Comparison of the MB/BacT and BACTEC MGIT 960 system for recovery of mycobacteria from clinical specimens

Multicenter matched-pair study comparing BACT/ALERT® MP reagent systems for the recovery of mycobacteria from specimens other than blood

The BACT/ALERT® MP Reagent System is a broth culture medium for optimal detection and recovery of mycobacteria from clinical samples. The MP formulation was recently modified to improve detection and recovery times. A multicenter prospective matched pair study design was conducted to validate the performance of improved MP (MP-I) versus current MP (MP-C) bottles utilizing nonsterile and normally sterile samples, except blood, from patients suspected of having mycobacterial infections. A total of 1488 clinical samples were collected to obtain 212 mycobacteria samples by either or both MP culture bottles. MP-I and MP-C sensitivities were 86.6% and 81.4%, respectively, but the difference was not significant (P = 0.163) while specificities were 96.8% and 93.8%, respectively, and that difference was significant (P = 0.002). Overall recovery was 94.34% for MP-I and 88.68% for MP-C (recovery was 100% for both bottles with 52 seeded samples). Overall performance of MP-I was better than MP-C for sensitivity, specificity, and recovery.

Assessment of current diagnostic algorithm for detection of mixed infection with Mycobacterium tuberculosis and nontuberculous mycobacteria

BACKGROUND

The increasing pulmonary diseases are reported to be affected by mixed infection of Mycobacterium tuberculosis (MTB) and nontuberculous mycobacteria (NTM). In this study, our objective was to assess the efficiency of mycobacterial culture plus DNA sequencing to detect the mixed infections with MTB and various NTM organisms. We also aimed to investigate how efficiently GeneXpert detected MTB in mixed infections with NTM in in vitro models.

METHODS

A serial of mixed infection samples was generated by combining suspensions of MTB and five NTM bacteria, respectively. The mixed suspensions were further detected with GeneXpert and liquid culture plus DNA sequencing.

RESULTS

Overall, the GeneXpert assay exhibited promising capability to identify the presence of MTB at different proportions ranging from 1% to 99%. For the liquid culture, the subsequent DNA sequencing only detected the presence of NTM bacteria in the mixed samples, which the proportion of NTM ranged from 1% to 99%, including M. intracellulare, M. kansasii, M. abscessus, and M. fortuitum. For M. avium, DNA sequencing was able to identify the mixtures as M. avium infection in suspensions with no less than 10% M. avium bacteria, whereas only MTB was found in the other suspensions with less M. avium bacteria.

CONCLUSIONS

Our data demonstrate that the current diagnostic algorithm cannot yield a precise detection of mixed infections with MTB and NTM bacteria. The GeneXpert assay only identify MTB in the mixed samples, while the subculture plus DNA sequencing prefers to identify the NTM species with the higher growth rate. Further targeted molecular analysis by specific capture of multiple loci of mycobacterial species from specimens is urgently required to solve this diagnostic dilemma.

The Application of Xpert Mycobacterium tuberculosis/Rifampicin, Quantitative Polymerase Chain Reaction and High Resolution Melting Curve in the Diagnosis of Superficial Lymph Node TB

OBJECTIVE

The diagnostic sensitivity and specificity of conventional methods for superficial lymph node tuberculosis (LNTB) are not ideal. We evaluated several novel methods including Xpert Mycobacterium tuberculosis/rifampicin (Xpert MTB/RIF) technology, quantitative fluorescence Polymerase Chain Reaction (qPCR) and High-Resolution Melting Curve (HRMC) in the diagnosis of superficial lymph node TB.

METHODS

Specimens from eighty-one consecutive patients with suspected LNTB and thirteen cases with other lymph node disease were analyzed by Xpert MTB/RIF, qPCR, and HRMC.

RESULTS

Among 81 patients with clinical suspicion of LNTB, there were 74 (91.4%) cases positive Mycobacterium tuberculosis Complex (MTBC) of Xpert MTB/RIF, 60 (74%) positive of qPCR, 24 (29.6%) of positive of BACTEC MGIT960 culture, and 13 (16%) cases positive of Roche culture. 38 cases (46.9%) were diagnosed with LNTB. All test methods showed a diagnostic specificity of 100% for LNTB. The sensitivity of molecular biology techniques was significantly higher than that of the traditional diagnostic methods, and Xpert MTB/RIF was the most sensitive diagnostic assay. On Rifampinresistant detection, Xpert MTB/RIF detected three cases (3.7%) with rpoB gene mutation, and Mycobacterium tuberculosis susceptibility testing detected 2 rifampicin-resistant cases (2.4%) which were consistent with Xpert MTB/RIF results. In the Isoniazid-resistant, 7 cases (8.1) of isoniazid resistance mutations (8.1%) were detected by HNC and 1 case was confirmed by Isoniazid susceptibility test.

CONCLUSION

Molecular detection increased the diagnostic sensitivity of LNTB and improved the detection sensitivity for rifampin and isoniazid resistance strain.

Biosensor-based detection of tuberculosis

Tuberculosis (TB), caused byMycobacterium tuberculosis(M.tb.), is one of the most prevalent and serious infectious diseases worldwide with an estimated annual global mortality of 1.4 million in 2010.

Probability of negative mycobacterium tuberculosis complex cultures based on time to detection of positive cultures: a multicenter evaluation of commercial-broth-based culture systems

We conducted a multicenter study to determine whether Mycobacterium tuberculosis complex (MTBC) cultures in automated broth-based systems could reliably be considered negative sooner than 6 weeks. Laboratory sites used Bactec MGIT or BacT/Alert and tracked results of time to detection of all mycobacteria (TTD-all, n = 1547) and of MTBC (TTD-MTBC, n = 466) over 6-month periods from primarily (93%) respiratory specimens. Cumulative percentages by day detected and median TTD of initial and follow-up specimens were analyzed. The median TTD-MTBC for MGIT (n = 6 sites) was 14 days. For laboratories using standard processing procedures, 100% of MTBC were detected from initial and follow-up specimens in 28 and 35 days, respectively, and no yield of MTBC on solid or MGIT liquid media was observed after 5 weeks. The median TTD-MTBC for BacT/Alert (n = 3 sites) was 18 days, with 95% and 100% detected within 37 and 42 days, respectively. Analysis of TTD of positive MTBC cultures in broth can predict the probability of culture negativity at defined time points. Receipt of interim negative reports earlier than 6 weeks could assist clinicians in considering alternative diagnoses and could alter the timing and prioritization of public health interventions. Laboratories should analyze their own TTD data to inform protocol decisions. Laboratories using MGIT could issue reports of no growth of MTBC on initial specimens as early as 4 weeks and for patients undergoing treatment as early as 5 weeks postinoculation.

Comparison of the conventional culture, the manual fluorescent MGIT system and the automated fluorescent MGIT 960 culture system for the detection of Mycobacterium avium ssp. avium in tissues of naturally infected hens

Different methods for the detection of Mycobacterium avium ssp. avium (MAA) in naturally infected hens were compared. They included the conventional culture method (solid Herrold's and Stonebrink media and liquid Sula medium) and newly developed liquid culture systems, the manual mycobacteria growth indicator tube (M-MGIT) and the fully automated BACTEC MGIT 960 system (A-MGIT). 152 tissues originating from 15 naturally infected hens have been processed. The overall detection rates (percentage of positive cultures from the number of positive cultures determined by all the methods together) were 60, 70 and 76 % for the conventional media, M-MGIT and A-MGIT systems, respectively, the mean time of mycobacteria detection being 32.6, 17.6 and 14.6 d, respectively. The lowest contamination rate (2.0 %) was found in A-MGIT compared with M-MGIT (4.6 %) and conventional media (10.4 %).

Molecular identification of Mycobacterium chimaera as a cause of infection in a patient with chronic obstructive pulmonary disease

This report describes a case of Mycobacterium chimaera infection in a patient with a history of chronic obstructive pulmonary disease where the organism was identified by using molecular methods. M. chimaera was identified from fresh lung tissue and from an instrument-negative mycobacterial growth indicator tube broth culture. The utility of using sequence analysis of the internal transcribed spacer region for the rapid identification of a slow-growing nontuberculous Mycobacterium spp. where conventional culture methods were not successful was shown.

Differences in time to detection and recovery of Mycobacterium spp. between the MGIT 960 and the BacT/ALERT MB automated culture systems

Mycobacterium sp. recovery and time to detection were compared in the MGIT 960 and BacT/ALERT MB automated broth culture systems. The MGIT 960 demonstrated shorter time to detection (13.5 versus 25.2 days) and greater sensitivity (100% versus 66.6%) for recovery of the Mycobacterium tuberculosis complex than the BacT/ALERT MB system.

The use of variable-number tandem-repeat mycobacterial interspersed repetitive unit typing to identify laboratory cross-contamination with Mycobacterium tuberculosis

A retrospective study including 515 Mycobacterium tuberculosis isolates from 215 patients was conducted to investigate possible laboratory contamination with M. tuberculosis over a 1-year period in a university hospital. All cultures underwent variable-number tandem-repeat (VNTR) typing. Cultures suspected of being contaminated in the VNTR analysis and possible sources of contamination underwent mycobacterial interspersed repetitive unit (MIRU) typing further. Overall, 8 (3.7%) cases of 215 patients were considered possible false-positives. Five (2.3%) cultures might be contaminated during initial batching processing, and 1 (0.5%) and 4 (1.9%) cultures of them were further classified as presumed and possible cases, respectively, of cross-contamination on clinical grounds. Three (1.4%) cultures might be contaminated by cultures that had been processed in species identification procedures in the same laminar-flow hood. The 2-step strategy using VNTR and MIRU analyses in combination in this study appears to be a valuable means for the study of false-positive cultures.

Meta-analysis of BACTEC MGIT 960 and BACTEC 460 TB, with or without solid media, for detection of mycobacteria

In a meta-analysis of 10 studies, the BACTEC 960/MGIT and BACTEC 460 systems showed a sensitivity and specificity in detecting mycobacteria (1,381 strains from 14,745 clinical specimens) of 81.5 and 99.6% and 85.8 and 99.9%, respectively. Combined with solid media, the sensitivity of the two systems increased to 87.7 and 89.7%, respectively.

Multicenter evaluation of the fully automated bactec MGIT 960 system and three molecular methods for the isolation and the identification of mycobacteria from clinical specimens

A combination of Bactec MGIT 960 system, a PCR-based assay and a PCR-Restriction Analysis procedure (PRA) was assessed for the detection and identification of mycobacteria from clinical samples. The MGIT recovered 243 from 266 mycobacterial isolates. The PCR-based assay correctly identified all (234) Mycobacterium tuberculosis isolates, while 35 nontuberculous mycobacterial isolates were identified by PRA.

Susceptibility testing with the manual mycobacteria growth indicator tube (MGIT) and the MGIT 960 system provides rapid and reliable verification of multidrug-resistant tuberculosis

The objective of the study was to compare the manual Mycobacteria Growth Indicator Tube (MGIT) method and the BACTEC MGIT 960 system to the BACTEC 460 method for susceptibility testing of Mycobacterium tuberculosis. The evaluation was based on testing of 36 M. tuberculosis strains with various susceptibilities to isoniazid (INH), rifampin (RMP), ethambutol (EMB), and streptomycin (SM). In addition, five of the strains generating discrepant results in testing for EMB were analyzed for heteroresistance. For INH, the susceptibility test results obtained by the MGIT 960 and the manual MGIT systems agreed with the BACTEC 460 results in 94 and 97% of the cases, respectively. The results of susceptibility to RMP were all in agreement. For SM, 78 and 72% of the results obtained by the MGIT 960 and the manual MGIT systems, respectively, agreed with the BACTEC 460 results. In contrast, less than 80% of the results for susceptibility to EMB obtained by the two MGIT methods agreed with the BACTEC 460 results. All five strains analyzed for EMB heteroresistance were found to consist of resistant and susceptible subpopulations. The average turnaround times were 6.4 days for the MGIT 960 system, 6.5 for the manual MGIT system, and 8.7 days for the BACTEC 460 method. Both MGIT methods can be regarded as accurate and rapid alternatives to the BACTEC 460 method for detection of strains resistant to INH and RMP. However, more studies are needed for solving the problems associated with susceptibility testing to EMB and SM.

Evaluation of BacT/Alert 3D liquid culture system for recovery of mycobacteria from clinical specimens using sodium dodecyl (lauryl) sulfate-NaOH decontamination

A total of 52 mycobacterial isolates were recovered from 1,197 clinical specimens decontaminated by a sodium dodecyl (lauryl) sulfate (SDS)-NaOH protocol. Of these, 94% were recovered with the BacT/Alert 3D system (Organon Teknika, Durham, N.C.) and 79% were recovered on Löwenstein-Jensen (LJ) medium. Mean times to detection of organisms of the Mycobacterium tuberculosis complex (n = 47) were 22.8 days with LJ medium and 16.2 days with the system. The BacT/Alert 3D system is a rapid and efficient detection system which can be used with an SDS-NaOH decontamination procedure.

Comparison of MB/BacT system and agar proportion method in drug susceptibility testing of Mycobacterium tuberculosis

The drug susceptibilities of 105 isolates/strains of Mycobacterium tuberculosis (101 clinical isolates and four control strains from the American Type Culture Collection) were assessed by the MB/BacT system and conventional agar proportion method. The agreement rates between the two methods were 99.0% for streptomycin, 95.2% for isoniazid and 100% for rifampin. The mean times to detection for drug-resistant isolates were 4.7 days (range: 2.5-13.7 days) using the MB/BacT system and 14.8 days (range: 14-21 days) using the agar proportion method. For drug-susceptible isolates, the times to detection were 10.8 days (mean) and 21 days respectively. Thus, these data have demonstrated that the automated, non-radiometric MB/BacT system is an efficient, accurate and reliable method for assessing drug susceptibilities of M. tuberculosis compared with the conventional agar proportion method.