Comparison of the MB/BacT and BACTEC 460 TB systems for recovery of mycobacteria from various clinical specimens

Evaluation of BACTEC 460 TB system for rapid in vitro screening of drugs against latent state Mycobacterium tuberculosis H37Rv under hypoxia conditions

Mycobacterium tuberculosis exhibits latent state due to its ability to survive for extended periods under oxygen depletion conditions. The conventional plating method employed for in vitro screening of antitubercular agents against latent state M. tuberculosis is laborious and time consuming exercise. Towards this end, BACTEC 460 TB system of antitubercular screening was evaluated for testing efficacy of antimicrobial agents in hypoxia induced model of latent tuberculosis, in vitro. In this study, drugs like isoniazid, metronidazole and rifampin were tested at concentrations- 2, 10 and 50 microg/ml for their antilatency activity by using BACTEC and conventional methods. Results obtained from both the methods were comparable (P>0.05) and a good correlation was observed between colony forming units and growth index values. Further, time to determine mycobacterial growth was significantly reduced (P<or=0.001) in BACTEC method (4-7 days) as compared to plating method (26-30 days). BACTEC method was found to be faster, cost effective and more sensitive as compared to plating method. Being rapid, reliable and reproducible, this method can be a promising alternative to conventional plating method for screening of potential antitubercular agents in in vitro models of latent tuberculosis.

New simple decontamination method improves microscopic detection and culture of mycobacteria in clinical practice

This study was carried out at Dr. Cetrángolo Hospital, Buenos Aires, Argentina. The objective was to compare two digestion-decontamination procedures: the N-acetyl-L-cysteine-sodium citrate-NaOH (NALC-NaOH) and a combination of 7% NaCl plus NaOH, the hypertonic saline-sodium hydroxide (HS-SH) method, in detection and recovery of mycobacteria. Microscopy detection rates before and after concentration of specimens by both methods, were also compared. The study had two phases. Phase I: comparison of the gold standard NALC-NaOH and HS-SH on paired samples involving respiratory clinical specimens by means of receiver operating characteristic curve analysis. Phase II: blinded, randomized trial to assess the performance of HS-SH versus NALC-NaOH in clinical practice. Phase I: Positive microscopy rate was significantly increased in around 2.2% after concentration in comparison to that of specimens without concentration. The calculated sensitivity values for microscopy detection increased between 15.2% (HS-SH: 73.5%) to 16.7% (NALC-NaOH: 75.0%) over those without concentration (58.3%). Phase II: similar diagnostic rates by microscopy and cultures were obtained by either HS-SH or NALC-NaOH. The clinical performances were also very similar. These results and the low cost of the HS-SH procedure indicate the possibility of its implementation in clinical laboratories with high burden of tuberculosis cases and low resources.

Tuberculosis prevention and control in long-term-care facilities for older adults

In the United States, older adults comprise 22% of cases of tuberculous disease but only 12% of the population. Most cases of tuberculosis (TB) occur in community dwellers, but attack rates are highest among frail residents of long-term-care facilities. The detection and treatment of latent TB infection and TB disease can pose special challenges in older adults. Rapid recognition of possible disease, diagnosis, and implementation of airborne precautions are essential to prevent spread. It is the intent of this evidence-based guideline to assist healthcare providers in the prevention and control of TB, specifically in skilled nursing facilities for the elderly.

Evaluation of the MB/BacT system compared with Middlebrook 7H11 and Lowenstein-Jensen media for detection and recovery of mycobacteria from clinical specimens

MB/BacT vials (an automated system), Middlebrook 7H11 agar plates with the microcolony method for growth detection, and conventional Lowenstein-Jensen egg-based medium were assessed for their rates of recovery, time to detection and ease in aiding the identification of mycobacterial isolates. Of the 2101 consecutive, non-selected specimens for tuberculosis analysed in the laboratory, 158 (7.5%) yielded growth of 159 mycobacteria on at least one of the three media, comprising 111 Mycobacterium tuberculosis and 48 non-tuberculous mycobacteria. Of the 111 specimens positive for M. tuberculosis, 100 isolates were recovered from MB/BacT vials, 99 from M7H11 agar plates, and 86 from Lowenstein-Jensen tubes. The combination of MB/BacT and M7H11 recovered 110 isolates of M. tuberculosis, 107 from M7H11 and Lowenstein-Jensen, and 105 from MB/BacT plus Lowenstein-Jensen. The average time to detection of M. tuberculosis was 11 days with M7H11 using the microcolony method, 16 days with MB/BacT, and 19.5 days with the conventional Lowenstein-Jensen method. The MB/BacT vials recovered greater numbers of non-tuberculous mycobacteria than either of the other two media, but these were considered mostly to be saprophytes. It was concluded that a combination of media was better than a single medium. None of the media combinations showed statistical differences. Use of M7H11 with the microcolony method, which shortens the detection time for mycobacteria and facilitates the detection of mixed cultures, together with the Lowenstein-Jensen tube, was a useful combination.

The evaluation of FASTPlaqueTB test for the rapid diagnosis of tuberculosis

FASTPlaqueTB (Biotec Laboratories Ltd., Ipswich, UK) is a rapid test which utilizes bacteriophage amplification technology for the detection of viable Mycobacterium tuberculosis in clinical specimens. We evaluated performance of the FASTPlaqueTB test by comparing with BACTEC 460 TB culture system (Becton Dickinson Co., Maryland, USA), polymerase chain reaction (PCR) and acid fast bacilli (AFB) smear methods. We investigated 192 sputum specimens collected from the patients suspected of having pulmonary TB by AFB smear, BACTEC 460 TB culture system, PCR and FASTPlaqueTB test. The sensitivity of AFB smear, PCR and FASTPlaqueTB test were 57.8%, 84.4% and 87.5% respectively when we accepted BACTEC 460 TB culture system as gold standard. We conclude that FASTPlaqueTB test has a good potential for rapid diagnosis of Mycobacterium tuberculosis as a result of the evaluation of these three tests by comparison to the BACTEC 460 TB culture system.

Comparison of the sodium dodecyl sulfate-sodium hydroxide specimen processing method with the C18-carboxypropylbetaine specimen processing method using the MB/BacT liquid culture system

The ability of physicians to diagnose tuberculosis is impacted by the use of smear and culture techniques combined with specimen processing methods. The objective of this study was to evaluate the effects of specimen processing on smear and culture sensitivity by comparing the specimen processing method that uses C(18)-carboxypropylbetaine with the method that combines sodium dodecyl sulfate and sodium hydroxide. A total of 1,201 specimens were entered into this study. Specimens were split approximately equally such that one-half of each specimen was processed with sodium dodecyl sulfate-sodium hydroxide, while the other half was processed with C(18)-carboxypropylbetaine. All sediments were subjected to acid-fast staining and then analyzed using the MB/BacT liquid culture system (bioMérieux, France) and solid media. The sensitivity of smear following processing with sodium dodecyl sulfate-sodium hydroxide and C(18)-carboxypropylbetaine was 61.2% and 58.6% (P>0.05), respectively, while the specificities were identical (99.7%). The sensitivity of culture was 84.2% and 96.1% (P<0.05), respectively. The time to detection in the MB/BacT liquid culture system was 13.2+/-5.6 and 15.0+/-8.8 days (P>0.05), respectively, and 20.0+/-7.6 and 15.7+/-8.9 days (P<0.05), respectively, on solid media. The contamination rates in the MB/BacT system were 0.8% and 8.7%, respectively, whereas the contamination rates on solid media were 2.6% and 4.3%, respectively. C(18)-carboxypropylbetaine specimen processing was less labor-intensive than sodium dodecyl sulfate-sodium hydroxide processing and improved the ability of laboratory staff to detect the presence of mycobacteria by culture.

Evaluation of the MB/BacT system for recovery of mycobacteria from clinical specimens in comparison to Lowenstein-Jensen medium

OBJECTIVE

To evaluate the performance of the MB/BacT system (Organon Teknika) in comparison to Lowenstein-Jensen (LJ) solid medium for recovery of mycobacteria from clinical specimens.

METHODS

Two thousand three hundred and ten specimens (1626 respiratory, 593 urine, 60 body fluids, five tissue and 26 others) were inoculated in MB/BacT (0.5 mL) and on two LJ slants (0.25 mL each). N-acetyl-l-cysteine-NaOH (final concentration 2%) was used for decontamination.

RESULTS

Two hundred and fifty-one (10.8%) mycobacterial isolates [190 Mycobacterium tuberculosis complex (MTBC) and 61 non-tuberculous mycobacteria (NTM)] were detected. Of these 251 isolates, 234 (93.2%; 181 MTBC and 53 NTM) were detected in MB/BacT and 169 (67.3%; 154 MTBC and 15 NTM) on LJ. The mean (median) times to detection of MTBC by MB/BacT and LJ were 13.8 (13) and 22.1 (20) days, respectively, while overall contamination rates were 7.7% and 8.1%, respectively.

CONCLUSIONS

Sensitivity and time to detection were significantly better with MB/BacT than with solid LJ medium.

Evaluation of automated BACTEC MGIT 960 system for testing susceptibility of Mycobacterium tuberculosis to four major antituberculous drugs: comparison with the radiometric BACTEC 460TB method and the agar plate method of proportion

We evaluated the performance of BACTEC MGIT 960 for automated testing of the susceptibility of 133 strains of Mycobacterium tuberculosis to streptomycin, isoniazid, rifampin, and ethambutol. The BACTEC MGIT 960 results were compared with those obtained with the radiometric BACTEC 460TB system, and when there was disagreement, the method of proportion on agar plates was used as a reference method. Strains resistant to the critical concentration of streptomycin, isoniazid, or ethambutol were also tested with a second, higher concentration. The overall agreement between the two systems was 96.7%, and the 18 discrepancies were resolved in favor of BACTEC 460TB in 11 cases and in favor of BACTEC MGIT 960 in 7, a difference which was not statistically significant. Apart from the assay's low specificity for ethambutol, which was low for the radiometric assay as well, good sensitivity and specificity values characterized BACTEC MGIT 960. The average time required for completion of the test was 2.5 days shorter with BACTEC 460TB. In conclusion, BACTEC MGIT 960 appears to be a suitable replacement for the radiometric method of antimicrobial susceptibility testing of M. tuberculosis. The problem of frequent contamination of BACTEC MGIT 960 tests needs to be quickly resolved; in fact, 14 strains had to be reprocessed because of contamination.

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.

Identification of 54 mycobacterial species by PCR-restriction fragment length polymorphism analysis of the hsp65 gene

A total of 121 reference and clinical strains of both slowly and rapidly growing mycobacteria belonging to 54 species were studied for restriction fragment length polymorphism of a PCR-amplified 439-bp segment of the gene encoding the 65-kDa heat shock protein. Restriction digests were separated by 10% polyacrylamide gel electrophoresis (PAGE). By including a size standard in each sample, the restriction fragment profile was calculated using a computer-aided comparison program. An algorithm describing these 54 species (including 22 species not previously described) is proposed. We found that this assay based on 10% PAGE provided a more precise estimate than that based on agarose gel electrophoresis of the real size of restriction fragments as deduced from the sequence analysis and allowed identification of mycobacteria whose PCR-restriction fragment length polymorphism analysis patterns were unequivocally identified by fragments shorter than 60 bp.

Comparison of MB/Bact alert 3D system with radiometric BACTEC system and Löwenstein-Jensen medium for recovery and identification of mycobacteria from clinical specimens: a multicenter study

The MB/BacT ALERT 3D System (MB/BacT) (Organon Teknika, Boxtel, The Netherlands) is a fully automated, nonradiometric system with a revised antibiotic supplement kit designed for the recovery of mycobacteria from clinical specimens. In a multicenter study, the recovery rate of acid-fast bacilli (AFB) and the mean time to their detection from clinical specimens was determined by using the MB/BacT system. Data were compared to those assessed by the radiometric BACTEC 460 system (B460) and by culture on Löwenstein-Jensen (L-J) solid medium. A total of 2,859 respiratory and extrapulmonary specimens were processed by the N-acetyl-L-cysteine (NALC)-NaOH method using two different concentrations of sodium hydroxide; 1.5% was adopted in study design A (1,766 specimens), and 1.0% was used in study design B (1,093 specimens). The contamination rates for MB/BacT were 4.6% (study design A) and 7.1% (study design B). One hundred seventy-nine mycobacterial isolates were detected by study design A, with 148 Mycobacterium tuberculosis complex (MTB) isolates and 31 nontuberculous mycobacteria (NTM) isolates. Overall recovery rates were 78.8% for MB/BacT (P = 0.0049), 64.2% for L-J (P < 0.0001), and 87.1% for B460, whereas they were 84.5, 70.9, and 91.2%, respectively, for MTB alone. A total of 125 mycobacteria were detected by study design B, with 46 MTB and 79 NTM. Overall recovery rates by the individual systems were 57.6% (P = 0.0002), 56.8% (P = 0.0001), and 80% for MB/BacT, L-J, and B460, respectively, whereas the rates were 91.3, 78.3, and 97.8% for MTB alone. By study design A, the mean times to detection of smear-positive MTB, smear-negative MTB, and NTM were 11.5, 19.9, and 19.6 days, respectively, with the MB/BacT; 8.3, 16.8, and 16.6 days, respectively, with the B460; and 20.6, 32.1, and 27.8 days, respectively, with L-J medium. By study design B, the mean times were 15.1, 26.7, and 26 days with the MB/BacT; 11.7, 21.3, and 24.8 days with the B460; and 20.4, 28.7, and 28.4 days with L-J medium. Identification was attempted by probing (Accuprobe) MB/BacT-positive bottles within the first working day following instrument positive flag. Results were compared to those obtained in the B460 positive vials by the p-nitro-alpha-acetylamino-beta-hydroxypropiophenone (NAP) test (study design A) or by the Accuprobe assay (study design B). About 90% of MTB and 100% of NTM could be identified, showing turnaround times closely related to those obtained by combining B460 and the NAP test or the Accuprobe assay. In conclusion, even though recovery rates were shown to be lower than B460, especially for NTM, and contaminants were somewhat higher, MB/BacT represents a valuable alternative to the radiometric system, especially in those laboratories where disposal of radioactive waste is restricted. Finally, when AFB are cultured in nonradiometric liquid media, our data (detection times and bacterial overgrowth rates) suggest that decontamination with 1.5% NaOH may be more suitable than the standard NALC-NaOH.

Direct identification of Mycobacterium avium complex and Mycobacterium gordonae from MB/BacT bottles using AccuProbe

We evaluated the ability of the AccuProbe (Gen-Probe, San Diego, Calif.) to detect Mycobacterium gordonae and Mycobacterium avium complex directly in liquid medium flagged positive by the MB/BacT (Organon Teknika Corp., Durham, N.C.). Seventy-one bottles from clinical specimens containing M. gordonae and 34 containing M. avium, confirmed by culture, were tested by direct AccuProbe assay for both organisms after additional incubation for > or = 48 h and centrifugation at 4,500 x g for 15 min. Relative light unit (RLU) values were analyzed using the manufacturer's recommended cutoff of 30,000 RLU and a lower cutoff of 10,000 RLU. Using the 30,000 RLU cutoff, 55 of 71 (77.5%) specimens containing M. gordonae yielded positive results, whereas 28 of 34 (82.3%) M. avium complex specimens were correctly identified by direct probe. No specimens shown by culture to contain either M. gordonae or M. avium complex tested positive with the probe for the opposite organism (100% specificity). When the cutoff was lowered to 10,000 RLU, 67 of 71 M. gordonae (94.4%) and 32 of 34 M. avium complex (94.1%) specimens were correctly identified. This difference was significant for M. gordonae (P = 0.004) but not for M. avium complex (P = 0.26) compared to detection using the recommended RLU cutoff. Specificity was 100% for specimens containing M. gordonae that were tested with the M. avium complex probe using the 10,000 RLU cutoff, whereas specificity for specimens containing M. avium complex tested with the M. gordonae probe was 97%. Using a lower RLU cutoff for determining a positive result using the M. gordonae or M. avium complex probes when testing instrument-positive MB/BacT bottles directly will improve sensitivity without substantially compromising specificity.

Comparison of Mycobacterium tuberculosis susceptibility testing performed with BACTEC 460TB (Becton Dickinson) and MB/BacT (Organon Teknika) systems

The recently introduced automated culture systems MB/BacT (Organon Teknika, Belgium) was compared with radiometric BACTEC 460TB (Becton Dickinson, USA) to test antimicrobial susceptibility of Mycobacterium tuberculosis to first line drugs. On 113 strains 97.5% agreement was obtained, with the difference being not significant. Concordance was practically complete for the most important drugs, isoniazid and rifampin. The two methods however significantly differed for the time needed to complete the test; in fact MB/BacT required on the average five days more than BACTEC 460TB. Despite the delay in the completion of the test, the excellent reliability along with the elimination of radioactivity and full automation make MB/BacT an attractive alternative for susceptibility testing of M. tuberculosis.

Comparison of BACTEC MGIT 960 and BACTEC 460 for culture of Mycobacteria

We have compared the BACTEC 460 system with the BACTEC MGIT 960 system for culture of mycobacteria from 1800 routine clinical specimens. Rate of isolation of M. tuberculosis and time to detection of positive culture was comparable for both systems (BACTEC 460, 35 isolates, BACTEC MGIT 960, 34 isolates). Contamination of cultures was more common with the BACTEC MGIT 960 system. With intensification of the decontamination process an acceptable contamination rate was achieved in the BACTEC MGIT 960 system but time to detection of positive culture was increased by 1 to 2 days.

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

A total of 543 specimens were cultured in parallel with the MB/BacT and BACTEC MGIT 960 systems and on the conventional solid media. Mycobacteria were identified from 95 (17.5%) specimens, including 63 (66.3%) Mycobacterium tuberculosis and 32 (33.7%) nontuberculous mycobacteria. The recovery rates for the MB/BacT, MGIT 960, and solid media were 91.6, 87.4, and 54.7%, respectively, for all mycobacteria; the recovery rates were 93.6, 88.9, and 63.4%, respectively, for M. tuberculosis complex alone, and 87.5, 84.4, and 37.5%, respectively, for all nontuberculous mycobacteria. The mean times to detection of all mycobacteria by individual systems were 13. 9, 8.7, 31.7 days for the MB/BacT, MGIT 960 and solid media, respectively, 13.9, 9.3, 32.9 days for M. tuberculosis alone, and 14. 1, 8.1, 27.2 days for all nontuberculous mycobacteria. The contamination rates of the MB/BacT and MGIT 960 were 10.2 and 5.4%, respectively. With regard to detection times and recovery rates, both automated systems are superior to the conventional media (all p < 0.005). As compared to the MB/BacT, the MGIT 960 detected mycobacterial growth more rapidly (p < 0.001), and had a lower contamination rate (p = 0.003); however, there was no statistically significant difference in recovery rates between these two systems. These results indicate that both MGIT 960 and MB/BacT systems are rapid, sensitive, and efficient methods for the recovery of mycobacteria from clinical specimens.

Accelerated detection and identification of mycobacteria with MGIT 960 and COBAS AMPLICOR systems

An automated cultivation system for mycobacteria, the MGIT 960 system (MGIT system), was compared in the clinical routine with two variants of Löwenstein-Jensen (L-J) medium. A total of 152 isolates were recovered from 2,015 specimens: 139 (91%) with the MGIT system and 127 (84%) with L-J media (P = 0.05). These included 68 isolates of Mycobacterium tuberculosis, of which 88% grew in the MGIT system and 93% grew in L-J media (P = 0.389), and 84 isolates of mycobacteria other than M. tuberculosis (MOTT), of which 94% grew in the MGIT system and 76% grew in L-J media (P = 0.003). More M. avium complex isolates were detected in the MGIT system (n = 65) than in L-J media (n = 50) (P = 0.001). Growth in the MGIT system was detected in 2 weeks for 78% of the isolates, whereas growth was detected in the two L-J media for 17 and 25% of the isolates, respectively. The mean times to detection of M. tuberculosis were 12 days in the MGIT system and 20 days in L-J media, and for M. avium complex the mean times to detection were 8 and 22 to 25 days, respectively. The contamination rates were similar (8.7 to 8.9%) in all media. A commercial amplification system (COBAS AMPLICOR) was evaluated for its ability to rapidly identify M. tuberculosis, M. avium, and M. intracellulare directly from 393 samples in MGIT system broth. A correct PCR result, as evaluated by culture or clinical data, was obtained for 96% of the samples, with inhibition being detected for 2% of the samples. Of the 89 results positive for M. tuberculosis, 91% were regarded as true positive, 8% were regarded as inconclusive, and 2% were considered false positive. For results positive for M. avium and M. intracellulare, 97 and 79%, respectively, were regarded as true positive. Increased rapidity and enhanced isolation of MOTT were obtained with the MGIT system. COBAS AMPLICOR was suitable for rapid identification of these three common pathogens from MGIT system broth.

A cell viability assay based on monitoring respiration by optical oxygen sensing

A cell viability assay based on monitoring of the metabolic activity of living cells via their consumption of dissolved oxygen has been developed. It uses a microwell plate format and disposable phosphorescent sensor inserts incorporated into each sample. The wells are subsequently sealed from ambient oxygen using a layer of mineral oil, and periodically scanned from underneath with a simple fiber-optic phosphorescent phase detector. Thus, dissolved oxygen levels and time profiles of cell respiration can be determined noninvasively and compared to each other. The system was tested by monitoring the viability of the fission yeast Schizosaccharomyces pombe. In comparison with the conventional cell densitometry assay, the optical oxygen sensor method could reliably monitor lower numbers of cells (10(4)-10(5) vs 10(6)-10(7) cells/ml for densitometry), and accurately determine culture viability within 1 h. The assay was then applied to determine the viability of samples treated with toxic agents such as azide and in response to expression of a physiological inducer of cell death, the Bcl-2 family member Bak. The results obtained confirm that measurement of cell respiration by this assay can serve as a predictable, reliable, and fast method for high-throughput determination of cell viability and growth.

Reliability of the MB/BacT system for testing susceptibility of Mycobacterium tuberculosis complex isolates to antituberculous drugs

The susceptibility of 115 Mycobacterium tuberculosis complex clinical isolates to isoniazid, streptomycin, ethambutol, and rifampin was assessed by the MB/BacT and BACTEC 460TB systems. The correlation between the two tests was 98.3% for isoniazid, 100% for streptomycin and rifampin, and 95.8% for ethambutol. Turnaround times for antimicrobial susceptibility testing ranged from 5 to 11 days (median, 8.5 days) for MB/BacT and from 4 to 8 days (median, 6 days) for BACTEC 460TB.

Evaluation of the BACTEC MGIT 960 and the MB/BacT systems for recovery of mycobacteria from clinical specimens and for species identification by DNA AccuProbe

A total of 120 mycobacterial isolates were recovered from 1,068 clinical specimens. Of these, 82.5% were in MGIT 960, 83.3% were in MB/BacT, 80% were in BACTEC 460, and 70% were on Löwenstein-Jensen medium. Mean times to detection of Mycobacterium tuberculosis (n = 96) were significantly shorter with MGIT 960 (12.6 days, P = 0.003) and BACTEC 460 (11.8 days, P < 0.001) than with MB/BacT (15.9 days). Although, MGIT 960 showed the lowest rate of recovery of M. kansasii genotype I (64.3%), the earliest growth was detected with this system (8.9 days). Low and similar rates of contamination were obtained with MGIT 960 (3.3%) and MB/BacT (3%). The AccuProbe test for identification showed excellent sensitivities with MGIT 960 (96. 8%) and MB/BacT (100%) cultures. In addition to being nonradiometric, both MGIT 960 and MB/BacT are accurate, rapid, and labor-saving detection systems which could replace the radiometric method.

Comparative evaluation of the MB/BacT and BACTEC 460 TB systems for the detection of mycobacteria from clinical specimens: clinical relevance of higher recovery rates from broth-based detection systems

New broth-based detection systems have higher recovery rates of mycobacteria from clinical specimens than traditional cultures on solid media. The clinical significance of this higher sensitivity rate is largely unknown. We prospectively evaluated the performances of two liquid media detection systems (the MB/BacT system and the BACTEC 460 TB system) and an egg-based Lowenstein-Gruft solid medium (LG) on the recovery rates of mycobacteria from 849 clinical specimens. Mycobacteria (other then M. gordonae) were detected in 51 (6.0%) specimens. In 12/51 (23%) specimens, mycobacteria (five mycobacterium tuberculosis (MtB) and seven non-M tuberculosis complex (MOTT) were recovered only from the broth-based systems. Review of the patients' clinical charts revealed that failure of LG to recover Mtb were due to nonmycobacterial overgrowth and antibiotic treatment. The recovered MOTT were all clinically nonsignificant. Higher sensitivity of broth-based mycobacteria detection systems is largely due to their capability to recover mycobacteria from treated tuberculous patients or from partially decontaminated specimens. The high recovery rates of nonclinically significant MOTT could potentially increase inappropriate use of antibiotics.

Comparison of MB/BacT and BACTEC 460 TB systems for recovery of mycobacteria in a routine diagnostic laboratory

MB/BacT, BACTEC 460 TB, and Löwenstein-Jensen (LJ) medium were evaluated in parallel for recovery of mycobacteria from 3,700 continuous clinical specimens in a routine laboratory. Mycobacteria were identified from 123 (3.3%) specimens. The recovery rates for all mycobacteria by the different systems were 91.0, 73.0, and 53.6% for BACTEC 460 TB, MB/BacT, and LJ medium, respectively. The recovery rates for Mycobacterium tuberculosis complex were 97.1, 80. 2, and 67.6%, respectively. The lack of sensitivity of the MB/BacT system was more pronounced with smear-negative specimens and resulted in a failure to detect three patients with infectious tuberculosis.