Rapid recovery of mycobacteria from clinical specimens using automated radiometric technic

Comparison of the Lowenstein-Jensen Medium, the Middlebrook 7H10 Medium and MB/BacT for the Isolation of Mycobacterium Tuberculosis (MTB) from Clinical Specimens

INTRODUCTION

Tuberculosis (TB) is the most common cause of death due to a single infectious agent worldwide in adults. India alone accounts for 30% of the global tuberculosis burden. There is a need for a method of cultivation of mycobacteria that is reliable and economical and has a short turnaround time.

OBJECTIVE

The present study was attempted to assess the feasibility of using MB BACT and Middlebrook 7h10(MB7H10) as primary isolation media for mycobacteria. They were compared with the LJ medium, which was the gold standard.

MATERIALS AND METHODS

Various clinical specimens from a total of 236 clinically suspected cases of TB were studied. All the samples were decontaminated by using the modified Petroff's method. Each sample was subjected to ZN staining and it was simultaneously inoculated onto the LJ medium, the MB7H10 medium and MB BACT. The growth from the cultures were confirmed by ZN staining and they were speciated by using biochemical reactions.

RESULTS

Out of the 236 samples which were screened, 116 isolates were obtained. All the 116 were isolated from MB BACT, 82 were isolated from the LJ medium and 62 were isolated from MB7H10. 82 isolates were obtained from MB BACT and the LJ medium, 62 were obtained from MB7H10 and MB BACT, 58 were isolated from LJ and MB7H10 and 58 were isolated from LJ medium, MB7H10 and MB bact. Neither the L J medium nor the Middlebrook 7h 10 medium could isolate mycobacteria exclusively. It showed that the combination of media did not prove to be superior over the use of MB BACT alone. The average isolation time of L J, the MB7H10 medium and MB BACT was 30.81 days, 31.06 days and 18.70 days.

INTERPRETATION AND CONCLUSION

MB BACT is a better medium as compared to the L J medium and the MB7H10 medium, both in terms of the number of isolates and the isolation rate. The MB BACT method proved to be a very speedy method and it could isolate mycobacteria 7-10 days earlier as compared to the L J medium and the Middlebrook 7 H10 medium.

Chemotherapy and diagnosis of tuberculosis

Since after the first streptomycin 1944 trials, anti-tuberculous chemotherapy research has been focused upon establishing drug combination regimens capable of overcoming drug resistance and amenable to ambulatory treatment in resource strapped countries. The first milestone being the 1959 Madras trial comparing home and sanatorium treatment in South India. Subsequently, the MRC trials led Fox and Mitchison to indicate rifampicin, isoniazid and pyrazinamide as the first line drugs for short course, 6 month, regimens and the 1982 Hong Kong Chest Service trials established intermittent therapy as the ambulatory treatment standard for directly observed therapy (DOT). The rising of the HIV epidemic at the beginning of the 1980s has refuelled tuberculosis spread in Africa and Asia and contributed to the expansion of drug-resistant tuberculosis worldwide making the development of new drugs and drug regimens for ambulatory treatment a top priority. Led by biotechnological advances, molecular biology has been brought into TB laboratory diagnosis for the highly sensitive and specific rapid identification of Mycobacterium tuberculosis in biological samples. The field of immunological diagnosis of TB infection, dominated since the early 1900s by the intradermal tuberculin reaction has been put back in motion by the discovery of M. tuberculosis-specific proteins and peptides, now employed in blood tests of high sensitivity and specificity for the diagnosis of latent TB which may help with the identification of contacts at higher risk of active disease and the eradication of epidemic cases.

Resuscitation factors from mycobacteria: homologs of Micrococcus luteus proteins

SETTING

Resuscitation promoting factors (Rpfs) are proteins, originally identified in Micrococcus luteus, that promote recovery of bacteria from a viable but non-replicating phase (e.g., stationary phase or latency) to a replicating phase. Purified M. luteus Rpf can stimulate growth and increase recovery of M. luteus bacteria as well as Mycobacterium tuberculosis bacteria from prolonged stationary cultures.

OBJECTIVE

To clone and characterize Rpfs from mycobacteria.

DESIGN

We cloned one M. avium subsp. paratuberculosis rpf gene and one M. tuberculosis rpf gene into the pET19b or pET21a vector for expression in Escherichia coli. The His-tag recombinant proteins were purified and characterized.

RESULTS

When the purified recombinant proteins were added to Sauton medium (a relatively minimal medium) at 100-500 pM, lag phase for mycobacteria from non-replicating cultures was shortened and there was a 10- to 100-fold increase in colony-forming units compared with control samples. In most probable number assays, the mycobacterial Rpfs increased recovery of mycobacteria from late stationary culture by about 10-fold. The Rpfs also promoted recovery of extensively washed Mycobacterium smegmatis bacteria inoculated into Sauton medium. Rpfs had only minor effects on growth of M. tuberculosis in BACTEC 12B broth, a rich medium.

CONCLUSION

The mycobacterial Rpfs demonstrate resuscitation activities similar to those of the M. luteus Rpf.

Increased sensitivity of the BACTEC 460 mycobacterial radiometric broth culture system does not decrease the number of respiratory specimens required for a definitive diagnosis of pulmonary tuberculosis

The BACTEC 460 radiometric mycobacterial broth culture system has consistently demonstrated faster and increased recovery of Mycobacterium tuberculosis from respiratory specimens of patients with pulmonary tuberculosis than conventional culture methods. We thus questioned whether three sputa were still necessary to definitively diagnose pulmonary tuberculosis if the BACTEC radiometric culture system were in use. We performed a retrospective analysis of 430 sequential respiratory specimens submitted from 143 patients and from which M. tuberculosis had been recovered by in vitro culture and simultaneously assessed the diagnostic yield of acid-fast smear in this same cohort. M. tuberculosis was recovered from the first specimen for 117 (82%) of the 143 patients, from the second for 14 patients (10%; cumulative rate, 92%), and from the third for 12 patients (8%; cumulative rate, 100%). With the exception of those for bronchial brushings, recovery rates of M. tuberculosis were comparable for all respiratory specimen types (expectorated sputum, induced sputum, tracheal aspirates, bronchoalveolar lavage fluids). Only 46 (32%) of these 143 patients had acid-fast bacilli detected in smears; acid-fast bacilli were detected in the first submitted specimen for 44 patients (96%) and in the second for the remaining 2 patients (4%; cumulative rate, 100%). Culture- or smear-positive rates for sequential specimens obtained from AIDS patients were comparable to those for non-AIDS patients. Overall, the diagnostic culture yield of sequentially submitted specimens was not different from previously published studies in which the BACTEC radiometric culture system had not been used. Despite the documented enhanced ability of the BACTEC 460 radiometric mycobacterial culture system to recover M. tuberculosis more often and faster than conventional methods, three sequential respiratory specimens (regardless of type) were still necessary to definitively diagnose pulmonary tuberculosis.

Two liquid medium systems, mycobacteria growth indicator tube and MB redox tube, for Mycobacterium tuberculosis isolation from sputum specimens

Two manual liquid medium systems, the Mycobacteria Growth Indicator Tube (MGIT) and MB Redox tube systems, were evaluated in comparison to the radiometric BACTEC-460 semiautomated system for recovery of Mycobacterium tuberculosis from sputum specimens. The highest level of recovery, from a total of 77 culture-positive specimens, occurred with the BACTEC-460 system (92.2%), followed by the MB Redox tube (80.5%) and the MGIT (63.6%) systems. The shortest time to detection was observed also among the cultures in BACTEC-460: a mean of 12 days to a growth index (GI) of 10 and 15 days to a GI of 500. The mean times for the other systems were 16 days for the MB Redox tube system and 17.4 days for the MGIT system. The proportion of cultures grown after more than 3 weeks of incubation was only 2.8 or 8.4% in BACTEC-460 (for a GI of 10 or 500) but 17.7% in MB Redox and 22.5% in MGIT. Despite these differences in comparison to the BACTEC-460 system and some differences between the MGIT and MB Redox tube systems, either of the two manual liquid medium systems presents a reasonable alternative to the BACTEC-460 system, especially for laboratories with a limited workload, and a valuable element in the laboratory protocol, in conjunction with solid media, for obtaining rapid detection of growth from about 80% of culture-positive specimens and for better overall recovery of M. tuberculosis.

Rapid chemotaxonomic diagnosis of human tuberculosis

65 different clinical specimens from patients suspected of being infected with Mycobacterium tuberculosis were examined by three different diagnostic methods. Two of these methods were the conventional microscopic and cultural examinations. The third, a modern chemotaxonomical method is based upon the detection of tuberculostearic acid by GC-MS analysis using selected ion monitoring (GC-MS/SIM). Comparison of the results of the GC-MS analysis with those of the conventional methods has indicated that tuberculostearic acid analysis can be used for diagnosing tuberculosis under diagnostic routine conditions. The GC-MS method is rapid, usually providing results within 20 hours or less.

Current techniques in mycobacterial detection and speciation

Tuberculosis, a health concern so well controlled in recent decades that eradication seemed imminent, is once again reaching epidemic proportions following the increasing prevalence of AIDS. One important means of curbing this resurgence is a robust method that has the capability of identifying and speciating mycobacterial infections in a matter of days. Classic biochemical techniques, which require 4 to 8 weeks to identify and speciate tuberculosis infections, are in the process of being replaced by newer methods, including BACTEC, gene probes, nucleic acid amplification, amplification of ribosomal RNA, high-performance liquid chromatography, and gas chromatography-mass spectrometry. This review is intended to give the reader a synopsis of the current literature and research on these methods, including reliability, approximate time required for detection and speciation, and clinical utility.

Use of BACTEC radiometric culture method and polymerase chain reaction for the rapid screening of faeces and tissues for Mycobacterium paratuberculosis

The BACTEC radiometric culture method for detection of Mycobacterium paratuberculosis was evaluated on faeces from cattle on a farm in quarantine for Johne's disease. A multiplex polymerase chain reaction (PCR) based on the IS900 sequence specific for M paratuberculosis and a genus specific 16S rRNA region was developed and used to test cultures showing evidence of mycobacterial growth in the BACTEC liquid radiometric culture medium. Using the BACTEC-PCR combination, confirmation of M paratuberculosis from faeces and tissue of clinically affected animals was achieved within 2 to 4 weeks and 1 week, respectively, a substantial improvement on traditional culture and identification methods. The PCR provided rapid exclusion of M paratuberculosis when other Mycobacterium spp were grown. The radiometric culture medium proved to be very sensitive for culturing Mycobacterium spp.

Comparison of recovery rates for mycobacteria from BACTEC 12B vials, Middlebrook 7H11-selective 7H11 biplates, and Lowenstein Jensen slants in a public health mycobacteriology laboratory

Recovery rates from Middlebrook 7H11-selective 7H11 biplates and Lowenstein-Jensen slants (LJ) used with BACTEC 12B vials were compared for 5,399 specimens. For 578 specimens that were inoculated onto three media, 580 mycobacteria were isolated, including 277 (48%) Mycobacterium avium complex isolates, 230 (40%) Mycobacterium tuberculosis isolates, and 73 (12%) other mycobacteria. For BACTEC 12B vials, 506 (87%) cultures were positive, 45 (8%) were negative, and 29 (5%) were lost to contamination; for 7H11-7H11-selective biplates, 469 (81%) cultures were positive, 95 (16%) were negative, and 16 (3%) were lost to contamination; for LJ, 230 (40%) cultures were positive, 111 (19%) were negative, and 239 (41%) were lost to contamination. For routine cultures, use of plate media is superior to use of LJ.

Simple and rapid detection of Mycobacterium tuberculosis complex organisms in bovine tissue samples by PCR

Mycobacterium bovis is a slowly growing microorganism, and confirmation of the diagnosis by conventional culture is a lengthy process. A simple, rapid method for the extraction of DNA from bovine tissue samples was developed and used in a PCR designed for the diagnosis of tuberculosis. Tissues from 81 cattle from tuberculosis-infected herds (group 1) and 19 cattle from tuberculosis-free herds (group 2) were tested in this PCR, and the results were compared with those of conventional culture. The PCR assay detected 71.4% of the culture-positive animals from group 1. Tissue from all animals in group 2 were negative in the PCR assay and by culture. The described method could be used as a rapid screening technique which would be complementary to culture of tissue specimens for the routine diagnosis of bovine tuberculosis. The PCR technique is much faster than culture and reduces the time for diagnosis from several months to 2 days. It also provides for the detection of M. bovis when rapidly growing Mycobacterium spp. are present in the sample and may be able to detect the presence of M. bovis in samples even when organisms have become nonviable.

Detection and identification of Mycobacterium directly from BACTEC bottles by using a DNA-rRNA probe

Detection and identification of mycobacterial species using DNA-rRNA probes from colonies has been used for some time. Guidelines for probe use with a specific minimum growth index (GI) cutoff from BACTEC 12B bottles or its use with 7H9 broth has not been defined. This study defined this minimum GI guideline. Clinical specimens received during the study period were decontaminated and directly inoculated into BACTEC 12B bottles and appropriate solid media. An initial probe test was performed at a GI reading of > or = 100. An additional probe test was made at GI of > or = 300. A total of 1377 specimens were processed with 98 specimens containing 99 isolates of Mycobacterium. Of these, 82 were M. avium complex (MAC), six were M. tuberculosis (Mtb), and 11 were other species. At a GI of > or = 100, 82% of MAC were detected; at a GI of > or = 300, 89% were detected. All Mtb were detected at a GI of > or = 100. The probes correctly identified all isolates from backup 7H9 broths. There were no false-positive probe results for any of the isolates from either BACTEC 12B or 7H9 media. Therefore, the DNA-rRNA probe test at a GI of > or = 300 saves considerable time (on average, 21 days saved) for the detection and identification of Mtb and MAC. This time saving compares with waiting for the production of colonies while retaining acceptable sensitivity and excellent specificity.

In vitro antimicrobial activity of benzoxazinorifamycin, KRM-1648, against Mycobacterium avium complex, determined by the radiometric method

MICs of a newly developed benzoxazinorifamycin derivative, KRM-1648, for Mycobacterium avium complex (MAC) were determined by the BACTEC 460 TB system and compared with those of other known antimicrobial agents. The radiometric method gave a fast, accurate, and reproducible MIC for each antimicrobial agent. MICs of KRM-1648 for 30 strains of MAC (10 strains each of M. avium isolated from AIDS and non-AIDS patients and of Mycobacterium intracellulare isolated from non-AIDS patients) were measured. The MICs, ranging from 0.004 to 0.0625 microgram/ml, were the lowest of all tested drugs, including rifampin, rifabutin, streptomycin, kanamycin, isoniazid, ethambutol, ofloxacin, ciprofloxacin, sparfloxacin, and clarithromycin. The MICs were 2 to 512 and 1 to 32 times lower than those of rifampin and rifabutin, respectively. With rifampin and ethambutol, there were some differences between the MICs for M. avium isolated from AIDS patients (American) and those for M. avium from non-AIDS patients (Japanese). Moreover, appreciable differences between the MICs of some drugs against M. avium and M. intracellulare isolated from non-AIDS patients were found. Many strains of M. avium were more susceptible to ofloxacin than M. intracellulare, but, conversely, M. avium was more resistant to rifampin, streptomycin, ethambutol, and clarithromycin than M. intracellulare.

Comparative evaluation of the MB-Check system for recovery of mycobacteria from clinical specimens

The performance of the MB-Check system (Roche) in the recovery of mycobacteria from clinical specimens was compared with that of the Bactec radiometric system and conventional culture on Löwenstein-Jensen medium. A total of 1,582 clinical specimens were used for the study; 74 yielded mycobacteria. Organisms of the Mycobacterium tuberculosis and Mycobacterium avium complexes accounted for the majority of isolates. The rate of recovery of all mycobacteria with the Bactec system was 91.9%, with the MB-Check system 79.7% and on Löwenstein-Jensen medium only 54.1%. Combination of the Bactec and MB-Check systems allowed recovery of 100% of isolates. The Bactec system showed a faster detection time than the other two methods.

Comparison of MB-Check, BACTEC, and egg-based media for recovery of mycobacteria

The rate of recovery and time to the detection of mycobacteria from clinical specimens were measured for biphasic (MB-Check; Nippon Roche Co., Ltd., Tokyo, Japan) and radiometric (BACTEC; Nippon Becton Dickinson Co., Ltd., Tokyo, Japan) liquid-based culture systems and egg-based media (3% Ogawa and Ogawa K). From the 245 sputum specimens processed, a total of 86 (35.1%) mycobacterial isolates were detected. Of these, 81 (94.2%) and 80 (93.0%) isolates were detected with the MB-Check and BACTEC systems, respectively, and 65 (75.6%) isolates were detected with the 3% Ogawa egg method. The difference in the percentages of positive cultures between the two systems based on liquid media and the 3% Ogawa egg method was significant (P less than 0.01). This difference was even greater among smear-negative specimens. The detection time was shorter with the liquid-based systems. The mean times to the detection of the Mycobacterium tuberculosis complex were 19.1 days with the MB-Check system, 13.4 days with the BACTEC system, and 21.7 days with the 3% Ogawa egg method. These results indicate that both the MB-Check and the BACTEC systems, based on liquid media, are efficient for the recovery of mycobacteria.

Use of polymerase chain reaction for rapid diagnosis of tuberculosis

A DNA amplification assay using the polymerase chain reaction technique designed for the rapid identification of Mycobacterium bovis organisms was used to test 211 human mycobacterial isolates and 177 clinical specimens previously submitted for routine mycobacterial culture. The procedures described could be used by routine or specialist laboratories for identification of M. tuberculosis complex organisms in 4 h and/or as a rapid screening method for the direct detection of M. tuberculosis complex organisms in specimens.

Use of DNA amplification for the rapid identification of Mycobacterium bovis

DNA amplification using the polymerase chain reaction technique was evaluated for rapid identification of Mycobacterium bovis. Two oligonucleotide primers of 20 bases in length were constructed to target a region of the gene encoding the M. bovis secretory protein, MPB70. The amplification reaction produced a single product 372 bp in size which was readily detected by agarose gel electrophoresis. All 84 strains of M. bovis tested produced a positive signal in the amplification reaction. In addition all isolates fro the M. tuberculosis complex tested, with the exception of M. microti, gave a single band at 372 bp. No amplified product was detected when 24 other species of mycobacteria and species from four other genera were tested. The sensitivity of the test was such that a single viable cell could be detected in the reaction. This technique provides a simple and extremely sensitive method of identifying isolates of M. bovis and other pathogenic M. tuberculosis complex organisms.

Evaluation of a new biphasic culture system for the recovery of mycobacteria

A newly developed biphasic culture system (MB-Check) for recovery of mycobacteria was evaluated. The biphasic system consists of a bottle containing selective modified Middlebrook 7H9 broth and a mounted dip slide with chocolate agar and modified Middlebrook 7H11 agar with and without NAP. The system was compared with culture on two egg-based media, Lowenstein medium and a selective Gottsacker medium, using 995 routine specimens and 90 artificially seeded sputa. Mycobacterium tuberculosis was detected in 17 of the 995 routine specimens by the biphasic system and in 14 specimens by the egg-based media together. In the artificially seeded sputa the biphasic system showed higher sensitivity in detection of both tuberculosis complex and non-tuberculous mycobacteria than the egg-based media. The recovery times of the new system were comparable to those of the two conventional culture methods.

Comparison of improved BACTEC and Lowenstein-Jensen media for culture of mycobacteria from clinical specimens

A 4-month trial involving 2,563 routine clinical specimens was conducted to compare the improved BACTEC TB system (12B medium) with the conventional Lowenstein-Jensen (LJ) media for the isolation, identification, and susceptibility testing of mycobacteria. One hundred sixty-two mycobacterial isolates were recovered, 147 (91%) with BACTEC and 118 (73%) with LJ media. Of these, 62 were Mycobacterium tuberculosis complex strains, 59 (95%) of which were isolated with BACTEC and 54 (87%) of which were isolated with LJ media. Of the remaining 100 isolates, which were mycobacteria other than tuberculosis (MOTT), BACTEC and LJ media detected 88 and 64%, respectively. The contamination rate was significantly higher in BACTEC (5%) than in LJ media (3.3%). The mean isolation time for M. tuberculosis complex with BACTEC was 15.5 days, compared with 25.6 days with LJ. For MOTT, the mean isolation times were 5.8 and 21.4 days, respectively. Identification of 32 M. tuberculosis complex isolates and 38 isolates of MOTT by the BACTEC NAP (p-nitro-alpha-acetylamino-beta-hydroxypropiophenone) inhibition test gave 100% agreement with conventional biochemical identifications. The results of susceptibility testing of 18 M. tuberculosis complex isolates with BACTEC agreed completely with those obtained by the resistance ratio method.

Rapid radiometric detection of mycobacterial growth from smear-positive tissue samples from pigs

Rapid demonstration of mycobacteria in slaughter pigs is important for medical, epidemiological and economic reasons. The Bactec radiometric system detected more mycobacteria in less time than conventional culture on solid medium.

Rapid detection and identification of pathogenic mycobacteria by combining radiometric and nucleic acid probe methods

The combination of radiometric methodology (BACTEC 12B) and probe technology for recovery and identification of mycobacteria was studied in two large hospital laboratories. The sediment from vials with positive growth indices was tested with DNA probes specific for Mycobacterium tuberculosis, Mycobacterium avium, and Mycobacterium intracellulare. The sensitivity of the radiometric method and the specificity of the probes resulted in a marked reduction in the time to the final report. Biochemical testing could be eliminated on isolates giving a positive reaction with one of the probes. Some 176 isolates of M. tuberculosis, 110 of M. avium, and 5 of M. intracellulare were recovered. Two-thirds of these isolates were detected and identified within 2 weeks of inoculation and the remainder was detected by 4 weeks, a reduction of 5 to 7 weeks to the final report.

Improved detection of Mycobacterium avium complex with the Bactec radiometric system

A reconsideration of the laboratory methods used for primary isolation of mycobacteria other than Mycobacterium tuberculosis is needed due to the increasingly recognized importance of such mycobacterial infections in immunocompromised patients. One example of this is the severe opportunistic infections caused by Mycobacterium avium complex among AIDS patients. In this study, the Bactec radiometric system was compared to conventional culture on solid medium for the detection of M. avium complex in 3,612 selected clinical specimens, mainly of extrapulmonary origin. Of a total number of 63 M. avium complex isolates, the Bactec system detected 58 (92%), compared to 37 (59%) for conventional culture. A much more rapid detection was attained with radiometric technique than with conventional culture. The mean detection time for the cultures positive with both methods was 7.1 and 28.3 days, respectively. The Bactec radiometric system achieves a rapid and significantly more sensitive detection and seems to be an excellent complement to conventional culture in the laboratory diagnosis of infections with the M. avium complex.

Laboratory diagnosis of mycobacterial infections in patients with acquired immunodeficiency syndrome

Disseminated mycobacterial infections are commonly seen in acquired immunodeficiency syndrome (AIDS) patients, and laboratory culture is the best method for diagnosing these infections. In addition to conventional agar media, we used BACTEC 12A (Johnston Laboratories, Inc., Towson, Md.) broth medium for culture. More isolates of Mycobacterium avium complex and Mycobacterium tuberculosis were recovered from 12A broth than from Lowenstein-Jensen or Middlebrook 7H11 agar. Also, the average detection time of these mycobacteria was the earliest with 12A broth. Stool examination has been helpful in diagnosing mycobacterial disease in AIDS patients, and in this study both acid-fast stain and culture of fecal material was necessary for efficient detection of mycobacteria. Another sensitive and practical method for detecting mycobacterial infections in patients with AIDS is the Isolator lysis-centrifugation system (Du Pont Co., Wilmington, Del.) which offers the advantage of quantitating the degree of mycobacteremia. Laboratories should be alerted to the possibility of mixed mycobacterial infection in patients with AIDS, and positive cultures should be repeatedly examined to detect coinfection with a slower-growing mycobacterium such as M. tuberculosis as well as M. avium complex.

Improved detection times for Mycobacterium avium complex and Mycobacterium tuberculosis with the BACTEC radiometric system

A total of 2,559 routine clinical specimens were cultured for mycobacteria by using BACTEC Middlebrook 7H12 medium (BACTEC), Lowenstein-Jensen slants (LJ), and Mycobactosel selective Middlebrook 7H11 slants (M7H11). Thirty-three isolates (1.3%) of M. avium complex and 82 isolates (3.2%) of M. tuberculosis were recovered. The BACTEC mean detection time of M. avium complex from 27 smear-negative specimens was earlier than that of conventional media for both decontaminated respiratory specimens (BACTEC, 12 days; LJ, 32 days; and M7H11, 38 days) and untreated tissue and fluid specimens (BACTEC, 8 days; LJ, 30 days; and M7H11, 31 days). The sensitivity for smear-negative M. avium complex with BACTEC (74%) was comparable to that with LJ (74%) and M7H11 (63%). The mean detection times of M. tuberculosis from 56 smear-positive respiratory specimens were 8 days for BACTEC, 16 days for LJ, and 17 days for M7H11, and sensitivities for the detection of positive cultures were 98% for BACTEC, 76% for LJ, and 79% for M7H11. The BACTEC mean detection time of M. tuberculosis in smear-negative specimens was better for tissues and fluids (14 days) than for respiratory specimens (24 days). BACTEC yielded substantially earlier detection of M. avium complex from all specimen types and of M. tuberculosis from smear-positive respiratory specimens. The rapid identification and susceptibility testing of M. tuberculosis in BACTEC agreed completely with conventional tests and provided a 3-week reduction in median time to final reports.

Rapid methods in clinical microbiology. Clinical situations in which rapid methods may best be applied

Utilization of rapid microbiologic methods could improve both the quality of patient care and help to reduce patient health care costs through more efficient patient management. Medically urgent situations such as meningitis, endocarditis, bacteremia, some soft tissue infections, ocular infections, and pneumonia in immunocompromised hosts are obvious areas for application of rapid methods. However, efficient management of outpatient infections such as group A streptococcal pharyngitis, bacteriuria, diarrhea, and sexually transmitted diseases could also benefit from rapid test results. Rapid methods for detection of slow growing or unculturable microorganisms represent a promising area for development of new test methodologies. Realization of the potential of various rapid microbiology tests, however, requires that several difficult questions be addressed. Acceptable test rapidity and accuracy must be established by concensus of microbiologists and clinicians. Moreover, new approaches to reduce total test turn-around time and novel means to facilitate physician use of rapid test results must be sought in the immediate future.