Permanently densified SiO2 glasses: a structural approach.

Densified silica can be obtained by different pressure and temperature paths and for different stress conditions, hydrostatic or including shear. The density is usually the macroscopic parameter used to characterize the different compressed silica samples. The aim of our present study is to compare structural modifications for silica glass, densified from several routes. For this, densified silica glasses are prepared from cold and high temperature (up to 1020 °C) compressions. The different densified glasses obtained in our study are characterized by micro-Raman spectroscopy. Intertetrahedral angles from the main band relative to the bending mode decrease and their values are larger for densified samples from high temperature compression than those samples from cold compression. The relative amount of 3-membered rings deduced from the D2 line area increases as a function of density for cold compression. The temperature increase during the compression process induces a decrease of the 3 fold ring population. Moreover, 3 fold rings are more deformed and stressed for densified samples at room temperature at the expense of those densified at high temperature. Temperature plays a main role in the reorganization structure during the densification and leads to obtaining a more relaxed structure with lower stresses than glasses densified from cold compression. The role of hydrostatic or non-hydrostatic applied stresses on the glass structure is discussed. From the Sen and Thorpe central force model, intertetrahedral angle average value and their distribution are estimated.

Permanent densification of compressed silica glass: a Raman-density calibration curve.

Raman scattering experiments have been carried out to study persistent densification in SiO(2) glass following hydrostatic compression at room temperature. A new relationship linking selective Raman parameters to the degree of densification in the glass has been developed here. This approach will allow quantification of the residual densification in silica following microindentation experiments, with the goal being the development of a constitutive law for amorphous silica.

[Evaluation of a colorimetric micromethod for determining the minimal inhibitory concentration of antibiotics against Mycobacterium tuberculosis]. / Evaluación de un micrométodo colorimétrico para determinar la concentración inhibitoria mínima de drogas antituberculosas frente a Mycobacterium tuberculosis.

Multidrug-resistant tuberculosis (MDR) caused by strains resistant to both isoniazid and rifampin is now considered a serious sanitary problem worldwide. New technical tools for the early detection of these strains are urgently needed to avoid their spread within the community. We have evaluated a microplate colorimetric-based method to determine the minimal inhibitory concentration (MIC) of first-line antituberculosis drugs by using 3-(4, 5 dimethylthiazolyl 1-2 yl)-2,5 diphenyl tetrazolium bromide as a bacterial growth indicator (MTT) (M-MTT). A total of 603 clinical isolates, 507 from respiratory cases (84.1%) and 96 from non-respiratory cases (15.9%) were processed. The proportion method on a Löwenstein-Jensen medium (PM) with isoniazid (INH), 0.20 microg/ml; streptomycin (SM), 4.00 microg/ml; ethambutol (EMB), 2.00 microg/ml and rifampin (RMP), 40.00 microg/ml, was used as the gold standard. The drugs and the concentration range tested were: INH, 1.00-0.03 microg/ml; SM, 8.00-0.25 microg/ml; EMB, 32.00-1.00 microg/ml and RMP, 2.00-0.06 microg/ml. MIC results were obtained on an average of 8 days (range: 7-12). The cut-off values for each drug, calculated by the ROC curve method, were: INH, 0.25 microg/ml, RMP, 0.50 microg/ml, SM, 4.00 microg/ml and EMB, 4.00 microg/ml. Sensitivity and specificity for RMP were 100 %, while for INH, they were 97.8% and 99.5% respectively. The results obtained suggested that M-MTT is a low cost and easy to set up method that could be applied to MDR clinical diagnosis in developing countries.

Evaluación de un micrométodo colorimétrico para determinar la concentración inhibitoria mínima de drogas antituberculosas frente a Mycobacterium tuberculosis / Evaluation of a colorimetric micromethod for determining the minimal inhibitory concentration of antibiotics against Mycobacterium tuberculosis

La tuberculosis multidrogorresistente (MDR), originada por aislamientos de cepas simultáneamente resistentes a isoniacida y rifampicina, es reconocida en la actualidad como un problema sanitario mundial. Nuevas técnicas que permitan detectar en forma temprana cepas MDR son necesarias para evitar su dispersión en la comunidad. En este trabajo hemos evaluado el empleo de un micrométodo colorimétrico para determinar las concentraciones inhibitorias mínimas (CIM) de las drogas de primera línea frente a dichas cepas, usando el indicador: bromuro de 3-(4,5 dimetiltiazol-2-yl)-2,5 difeniltetrazolio (M-MTT). Junto a la cepa de referencia H37Rv se procesaron 603 aislamientos clínicos, 507 provenientes de casos pulmonares (84,1%) y 96 de extrapulmonares (15,9%). Como estándar de referencia se utilizó el método de proporciones en medio de Löwenstein-Jensen (MP), con isoniacida (INH), 0,20 µg/ml; estreptomicina (SM), 4,00 µg/ml; etambutol (EMB), 2,00 µg/ml y rifampicina (RMP), 40,00 µg/ml. Los intervalos de concentraciones de las drogas empleadas en el M-MTT fueron: INH, 1,00-0,03 µg/ml; SM, 8,00-0,25 µg/ml; EMB, 32,00-1,00 µg/ml y RMP: 2,00-0,06 µg/ml. El resultado de la CIM por el M-MTT fue obtenido en un tiempo promedio de 8 días (rango total: 7 a 12 días). Los puntos de corte para cada una de las drogas, calculados mediante el análisis de la curva ROC, fueron: INH, 0,25 µg/ml; RMP, 0,50 µg/ml; SM, 4,00 µg/ml y EMB, 4,00 µg/ml. Los valores de sensibilidad y especificidad fueron 100% en el caso de RMP; y 97,8% y 99,5%, respectivamente, para INH. El análisis estadístico de los resultados permitió concluir que el M-MTT es un método seguro para la rápida detección de MDR. Por su sencillez y bajo costo, podría ser aplicado en los países en vías de desarrollo.

Multidrug-resistant tuberculosis (MDR) caused by strains resistant to both isoniazid and rifampin is now considered a serious sanitary problem worldwide. New technical tools for the early detection of these strains are urgently needed to avoid their spread within the community. We have evaluated a microplate colorimetric-based method to determine the minimal inhibitory concentration (MIC) of first-line antituberculosis drugs by using 3-(4, 5 dimethylthiazolyl 1-2 yl)-2,5 diphenyl tetrazolium bromide as a bacterial growth indicator (MTT) (M-MTT). A total of 603 clinical isolates, 507 from respiratory cases (84.1%) and 96 from non-respiratory cases (15.9%) were processed. The proportion method on a Löwenstein-Jensen medium (PM) with isoniazid (INH), 0.20 µg/ml; streptomycin (SM), 4.00 µg/ml; ethambutol (EMB), 2.00 µg/ml and rifampin (RMP), 40.00 µg/ml, was used as the gold standard. The drugs and the concentration range tested were: INH, 1.00-0.03 µg/ml; SM, 8.00-0.25 µg/ml; EMB, 32.00-1.00 µg/ml and RMP, 2.00-0.06 µg/ml. MIC results were obtained on an average of 8 days (range: 7-12). The cut-off values for each drug, calculated by the ROC curve method, were: INH, 0.25 µg/ml, RMP, 0.50µg/ml, SM, 4.00 µg/ml and EMB, 4.00 µg/ml. Sensitivity and specificity for RMP were 100 %, while for INH, they were 97.8% and 99.5% respectively. The results obtained suggested that M-MTT is a low cost and easy to set up method that could be applied to MDR clinical diagnosis in developing countries.

Evaluation of a rapid culture method for tuberculosis diagnosis: a Latin American multi-center study.

SETTINGS: Tuberculosis (TB) diagnostic laboratories in Latin America. OBJECTIVES: Evaluation of thin-layer agar (TLA) compared to Löwenstein-Jensen (LJ) culture for the diagnosis of TB. DESIGN: Phase II prospective study in six laboratories. Samples included sputum and extra-pulmonary specimens from patients with a clinical diagnosis of TB. Respiratory samples were decontaminated using NaOH/ NALC; all samples were centrifuged, stained with Ziehl-Neelsen for acid-fast bacilli (AFB), cultured on LJ and TLA and identified according to recommended procedures. Sensitivity and likelihood ratios (LR), growth detection time and contamination rate were calculated for both media. RESULTS: A total of 1118 clinical specimens were studied. Cultures detected Mycobacterium tuberculosis in all AFB-positive samples, whereas for AFB-negative specimens LJ detected 3.2% and TLA 4.4%. Sensitivity was 92.6% (95%CI 87.9-95.9) and 84.7% (95%CI 78.8-89.0) for TLA and LJ, respectively. Positive and negative LRs were similar. Contamination was 5.1% for TLA and 3.0% for LJ. Median time to detection of a positive culture was 11.5 days (95%CI 9.3-15.0) for TLA and 30.5 days (95%CI 26.9-39.0) for LJ (P < 0.0001). CONCLUSION: Difference in the characteristics of the participating laboratories, the disease prevalence and the number and type of specimens processed did not affect the overall performance of TLA as compared to LJ, supporting the robustness of the method and its feasibility in different laboratory settings.