or without prior treatment, the macrophages were infected with M. tuberculosis. Various concentrations of pyrazinamide (PZA), morphazinamide (MZA) or isoniazid (INH) were added the next day, and the viable counts of the intracellular bacteria were determined at days 0, 4, and 8. RESULTS: No inhibitory activity of PZA at any concentration was detected, while clear dose-dependent bacteriostatic and bactericidal activities were demonstrated by MZA and INH in the same experimental model. CONCLUSIONS: PZA has neither bacteriostatic nor bactericidal activity against M. tuberculosis persisting or multiplying in cultured monocyte-derived human macrophages, and it might be that the well-known effectiveness of this drug in tuberculosis patients is not related to its supposed activity against intracellular bacterial subpopulations.     

Frequency and implications of pyrazinamide resistance in managing previously treated tuberculosis patients.

OBJECTIVE: To determine the extent of pyrazinamide (PZA) resistance in isolates from previously treated patients from the Western Cape, South Africa. DESIGN: Drug-resistant isolates, isolates resistant to one or more drugs other than PZA (PZA resistance is not routinely determined) (n = 127), and drug-susceptible (n = 47) clinical isolates of Mycobacterium tuberculosis from previously treated patients from the Western Cape were phenotypically (BACTEC MGIT 960) and genotypically (pncA gene sequencing) analysed for PZA resistance. RESULTS: MGIT analysis found that 68 of the 127 drug-resistant isolates were PZA-resistant. Nearly all (63/68) PZA-resistant isolates had diverse nucleotide changes scattered throughout the pncA gene, and five PZA-resistant isolates had no pncA mutations. Of the 47 phenotypically susceptible isolates, 46 were susceptible to PZA, while one isolate was PZA-monoresistant (OR = 53.0, 95% CI = 7.1-396.5). A pncA polymorphism (Thr114Met) that did not confer PZA resistance was also identified. PZA resistance was strongly associated with multidrug-resistant tuberculosis (MDR-TB). CONCLUSION: An alarmingly high proportion of South African drug-resistant M. tuberculosis isolates are PZA-resistant, indicating that PZA should not be relied upon in managing patients with MDR-TB in the Western Cape. A method for the rapid detection of PZA resistance would be beneficial in managing patients with suspected drug resistance.     

The paradox of pyrazinamide: an update on the molecular mechanisms of pyrazinamide resistance in Mycobacteria

Pyrazinamide (PZA) is an important front line anti-tuberculosis drug because of its sterilizing activity against semi-dormant tubercle bacilli. In spite of its remarkable role in shortening the treatment duration from 9 months to 6 months when used in combination with Rifampicin and Isoniazid, PZA remains a difficult paradox because of its incompletely understood mode of action and mechanism of resistance. PZA is a nicotinamide analog prodrug which is converted into the active bactericidal form pyrazinoic acid by the bacterial enzyme pyrazinamidase (PZase). PZA does not appear to have a specific cellular target and instead, exerts its bactericidal effect by disrupting the membrane energetics and acidification of cytoplasm. Majority (72-97%) of PZA-resistant isolates of M. tuberculosis exhibit mutations in their pncA gene or upstream area leading to loss of PZase activity. A wide diversity of pncA mutations scattered along the entire length of pncA gene is unique to PZA resistance. However, PZA resistant isolates with normal PZase activity and wild type pncA sequences have also been reported in several studies which indicate that alternate mechanisms of PZA resistance exist. Investigations into these mechanisms would be useful in developing alternative diagnostic/therapeutic measures. This review presents the update of various mechanisms of PZA resistance in different mycobacteria with special emphasis on mode of action of PZA and mechanisms of resistance in Mycobacterium tuberculosis.     

Characterisation of the pncA gene in Mycobacterium tuberculosis isolates from Gauteng, South Africa.

SETTING: The use of pyrazinamide (PZA) is important for the treatment of Mycobacterium tuberculosis as it is bactericidal to semi-dormant mycobacteria that are not affected by other drugs. The incidence of resistance to PZA and other drugs used in the treatment of M. tuberculosis is increasing in South Africa. OBJECTIVE: To characterise the pncA gene of M. tuberculosis isolates from Gauteng, South Africa, and to develop a rapid diagnostic method. DESIGN: The pncA gene and the putative regulatory gene were characterised by sequence analysis in a total of six PZA susceptible and 15 resistant isolates. The association with classical PZA susceptibility testing and PZase activity was determined. RESULTS: All PZA-resistant isolates were PZase negative as well as resistant to at least one other anti-tuberculosis drugs. Mutations were identified throughout the length of the pncA gene in 10/15 PZA-resistant isolates. Five lacked PZase activity, but the wild type pncA sequence was present. In all six PZase-positive strains, a PZA-susceptible pattern was obtained on BACTEC and the wild type pncA sequence was present. CONCLUSION: Sequencing is an effective means to identify mutations in the pncA gene in M. tuberculosis and therefore resistance to PZA. The fact that some PZA-resistant M. tuberculosis isolates lack mutations in the pncA gene suggests that alternative mechanisms for drug resistance exist. In PZase negative strains with no genetic changes which are resistant to 100 microg/ml and susceptible to 300 microg/ml, 300 microg/ml may be a more reliable breakpoint.     

Chemotherapy of tuberculosis in mice using single implants of isoniazid and pyrazinamide.

OBJECTIVE: To establish the chemotherapeutic value of a depot drug preparation of isoniazid and pyrazinamide against experimental tuberculosis. DESIGN: To see whether sustained levels of pyrazinamide are available for prolonged periods after a single subcutaneous administration of a biodegradable polylactic-glycolic acid (PLGA) polymer containing the drug, studies were done to ascertain whether a single administration of isoniazid and pyrazinamide in separate PLGA polymers could offer chemotherapeutic protection against a heavy intravenous challenge of susceptible mice with a virulent strain of Mycobacterium tuberculosis similar to that rendered by daily administration of the two drugs for 8 weeks. RESULTS: Even with three times the daily dose of pyrazinamide contained in the single PLGA polymer implant, no abnormally high (burst) levels of the drug were evident after administration, but sustained levels of the drug were seen up to 54 days. The chemotherapeutic activity of the single PLGA polymer implants was similar to that obtained with standard oral treatment with the two drugs given daily for the entire 8 weeks, as judged by mortality and colony forming unit (CFU) counts of tubercle bacilli from lungs and spleen. CONCLUSION: Treatment with single implants of the PLGA polymer containing anti-mycobacterial drugs offers a strong possibility of circumventing the compliance problem.     

颗粒显色指示技术快速检测结核分枝杆菌对吡嗪酰胺耐药性的价值

目的 探讨颗粒显色指示技术快速测定结核分枝杆菌（Mycobacterium tuberculosis,Mtb）对吡嗪酰胺耐药性的临床应用价值。方法 应用颗粒显色指示法测定102株Mtb对吡嗪酰胺耐药性,并与美国BD公司BACTEC MGIT-960分枝杆菌检测系统结果进行比较。 结果 颗粒显色指示法测定102株Mtb临床分离株,结果对吡嗪酰胺敏感70株、耐药32株,BACTEC MGIT-960法测定结果敏感69株、耐药33株;两法测定均敏感67株、均耐药30株。如以BACTEC MGIT-960法药敏结果为判断标准,则颗粒显色指示法测定吡嗪酰胺耐药性的敏感度为90.9%(30/33),特异度为97.1%（67/69),阳性预测值为93.8%(30/32),阴性预测值为95.7%(67/70),准确性为95.1%(97/102)。结论 颗粒显色指示技术快速测定Mtb吡嗪酰胺耐药性简便快速,操作不需特殊仪器设备,具有很高的临床应用价值。     

Absence of the genetic marker IS6110 from a strain of Mycobacterium tuberculosis isolated in Ontario

A 35-year-old female patient from Waterloo, Ontario was diagnosed with pulmonary tuberculosis in June 1995. Records indicated that the patient had emigrated from Laos circa 1990. A culture grown from a bronchoalveolar lavage specimen was identified as Mycobacterium tuberculosis by standard biochemical methods. Drug-susceptibility testing indicated the strain was resistant to pyrazinamide (PZA), and a mutation was detected within pncA, a gene associated with PZA resistance. Sequence data from the 16S rRNA gene and the 16S/23S rRNA gene spacer confirmed that the strain was a member of the M tuberculosis complex, and analysis of the mpcA and pncA genes supported the identification of the strain as M tuberculosis rather than Mycobacterium bovis. However, the insertion element IS6110, which is used for epidemiological tracing of M tuberculosis, was not detected in this strain by either restriction fragment length polymorphism analysis or by polymerase chain reaction. Two other genetic markers associated with the M tuberculosis complex, IS1081 and the direct repeat element, were present. The arrival of immigrants with tuberculosis from southeast Asia, where most strains of M tuberculosis lacking IS6110 have been traced, has important implications for epidemiological studies of tuberculosis in North America.     

Characterization of pyrazinamide and ofloxacin resistance among drug resistant Mycobacterium tuberculosis isolates from Singapore.

OBJECTIVES: To evaluate rapid molecular approaches for the detection of pyrazinamide (PZA) and ofloxacin resistance, by screening 100 known drug-resistant Mycobacterium tuberculosis isolates. METHODS: Mycobacterium tuberculosis isolates were tested for phenotypic resistance to pyrazinamide and ofloxacin using the BACTEC 460 radiometric method and the E-test, respectively. Mutation screening was done by amplifying the pncA, gyrA, and gyrB genes by the polymerase chain reaction (PCR) and direct automated sequencing. RESULTS: Twelve isolates were PZA-resistant and 8 of 12 (66.7%) isolates had missense mutations or deletions at the pncA gene, suggesting that mutation or deletion at the pncA gene is the major molecular mechanism of PZA resistance among the Singaporean isolates. Using the E-test, 48 isolates were resistant to ofloxacin, with minimum inhibitory concentrations of 4 microg/mL or higher. No mutations were observed at the quinolone resistance-determining region (QRDR) of gyrA in all isolates. At the QRDR of gyrB, mutations were present in 1 of 48 ofloxacin-resistant isolates and 0 of 19 ofloxacin-susceptible isolates. CONCLUSIONS: In Singapore, genotypic analysis of resistance to PZA and ofloxacin is inadequate and should be complemented by conventional methods.