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.

Bone marrow cultures for the diagnosis of mycobacterial and fungal infections in patients infected with the human immunodeficiency virus

SETTING

University medical center.

OBJECTIVE

To determine the value of bone marrow cultures for mycobacteria and fungi in patients infected with the human immunodeficiency virus (HIV).

DESIGN

Retrospective review of charts and laboratory records.

RESULTS

From 1992-1996, 1225 bone marrow specimens were submitted for mycobacterial and fungal cultures. The number of specimens submitted,declined sharply from 435 in 1992 to 94 in 1996 (P = 0.002 for trend). The yield remained stable. Thirty-one of 1225 specimens grew mycobacteria or fungi; 26 isolates were from 24 HIV-infected patients. These 24 patients were infected with Mycobacterium avium complex (19), M. tuberculosis (one), M. chelonae (one), Histoplasma capsulatum (two), and Cryptococcus neoformans (one). All 24 HIV-infected patients had a culture submitted from at least one other site within 4 weeks of the positive bone marrow culture. The identical organism was grown from another site (usually blood) in 18 of these 24 patients. The bone marrow culture provided the only positive result in six patients and the first positive result in eight patients.

CONCLUSIONS

Utilization of bone marrow cultures for mycobacteria and fungi declined at our institution. Bone marrow and blood cultures were highly concordant. However, the majority of positive bone marrow cultures provided useful information.

Mycobacterium tusciae sp. nov

A new, slow-growing, scotochromogenic mycobacterium was isolated from a lymph node of an immunocompromised child and subsequently from tap water and from a respiratory specimen of a patient with chronic fibrosis. Alcohol-acid-fastness, lipid patterns and the G + C content clearly support the placement of this organism in the genus Mycobacterium. The isolates grew very slowly at temperatures ranging from 25 to 32 degrees C and showed activities of nitrate reductase, catalase, urease, arylsulfatase and Tween 80 hydrolysis. The organism was susceptible to all antimycobacterial drugs tested. The 16S rDNA sequence was unique and phylogenetic analysis placed the organism close to fast-growing species such as Mycobacterium farcinogenes, Mycobacterium komossense and Mycobacterium aichiense. These data support the conclusion that the isolates represent a new mycobacterial species, for which the name Mycobacterium tusciae sp. nov. is proposed. The type strain is strain FI-25796T; a culture of this strain has been deposited in the DSMZ as strain DSM 44338T.

Mycobacterium wolinskyi sp. nov. and Mycobacterium goodii sp. nov., two new rapidly growing species related to Mycobacterium smegmatis and associated with human wound infections: a cooperative study from the International Working Group on Mycobacterial Taxonomy

Previous investigations demonstrated three taxonomic groups among 22 clinical isolates of Mycobacterium smegmatis. These studies were expanded to 71 clinical isolates, of which 35 (49%) (group 1) were identical to five ATCC reference strains including the type strain ATCC 19420T. Twenty-eight isolates (39%) were group 2, and eight isolates (11%) were group 3. Isolates of groups 2 and 3 were most often associated with post-traumatic or post-surgical wound infections including osteomyelitis, were susceptible to sulfamethoxazole, amikacin, imipenem and the tetracyclines, variably resistant to clarithromycin, and susceptible (group 1), intermediately resistant (group 2) or resistant (group 3) to tobramycin. The three groups were similar by routine biochemical and growth characteristics, but had different mycolic acid dimethoxy-4-coumarinylmethyl ester elution patterns by HPLC and different PCR-restriction enzyme patterns of a 439 bp fragment of the hsp-65 gene. Group 3 isolates differed from group 1 by 18 bp by 16S rRNA sequencing and exhibited < 25% homology by DNA-DNA hybridization, being most closely related to Mycobacterium mageritense. The 16S rRNA of group 1 and group 2 isolates differed by only 3 bp, but by DNA-DNA hybridization they exhibited only 40% homology. The following names are proposed: Mycobacterium goodii sp. nov. for group 2 isolates (type strain ATCC 700504T = MO69T), Mycobacterium wolinskyi sp. nov. for group 3 isolates (type strain ATCC 700010T = MO739T) and Mycobacterium smegmatis sensu stricto for group 1 isolates.

Use of PCR-restriction fragment length polymorphism analysis of the hsp65 gene for rapid identification of mycobacteria in Brazil

Polymerase chain reaction amplification of part of the gene coding for the heat shock protein hsp65 followed by restriction enzyme analysis (PRA) is a recently described tool for rapid identification of mycobacteria. In this study, the speed and simplicity of PRA for identification of isolates of mycobacteria from patients with clinical symptoms of tuberculosis was evaluated and compared with identification results obtained by commercially available methods. Established PRA patterns were observed for nineteen isolates of Mycobacterium tuberculosis, eleven belonging to the complex M. avium-intracellulare, four of M. kansasii, one of M. fortuitum, one of M. abscessus, three of M. gordonae and one of the recently described species M. lentiflavum, as identified by commercially available methods. Two isolates of M. fortuitum and one of M. gordonae had unique and so far undescribed PRA patterns, suggesting geographically-related intra-species variation within the hsp65 sequence. We propose the inclusion of these new patterns in the PRA identification algorithm and have defined more accurately the molecular weight values of the restriction fragments. This is the first report on the isolation of M. lentiflavum in Brazil suggesting that identification by means of PRA could be useful for detection of mycobacterial species that are usually unnoticed. Where the use of several commercial techniques in combination was necessary for correct identification, PRA demonstrated to be a simple technique with good cost-benefit for characterization of all mycobacterial isolates in this study.

Defining the requirements for immunological control of mycobacterial infections

Tuberculosis remains a major public health problem throughout the world. Research into the immunological basis of the host-pathogen relationship has recently benefited from the fascinating convergence of genetic data from mouse models and from humans. Latency - the seemingly quiescent phase of bacterial persistence - is the central problem in controlling tuberculosis and will be the next frontier of research.

Mucosa-associated lymphoid tissues as sites for uptake, carriage and excretion of tubercle bacilli and other pathogenic mycobacteria

Pathogenic mycobacteria, including those that cause tuberculosis and paratuberculosis, cross mucosal barriers by endocytosis within mucosal lymphoepithelial sites. These entry sites commonly include oropharyngeal and nasopharyngeal tonsils and Peyer's patches. Bacilli discharged at the basolateral surfaces of engulfing epithelial M cells are taken up by professional antigen-presenting cells associated with T lymphocytes of the parafollicular area. Dendritic cells and macrophages in these sites allow mycobacterial replication, due to the permissive immunological environment in lymphoepithelial tissues. Abrogation of local delayed-type hypersensitivity reactions generally ensures continuing integrity and function of these tissues. Phagocytes containing intracellular mycobacteria disseminate infection to other parts of the body and also probably migrate back onto the mucosal surface to shed bacilli.

Identification of mycobacterial DNA in cutaneous lesions of sarcoidosis

Sarcoidosis is a multisystemic granulomatous disease of uncertain etiology. Recently, mycobacterial DNA especially Mycobacterium tuberculosis and Mycobacterium avium complex were detected in lung tissue and bronchial lavage fluid from patients with sarcoidosis by polymerase chain reaction (PCR) assays in 30% to 50% cases. Moreover, cell wall-defective form (CWDF) acid-fast bacteria have been isolated from skin lesions of patients with sarcoidosis which were later confirmed as M. avium complex by PCR assays. CWDF acid-fast bacteria were also found to grow from the blood of 95% patients with active sarcoidosis demonstrating a mycobacterial origin similar to M. tuberculosis. In view of these reports, we investigated 20 cases of cutaneous sarcoidosis using PCR/restriction enzyme pattern analysis (PCR/REPA) to detect mycobacterial DNA from paraffin-embedded skin biopsy samples. The method involves restriction enzyme analysis of nested PCR products obtained with primers encoding for the 65-KDa protein common to all mycobacteria. Using three restriction enzymes, the mycobacterial DNA from PCR product was differentiated to the species level. All the 20 cases had clinical and histologic evidence of sarcoidosis. Special stains for fungi (PAS) and mycobacteria (Fite) were negative and no foreign body was identified on polaroscopic examination in any of the cases. The cell lysates of M. tuberculosis, Mycobacterium bovis, Mycobacterium avium-intracellulare, Mycobacterium kansasii and Mycobacterium marinum from Centers for Disease Control (CDC) were used as standard control for PCR/REPA. Eight cases of foreign body granuloma, seven normal skin samples from the margin of surgical excisions and 5 cases of dermatitis were used as negative controls, and 4 cases of cutaneous tuberculosis were used as positive controls. Mycobacterial DNA was detected by PCR in 16 of the 20 cases of sarcoidosis. PCR/REPA subtyped 8 of these to M. tuberculosis complex (2 cases), M. avium-intracellulare (4 cases), M. kansasii (2 cases) while the other 8 cases were non-tuberculous mycobacteria. All four cases of cutaneous tuberculosis were positive by PCR and had a typical M. tuberculosis PCR/REPA pattern. Mycobacterial DNA was not detected in any of the negative controls. Our results demonstrated that mycobacterial DNA is present in 80% of cutaneous lesions of sarcoidosis and these mycobacteria may play a role in the pathogenesis of sarcoidosis.

The role of tissue studies in facilitating early initiation of antimycobacterial treatment in AIDS patients with disseminated mycobacterial disease

SETTING

The question of whether aggressive investigations are useful in diagnosis and initiation of treatment in AIDS patients with disseminated mycobacterial disease (DMD) is still under debate.

OBJECTIVE

To define the role of tissue studies in facilitating early initiation of antimycobacterial treatment and in establishing diagnosis in AIDS patients with DMD.

DESIGN

From July 1994 through June 1997, 167 AIDS cases with fever were evaluated by stepwise investigation using a standardized protocol. Data of DMD cases were analyzed to define the role of tissue studies.

RESULTS

A total of 40 cases of culture-proven DMD were identified. Antimycobacterial treatment was initiated due to positive acid-fast bacilli smears of sputum in only five cases. In the remaining cases, positive pathologic findings from tissue biopsies (lymph node, bone marrow or liver) facilitated early initiation of treatment in 60% (21/35). In 50% of all cases (20/40), the diagnosis could not have been established if cultures of tissue biopsies had not been performed. Both the pathologic examinations and mycobacterial cultures from liver biopsies had positivity rates of more than 50% (53.8% and 69.2%, respectively).

CONCLUSIONS

Tissue studies were useful in facilitating early initiation of treatment and establishing diagnosis at least in half of the AIDS cases with DMD. Liver biopsy is worthwhile if the cause of fever is not discovered using less invasive investigations.

Evaluation of the new MB redox system for detection of growth of mycobacteria

We evaluated a new mycobacterial culture system, MB Redox, for recovery rate and time to detection of mycobacteria from 742 consecutive respiratory specimens and compared the results to those found with Löwenstein-Jensen (LJ) medium. Twenty specimens (2.7%) were positive for M. tuberculosis: 17 on LJ medium and 19 in MB Redox, with 16 specimens positive in both media. In addition, 24 specimens (3.2%) were positive for nontuberculous mycobacteria (NTM), 20 on LJ medium, 18 in MB Redox, and 14 in both media. For M. tuberculosis, the mean times to detection were 28.9 days on LJ medium and 23.6 days in MB Redox, and for NTM, the mean times to detection were 40.6 days on LJ medium and 32.3 days in MB Redox.

Identification of mycobacterial species by comparative sequence analysis of the RNA polymerase gene (rpoB)

For the differentiation and identification of mycobacterial species, the rpoB gene, encoding the beta subunit of RNA polymerase, was investigated. rpoB DNAs (342 bp) were amplified from 44 reference strains of mycobacteria and clinical isolates (107 strains) by PCR. The nucleotide sequences were directly determined (306 bp) and aligned by using the multiple alignment algorithm in the MegAlign package (DNASTAR) and the MEGA program. A phylogenetic tree was constructed by the neighbor-joining method. Comparative sequence analysis of rpoB DNAs provided the basis for species differentiation within the genus Mycobacterium. Slowly and rapidly growing groups of mycobacteria were clearly separated, and each mycobacterial species was differentiated as a distinct entity in the phylogenetic tree. Pathogenic Mycobacterium kansasii was easily differentiated from nonpathogenic M. gastri; this differentiation cannot be achieved by using 16S rRNA gene (rDNA) sequences. By being grouped into species-specific clusters with low-level sequence divergence among strains of the same species, all of the clinical isolates could be easily identified. These results suggest that comparative sequence analysis of amplified rpoB DNAs can be used efficiently to identify clinical isolates of mycobacteria in parallel with traditional culture methods and as a supplement to 16S rDNA gene analysis. Furthermore, in the case of M. tuberculosis, rifampin resistance can be simultaneously determined.

Early identification of Mycobacterium tuberculosis and Mycobacterium avium using the polymerase chain reaction on samples positive by a rapid commercial culture system

A combination of two methods -- a rapid culture method [Mycobacteria Growth Indicator Tube (MGIT); Becton-Dickinson, USA] and a double polymerase chain reaction (PCR) assay -- was assessed for the detection and identification of Mycobacterium tuberculosis and Mycobacterium avium from clinical samples. The aim of the study was to evaluate the ability of the system to offer rapid and accurate diagnosis of mycobacterial infections. After decontamination, clinical samples (n = 554) were stained and cultured in parallel on solid media and in MGITs following standard procedures. The performance of the two culture systems was compared. Positive MGITs were tested for the presence of Mycobacterium tuberculosis and Mycobacterium avium by PCR of IS6110 (Mycobacterium tuberculosis) and the 16S rRNA gene (Mycobacterium avium). A total of 41 mycobacteria -- 27 Mycobacterium tuberculosis isolates, eight Mycobacterium avium isolates, and six other species of mycobacteria -- were isolated by one or both culture media. The MGIT system recovered 36 (87.8%) mycobacteria and the solid media 33 (80.4%). The mean time to detection by the two culture systems did not differ overall, but the mean time to detection of Mycobacterium avium from smear-positive specimens was shorter in MGITs than in solid media (5.25 days vs. 16.25 days, P < 0.05). The double PCR assay performed on the 36 positive MGITs correctly identified all 24 Mycobacterium tuberculosis-positive MGITs and all six Mycobacterium avium-positive vials. Therefore, application of the PCR assay to positive MGITs may mean that Mycobacterium tuberculosis and Mycobacterium avium can be identified at an earlier stage than with current methods.

Blood and charcoal added to acidified agar media promote the growth of Mycobacterium genavense

Ten different agar media were tested for the in vitro growth of Mycobacterium genavense in primary cultures and in subcultures from BACTEC vials. These agar media were based on Middlebrook 7H9, 7H10 and 7H11, and supplemented with additives: mycobactin J, yeast extract, charcoal, or defibrinated sheep blood. Some media were acidified with phosphoric acid to a final pH of 6.2 +/- 0.2. Fourteen M. genavense strains from nude mouse organs as well as one decontaminated clinical specimen (from a bird) were tested. The optimal medium for primary cultures of M. genavense was Middlebrook 7H11 acidified to pH 6.2 +/- 0.2 and supplemented with charcoal and sheep blood: on this medium, all strains produced colonies within 6-12 weeks of incubation in numbers approaching the number of bacilli inoculated. It was also the only medium to support the growth of the decontaminated clinical specimen. Added blood and charcoal appeared not as essential for subcultures as for primary cultures. Three media supported the growth of all strains within 1 month incubation: they were acidified, and were supplemented with yeast extract or pancreatic digest of casein, and with either blood or charcoal.

[Antimycobacterial antigens in lung secretion]

A latex antibody diagnostic kit was used to reveal microbacterial antigens in the sputum of patients with tuberculous and nonspecific lung disease in 54 and 38% of cases, respectively. It is suggested that Mycobacterium antigens are present in different tissues of an infected macroorganism.

Differential avian and human tuberculin skin testing in non-tuberculous mycobacterial infection

OBJECTIVE

To determine the sensitivity of differential avian and human delayed-type hypersensitivity skin testing in the diagnosis of non-tuberculous mycobacterial lymphadenitis.

METHOD

Retrospective review of all patients with culture proved non-tuberculous mycobacterial lymph node infections who also had differential avian and human skin testing performed over a 10 year period from 1986 to 1996.

RESULTS

One hundred and twenty four patients had non-tuberculous mycobacteria isolated from lymph nodes over this period, 59 of whom had differential skin testing performed. The sensitivity of a response of >/= 10 mm to the avian precipitin was 58 of 59. No patient had both a negative human and avian Mantoux. The sensitivity of the human Mantoux alone for diagnosing non-tuberculous mycobacterial infection was 81% for a response of >/= 5 mm and 66% for >/= 10 mm. Ten patients had a 0 human response. Fifty five of the 59 patients had an avian response at least 2 mm greater than the human response.

CONCLUSION

The avian Mantoux is a very sensitive method of diagnosing non-tuberculous mycobacterial infection in children. The human Mantoux is not sensitive enough to be used alone as a surrogate to diagnose non-tuberculous mycobacterial infection.

Central line sepsis in a child due to a previously unidentified mycobacterium

A rapidly growing mycobacterium similar to strains in the present Mycobacterium fortuitum complex (M. fortuitum, M. peregrinum, and M. fortuitum third biovariant complex [sorbitol positive and sorbitol negative]) was isolated from a surgically placed central venous catheter tip and three cultures of blood from a 2-year-old child diagnosed with metastatic hepatoblastoma. The organism's unique phenotypic profile and ribotype patterns differed from those of the type and reference strains of the M. fortuitum complex and indicate that this organism may represent a new pathogenic taxon.

Simple and rapid identification of different species of Mycobacteria by PCR

A simple polymerase chain reaction (PCR) assay for rapid identification of different species of mycobacteria was developed. This PCR is based on the use of conserved sequences to amplify the genome of several mycobacterial species. The amplification patterns obtained were specific and reproducible for the species tested. In particular, we could identify Mycobacterium tuberculosis and Mycobacterium bovis (both produced the same pattern), Mycobacterium avium, Mycobacterium kansasii, Mycobacterium xenopi, Mycobacterium chelonae, Mycobacterium peregrinum, Mycobacterium fortuitum, Mycobacterium gordonae and Mycobacterium smegmatis. Moreover, due to the numerous copies of the target sequences present in the genome, the PCR showed a very high level of sensitivity.

Gas chromatographic assay of cellular fatty acids and alcohols for the identification of Mycobacterium species

Ten mycobacterial species obtained from 141 cultures isolated from clinical specimens were studied. The cultures were grown on solid medium and then analysed-after saponification, methylation, extraction with organic solvent and washing of the organic phase--by capillary gas-liquid chromatography for fatty acid and secondary alcohol composition. The absence of secondary alcohols was characteristic of M. genavense, M. tuberculosis and the following Mycobacterium species with specific branched-chain fatty acids allowing their direct identification: M. gordonae, M. kansasii and M. marinum. The presence of secondary alcohols was characteristic of M. avium, M. phlei, M. scrofulaceum, M. terrae and M. xenopi. In the case of M. xenopi direct identification was made possible by the presence of a specific alcohol.

Systemic mycobacterioses in AIDS patients as determined by blood cultures on biphasic medium

Bacteremia due to mycobacteria can occur in AIDS patients in whom a rapid diagnosis is extremely important in order to plan a therapeutic conduct. Blood culture of mycobacteria using a biphasic system was set up in the Regional Laboratories of the Adolfo Lutz Institute, SP (Campinas, Ribeirão Preto, Santo André, Santos, São José do Rio Preto and Sorocaba). During a three year period (1994-97), 1521 blood samples were analyzed from 1336 AIDS patients, with CD4+ cell count < 100/ml, hematocrit < 30% and serum albumin concentration < 3.0 g/dl seen in regional outpatient clinics or as inpatients in hospitals. Of the blood samples examined, 9.9% were positive for mycobacteria. The predominant species was Mycobacterium avium complex (MAC) (53.8%) followed by Mycobacterium tuberculosis (28.0%). Mycobacterium xenopi was isolated in one case (0.8%) and in the remaining 17.4% the mycobacteria isolated were not identified. The implementation of blood culture for mycobacteria in our Institute has permitted the laboratory diagnosis of mycobacterial infections, in addition to providing data on the frequency of disseminated mycobacterial disease in AIDS patients in the region.

Macrophages are a significant source of type 1 cytokines during mycobacterial infection

T-helper 1 (Th1) cells are believed to be the major producer of the type 1 cytokine interferon-gamma (IFN-gamma) in cell-mediated immunity against intracellular infection. We have investigated the ability of macrophages to release type 1 cytokines and their regulatory mechanisms using both in vivo and in vitro models of pulmonary mycobacterial infection. During pulmonary infection by live Mycobacterium bovis bacilli Calmette-Guérin (BCG) in wild-type mice, lung macrophages released interleukin-12 (IL-12), IFN-gamma, and tumor necrosis factor-alpha (TNF-alpha), and expressed surface activation markers. However, macrophages in infected IL-12(-/-) mice released TNF-alpha but not IFN-gamma and lacked surface activation makers. In freshly isolated lung macrophages from naive IL-2(-/-) mice, mycobacteria alone released TNF-alpha but not IFN-gamma, whereas exogenously added IL-12 alone released a minimum of IFN-gamma. However, these macrophages released large quantities of IFN-gamma upon stimulation with both mycobacteria and IL-12. In contrast, mycobacteria and exogenous IFN-gamma released only a minimum of endogenous IFN-gamma. Endogenous IL-18 (IFN-gamma-inducing factor) played little role in IFN-gamma responses by macrophages stimulated by mycobacteria and IL-12. Our data reveal that macrophages are a significant source of type 1 cytokines during mycobacterial infection and that both IL-12 and intracellular pathogens are required for the release of IFN-gamma but not TNF-alpha. These findings suggest that macrophages regulate cell-mediated immunity by releasing not only IL-12 and TNF-alpha but also IFN-gamma and that full activation of IFN-gamma response in macrophages is tightly regulated.

Use of restriction enzyme analysis of amplified DNA coding for the hsp65 gene and polymerase chain reaction with universal primer for rapid differentiation of mycobacterium species in the clinical laboratory

Two rapid procedures, restriction enzyme analysis of the amplified segment of the gene encoding for the 65000 mol. wt heat shock protein and a polymerase chain reaction with single universal primer (UP-PCR), were used for the identification of Mycobacterium tuberculosis complex (n = 47) and proving the species identity of non-tuberculous mycobacteria (NTM, n=36) cultured from clinical samples by comparing the resulting DNA banding pattern with patterns derived from mycobacterial type strains (n = 24). UP-PCR assay provided a rather wide limit of tolerance for variations in procedure. Although mycobacterial strains were found to generate species-specific banding patterns in both assays, M. tuberculosis and M. bovis strains and isolates produced nearly the same DNA patterns, which were very distinctive from that of all NTM tested. Investigation of the majority of M. fortuitum (n = 14) and M. kansasii (n = 7), mycobacteria most frequently causing mycobacterioses in the region, as well as other NTM isolates, showed reproducible patterns characteristic of corresponding type strains. Both methods combine the advantages of ordinary PCR and PCR 'fingerprinting', namely, the species-specific DNA pattern and primers applicable to different species. They may be applied as rapid tests for proving the identity of Mycobacterium species in a clinical laboratory.