Performance of Xpert MTB/RIF for detection of Mycobacterium tuberculosis and rifampicin resistance in pus aspirates.

INTRODUCTION: WHO endorsed Xpert MTB/RIF assay has proven to be rapid with results obtained within 2h. The evidence base regarding the use of Xpert MTB/RIF in pulmonary TB is strong. Relatively few performance data have been published to date on detection of Mycobacterium tuberculosis in aspirated pus specimens from abscesses. OBJECTIVES: The aim of the study was to determine the sensitivity and specificity of Xpert MTB/RIF assay for the detection of M. tuberculosis and rifampicin resistance in aspirated pus specimens using culture on Lowenstein Jensen (LJ) medium and economic variant of proportion method (PM) for drug susceptibility testing (DST) as the reference standard. RESULTS: Xpert MTB/RIF assay in comparison to conventional reference method showed sensitivity and specificity of 76.19% and 68.75% for detection of M. tuberculosis and 71.4% and 100% for detection of rifampicin resistance respectively. CONCLUSION: The simplicity, sensitivity, speed and automation makes this assay a very promising diagnostic test for detection of M. tuberculosis and rifampicin resistance in aspirated pus specimens.

Diagnostic accuracy of Xpert MTB/RIF assay in extrapulmonary tuberculosis.

INTRODUCTION: The WHO endorsed Xpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) assay, has been evaluated for pulmonary TB in a number of studies but very few have investigated it for extrapulmonary specimens. The present study evaluates the performance of Xpert MTB/RIF assay in the diagnosis of extrapulmonary TB (EPTB). AIM AND OBJECTIVES: The aim of the study is to determine sensitivity and specificity of Xpert MTB/RIF assay for diagnosis of EPTB and RIF resistance in comparison to culture on Lowenstein-Jensen (LJ) medium and proportion method (PM), respectively. MATERIALS AND METHODS: A total of 738 specimens from clinically suspected cases of EPTB were subjected to Ziehl-Neelsen staining, Xpert MTB/RIF assay and culture on LJ medium. PM was done on MTB isolates. RESULTS: The sensitivity, specificity of Xpert MTB/RIF assay for diagnosis of EPTB were 84.91% (95% confidence interval [CI] 72.41%-93.25%) and 86.72% (95% CI 83.94%-89.17%) and for RIF resistance detection were 60.00% (95% CI 32.29%-83.66%) and 94.74% (95% CI 73.97%-99.87%), respectively. Among culture-positive cases, the sensitivity of Xpert MTB/RIF assay was 94.12% in smear positive and 80.56% in smear-negative cases. Xpert MTB/RIF showed maximum sensitivity of MTB detection from lymph node specimens (100% [95% CI 54.07%-100.00%]) and other body fluids (100% [95% CI 15.81%-100.00%]). CONCLUSION: The present study establishes Xpert MTB/RIF assay as a promising tool in the rapid diagnosis of EPTB and detection of RIF resistance.

Concurrent evaluation of microscopic observation of drug susceptibility assay for pulmonary and extrapulmonary tuberculosis.

BACKGROUND: Methods for detection and drug susceptibility of tuberculosis (TB) with solid media are inexpensive but slow and laborious. Rapid methods to diagnose TB and multidrug-resistant TB (MDR-TB) are a global priority for TB control. OBJECTIVES: A study was performed to compare the sensitivity of detection of mycobacterial growth and time of culture positivity by microscopic observation of drug susceptibility (MODS) assay with that of Lowenstein-Jensen (LJ) culture in pulmonary and extrapulmonary TB and to evaluate the concordance of the susceptibilities to isoniazid (INH) and rifampicin (RIF) by MODS and proportion method on LJ. MATERIALS AND METHODS: A prospective, laboratory-based study was conducted on a total of 300 samples from suspected cases of pulmonary and extrapulmonary TB. Samples were inoculated on LJ medium as per the standard guidelines and MODS assay was performed. RESULTS: Sensitivity of MODS assay was 80% and 83.3% and specificity was 92.9% and 83.3% for pulmonary and extrapulmonary samples, respectively. Difference between mean time to detection of Mycobacterium TB (MTB) by LJ medium and MODS was statistically significant, with MODS being faster. drug susceptibility testing (DST) by MODS when compared to economic variant of proportion method was 87.87% for RIF, 90.9% for INH, and 96.96% for MDR-TB detection. CONCLUSION: MODS assay provides rapid, safe, and sensitive detection of TB faster than the existing gold standard. It is extremely promising in effectively diagnosing MDR-TB.

Detection of ofloxacin resistance by nitrate reductase assay in Mycobacterium tuberculosis isolates from extrapulmonary tuberculosis.

CONTEXT: Increased use of fluoroquinolones to treat community-acquired infections has led to the decreased susceptibility to Mycobacterium tuberculosis. There is a paucity of data on ofloxacin (OFX) resistance detection by nitrate reductase assay (NRA). Hence, the present study was carried out to find the efficacy of NRA for detection of OFX resistance in M. tuberculosis isolated from extrapulmonary tuberculosis (EPTB) cases. AIMS: (1) To compare sensitivity, specificity and median time required to obtain results by NRA with economic variant proportion method (PM) for detection of OFX resistance.(2) To determine the extent of OFX resistance in clinical isolates of M. tuberculosis. SETTINGS AND DESIGN: Seventy-three M. tuberculosis isolates from cases of EPTB were subjected to economic variant of PM for isoniazid, rifampicin and OFX. NRA was done for detection of OFX resistance. SUBJECTS AND METHODS: Seventy-three isolates from clinical samples of suspected EPTB received in the Department of Microbiology were included in the study. Drug susceptibility test was performed on Lowenstein-Jensen medium with and without drugs. STATISTICAL ANALYSIS USED: Of turnaround time was done by Mann-Whitney test on SPSS (version 19, released in 2010, IBM Corp, Armonk NY),P < 0.05. RESULTS: OFX resistance was seen in nine isolates. The sensitivity and specificity of OFX resistance by NRA was 100% and 96.87%, respectively. Median time required to obtain results by NRA was 10 days as compared to 28 days by PM. CONCLUSIONS: NRA is a specific and sensitive method for detection of OFX resistance in resource-restricted settings.

Drug susceptibility testing of rapidly growing mycobacteria in extrapulmonary tuberculosis.

There has been an increasing awareness of the rapidly growing mycobacteria (RGM), of which numerous species and phylogenetic groups are clearly established human pathogens. It is important to appropriately distinguish RGM from other mycobacteria, as first-line antituberculous drugs are ineffective for their treatment. Variability in susceptibility of RGM is seen in relation to species, different geographical areas, and time. Therefore, we conducted a study to speciate the isolates of RGM and perform antimicrobial susceptibility testing. The study was carried out in the department of microbiology of a tertiary care hospital. This study included 40 isolates of RGM obtained from clinical specimens from suspected cases of extrapulmonary tuberculosis. Forty isolates of RGM were speciated by phenotypic methods and drug susceptibility testing was done by broth microdilution method. Of the 40 isolates of RGM, 55% belonged to Mycobacterium fortuitum group, 35% were M. smegmatis group, and 10% were M. chelonae-abscessus group. In M. fortuitum group, sensitivity was seen to amikacin (13.63%), cefoxitin (18.18%), imipenem (31.81%), ceftriaxone (22.72%), and cotrimoxazole (31.81%). Only 14.28% and 7.14% of M. smegmatis were sensitive to cotrimoxazole and amikacin, respectively. M. chelonae-abscessus group was resistant to all the antibiotics tested and showed only intermediate sensitivity to amoxicillin-clavulanic acid (50%) and gatifloxacin (25%). A variability in sensitivity to different antimicrobials exists in all groups. Hence, it is advisable to perform antimicrobial susceptibility test before commencement of therapy.