No abstract

Contamination of broth cultures of acid-fast bacilli (AFB) by bacterial species other thanMycobacterium species frequently occurs. Many of these contaminated cultures require redecontamination and reincubation before the appropriate tests can be performed for identification, significantly affecting the turnaround time for reporting culture results. In this study, the Amplified Mycobacterium Tuberculosis Direct Test (MTD; GenProbe) was performed to detect the Mycobacterium tuberculosis complex (MTBC) in 125 BACTEC 12B broth cultures with positive growth indices. Among these, 41 grew non-AFB bacteria only, and all 41 were negative by the MTD. The remaining 84 bottles contained contaminated cultures that grew both AFB and other bacteria or yeasts. Repeat decontamination and reincubation of these specimens required a mean time of 13 days (range, 3 to 40 days). The MTD results were positive for 10 samples, 9 of which were MTBC culture positive and 1 of which grew Myobacterium celatum, a species known to cross-react in the MTD. All cultures growing other mycobacterial species were negative by the MTD. The results of this study demonstrate that the MTD is both sensitive and specific in detecting MTBC in contaminated broth cultures and that, when used selectively, the MTD can potentially rule in or out a diagnosis of MTBC as much as 12 days earlier than using nonamplified DNA probe testing alone can.Tuberculosis remains a major cause of morbidity and mortality worldwide. Rapid and accurate detection of the Mycobacterium tuberculosis complex (MTBC) is a key aspect of effective tuberculosis treatment and control. Although the recently introduced nucleic acid amplification tests provide an opportunity for the early diagnosis of disease, routine culture of acid-fast bacilli (AFB) is still necessary for its higher sensitivity and ability to identify mycobacterial species other than MTBC and for the recovery of isolates for antimicrobial susceptibility testing. For the majority of specimens for AFB culture, modern culture techniques make it possible to meet the 21-day target turnaround time for detection and identification of MTBC as recommended by the Centers for Disease Control and Prevention (22). However, despite standardized techniques for decontamination and concentration and for the addition of antibiotics, contamination of broth cultures by bacteria other than AFB still occurs in 2 to greater than 10% of cultures (8,14,15,18,23,24,26). Many of these contaminated cultures grow AFB as well as other contaminating organisms, thus requiring a redecontamination step and reincubation before the appropriate tests (such as chromatographic or biochemical methods) can be performed for organism identification. The turnaround time for reporting culture results is thus significantly affected in this group of cultures. Although the use of DNA probes for detection and identification may be helpful in some of these contaminated cultures, such use is not specified in the manufacturer's instructions or discussed in published literature....