Frank G Witebsky

Publications of Frank G Witebsky

• Multisite Reproducibility of the Broth Microdilution Method for Susceptibility Testing of Nocardia species.

  Authors: Patricia S Conville, Barbara A Brown-Elliott, Richard J Wallace, Frank G Witebsky, Deloris Koziol, Geraldine S Hall, Scott B Killian, Cindy C Knapp, David Warshauer, Tam Van, Nancy L Wengenack, Sharon Deml, Gail L Woods

  Journal of clinical microbiology. 01/2012;

  Antimicrobial susceptibility testing (AST) of clinical isolates of Nocardia is recommended to detect resistance to commonly used antimicrobial agents; such testing is complicated by difficulties inAntimicrobial susceptibility testing (AST) of clinical isolates of Nocardia is recommended to detect resistance to commonly used antimicrobial agents; such testing is complicated by difficulties in inoculum preparation and test interpretation. In this study, six laboratories performed repetitive broth microdilution testing on single strains of Nocardia brasiliensis, Nocardia cyriacigeorgica, Nocardia farcinica, Nocardia nova and Nocardia wallacei. For each isolate, a total of 30 microdilution panels from three different lots were tested at most sites. The goal of the study was to determine the inter- and intra-laboratory reproducibility of susceptibility testing of this group of isolates. Acceptable agreement [> 90% agreement at (±) 1 dilution of the minimum inhibitory concentration (MIC) mode] was found for amikacin, ciprofloxacin, clarithromycin and moxifloxacin. After eliminating MIC values from single laboratories whose results showed the greatest deviation from those of the remaining laboratories, acceptable agreement was also found for amoxicillin/clavulanic acid, linezolid, minocycline and tobramycin. Results showed unsatisfactory reproducibility of broth microdilution testing of ceftriaxone with N. cyriacigeorgica and N. wallacei, tigecycline with N. brasiliensis and N. cyriacigeorgica and sulfonamides with N. farcinica and N. wallacei. N. nova ATCC BAA-2227 is proposed as a quality control organism for AST of Nocardia sp., and the use of a disk diffusion test for sulfisoxazole is proposed as a check of the adequacy of the inoculum and to confirm sulfonamide MIC results.

• M. tilburgii, a newly described, uncultivated opportunistic pathogen: Case report and review of the literature.

  Authors: Tara N. Palmore, Yvonne R Shea, Patricia S Conville, Frank G Witebsky, Victoria L Anderson, Irene P. Rupp Hodge, Steven M Holland

  Journal of clinical microbiology. 04/2009;

  Molecular methods are increasingly used to identify pathogens that are difficult to cultivate. We report a case of disseminated infection with Mycobacterium tilburgii, a proposed species that hasMolecular methods are increasingly used to identify pathogens that are difficult to cultivate. We report a case of disseminated infection with Mycobacterium tilburgii, a proposed species that has never been cultivated. The case illustrates the diagnostic utility of sequence analysis of the 16S rRNA gene directly from the clinical specimen.

• Nocardia cyriacigeorgica--an established rather than an emerging pathogen.

  Authors: Frank G Witebsky, Patricia S Conville, Richard J Wallace, Barbara A Brown-Elliott, Richard C Huard, Robert Schlaberg, Phyllis Della-Latta

  Journal of clinical microbiology. 08/2008; 46(7):2469; author reply 2469-70.

• Nocardia wallacei sp. nov. and Nocardia blacklockiae sp. nov., human pathogens and members of the "Nocardia transvalensis Complex".

  Authors: Patricia S Conville, June M Brown, Arnold G Steigerwalt, Barbara A Brown-Elliott, Frank G Witebsky

  Journal of clinical microbiology. 05/2008; 46(4):1178-84.

  Nocardia isolates that share the property of in vitro amikacin resistance are grouped together by some authors in the Nocardia transvalensis complex. Our examination of 13 isolates that are amikacinNocardia isolates that share the property of in vitro amikacin resistance are grouped together by some authors in the Nocardia transvalensis complex. Our examination of 13 isolates that are amikacin resistant has revealed the existence of three distinct species. Sequence analysis of the 16S rRNA, 65-kDa heat shock protein, and secA1 genes, coupled with DNA-DNA hybridization, indicated that "N. asteroides drug pattern IV," "N. transvalensis new taxon 1," and N. transvalensis sensu stricto should each be considered a distinct species. The phenotypic and molecular characteristics of the proposed new species Nocardia wallacei (N. asteroides drug pattern IV) and N. blacklockiae (N. transvalensis new taxon 1) are presented and compared with those of N. transvalensis sensu stricto. The relative genetic diversity of isolates best placed with the species N. blacklockiae is also discussed. Case studies demonstrating the pathogenicity of N. wallacei and N. blacklockiae are presented. The type strain of N. wallacei is ATCC 49873 (DSM 45136), and that of N. blacklockiae is ATCC 700035 (DSM 45135).

• Fulminant mulch pneumonitis: an emergency presentation of chronic granulomatous disease.

  Authors: Sophia Siddiqui, Victoria L Anderson, Diane M Hilligoss, Mario Abinun, Taco W Kuijpers, Henry Masur, Frank G Witebsky, Yvonne R Shea, John I Gallin, Henry L Malech, Steven M Holland

  Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 10/2007; 45(6):673-81.

  BACKGROUND: Chronic granulomatous disease (CGD) is associated with multiple and recurrent infections. In patients with CGD, invasive pulmonary infection with Aspergillus species remains the greatestBACKGROUND: Chronic granulomatous disease (CGD) is associated with multiple and recurrent infections. In patients with CGD, invasive pulmonary infection with Aspergillus species remains the greatest cause of mortality and is typically insidious in onset. Acute fulminant presentations of fungal pneumonia are catastrophic. METHODS: Case records, radiograph findings, and microbiologic examination findings of patients with CGD who had acute presentations of dyspnea and diffuse pulmonary infiltrates caused by invasive fungal infection were reviewed and excerpted onto a standard format. RESULTS: From 1991 through 2004, 9 patients who either were known to have CGD or who received a subsequent diagnosis of CGD presented with fever and new onset dyspnea. Eight patients were hypoxic at presentation; bilateral pulmonary infiltrates were noted at presentation in 6 patients and developed within 2 days after initial symptoms in 2 patients. All patients received diagnoses of invasive filamentous fungi; 4 patients had specimens that also grew Streptomyces species on culture. All patients had been exposed to aerosolized mulch or organic material 1-10 days prior to the onset of symptoms. Cases did not occur in the winter. Five patients died. Two patients, 14 years of age and 23 years of age, who had no antecedent history of recognized immunodeficiency, were found to have p47(phox)-deficient CGD. CONCLUSIONS: Acute fulminant invasive fungal pneumonia in the absence of exogenous immunosuppression is a medical emergency that is highly associated with CGD. Correct diagnosis has important implications for immediate therapy, genetic counseling, and subsequent prophylaxis.

• Organisms designated as Nocardia asteroides drug pattern type VI are members of the species Nocardia cyriacigeorgica.

  Authors: Patricia S Conville, Frank G Witebsky

  Journal of clinical microbiology. 08/2007; 45(7):2257-9.

  Nocardia cyriacigeorgica has recently been described as an "emerging" pathogen. However, DNA-DNA hybridization results confirm that Nocardia asteroides drug pattern type VI, which has long beenNocardia cyriacigeorgica has recently been described as an "emerging" pathogen. However, DNA-DNA hybridization results confirm that Nocardia asteroides drug pattern type VI, which has long been recognized as a common and significant pathogen in the United States, belongs to the species N. cyriacigeorgica.

• Analysis of multiple differing copies of the 16S rRNA gene in five clinical isolates and three type strains of Nocardia species and implications for species assignment.

  Authors: Patricia S Conville, Frank G Witebsky

  Journal of clinical microbiology. 05/2007; 45(4):1146-51.

  Five clinical isolates of Nocardia that showed ambiguous bases within the variable region of the 16S rRNA gene sequence were evaluated for the presence of multiple copies of this gene. The typeFive clinical isolates of Nocardia that showed ambiguous bases within the variable region of the 16S rRNA gene sequence were evaluated for the presence of multiple copies of this gene. The type strains of three Nocardia species, Nocardia concava, Nocardia ignorata, and Nocardia yamanashiensis, which also showed ambiguous bases in the variable region, were also examined. Cloning experiments using an amplified region of the 16S rRNA that contains the variable region showed that each isolate possessed 16S rRNA genes with at least two different sequences. In addition, hybridization studies using a 16S rRNA gene-specific probe and extracted genomic DNA of the patient isolates and of the type strain of N. ignorata showed that each isolate possessed at least three copies of the gene. These multiple differing copies of the 16S rRNA gene and the results of DNA-DNA hybridization studies indicate problems of species definition and identification for such isolates. A broader species concept than that currently in vogue may be required to accommodate such organisms.

• Analysis of secA1 gene sequences for identification of Nocardia species.

  Authors: Patricia S Conville, Adrian M Zelazny, Frank G Witebsky

  Journal of clinical microbiology. 09/2006; 44(8):2760-6.

  Molecular methodologies, especially 16S rRNA gene sequence analysis, have allowed the recognition of many new species of Nocardia and to date have been the most precise methods for identifyingMolecular methodologies, especially 16S rRNA gene sequence analysis, have allowed the recognition of many new species of Nocardia and to date have been the most precise methods for identifying isolates reliably to the species level. We describe here a novel method for identifying Nocardia isolates by using sequence analysis of a portion of the secA1 gene. A region of the secA1 gene of 30 type or reference strains of Nocardia species was amplified using secA1-specific primers. Sequence analysis of 468 bp allowed clear differentiation of all species, with a range of interspecies similarity of 85.0% to 98.7%. Corresponding 16S rRNA gene sequences of a 1,285-bp region for the same isolates showed a range of interspecies similarity of 94.4 to 99.8%. In addition to the type and reference strains, a 468-bp fragment of the secA1 gene was sequenced from 40 clinical isolates of 12 Nocardia species previously identified by 16S rRNA gene sequence analysis. The secA1 gene sequences of most isolates showed >99.0% similarity to the secA1 sequences of the type or reference strain to which their identification corresponded, with a range of 95.3 to 100%. Comparison of the deduced 156 amino acid sequences of the SecA1 proteins of the clinical isolates showed between zero and two amino acid residue differences compared to that of the corresponding type or reference strain. Sequencing of the secA1 gene, and using deduced amino acid sequences of the SecA1 protein, may provide a more discriminative and precise method for the identification of Nocardia isolates than 16S rRNA gene sequencing.

• Multiple copies of the 16S rRNA gene in Nocardia nova isolates and implications for sequence-based identification procedures.

  Authors: Patricia S Conville, Frank G Witebsky

  Journal of clinical microbiology. 07/2005; 43(6):2881-5.

  Molecular investigation of two Nocardia patient isolates showed unusual restriction fragment length polymorphism patterns with restriction endonuclease assays (REA) using an amplified portion of theMolecular investigation of two Nocardia patient isolates showed unusual restriction fragment length polymorphism patterns with restriction endonuclease assays (REA) using an amplified portion of the 16S rRNA gene. Patterns typical of Nocardia nova were obtained with REA of an amplified portion of the 65-kDa heat shock protein gene. Subsequent sequence analysis of the 16S rRNA gene regions of these isolates showed the presence of ambiguous bases within an expected restriction endonuclease recognition site which were not able to be resolved on repeat testing. Cloning of amplified regions of the 16S rRNA genes and subsequent sequencing of the resulting clones from the two patient isolates showed three different 16S rRNA gene sequences which corresponded to sequences found in N. nova, a molecular variant of N. nova, and a previously undescribed sequence. Hybridization studies using a DNA probe corresponding to an 89-bp conserved region of the 16S rRNA gene confirmed the presence of at least two copies of the 16S rRNA gene in the N. nova type strain, in a patient isolate identical to the molecular variant of N. nova, and in the two other patient isolates. All isolates were found to belong to the species N. nova as determined by DNA-DNA hybridization. Because minimal variation has been found in the 16S rRNA gene sequences of different species of Nocardia, those laboratories employing molecular methods for identification of these species must be aware of the potential identification complications that may be caused by the presence of differing 16S rRNA genes in the same isolate.

• Nocardia kruczakiae sp. nov., a pathogen in immunocompromised patients and a member of the "N. nova complex".

  Authors: Patricia S Conville, June M Brown, Arnold G Steigerwalt, Judy W Lee, Victoria L Anderson, Joel T Fishbain, Steven M Holland, Frank G Witebsky

  Journal of clinical microbiology. 12/2004; 42(11):5139-45.

  Molecular methodologies have become useful techniques for the identification of pathogenic Nocardia species and for the recognition of novel species that are capable of causing human disease. TwoMolecular methodologies have become useful techniques for the identification of pathogenic Nocardia species and for the recognition of novel species that are capable of causing human disease. Two isolates recovered from immunocompromised patients were characterized as Nocardia nova by biochemical and susceptibility testing results. The restriction fragment length polymorphism (RFLP) patterns obtained by restriction endonuclease analysis (REA) of an amplified portion of the heat shock protein gene were identical to those obtained with the type strain of N. nova. REA of an amplified portion of the 16S rRNA gene showed RFLP patterns that were unlike those obtained for the type strain of N. nova but that were similar to those obtained for the type strains of N. africana and N. veterana. Subsequent sequencing of a portion of the 16S rRNA gene produced identical results for the two patient isolates. Sequence analysis of 1,352-bp portions of the 16S rRNA gene indicated that these isolates were 99.8% similar to the recently described species N. veterana but were only 99.3, 98.1, and 98.1% similar to the type strains of N. africana, N. nova, and N. vaccinii, respectively. DNA-DNA hybridization studies confirmed that the two patient isolates belonged to the same species but were not closely related to N. africana, N. nova, N. vaccinii, or N. veterana. The patient isolates have been designated N. kruczakiae sp. nov. Because N. africana, N. veterana, and the new species are not readily differentiated from N. nova by phenotypic methods alone, the designation "N. nova complex" can be used to designate isolates such as these that phenotypically resemble N. nova but that have not been definitively characterized by 16S rRNA gene sequencing or DNA-DNA hybridization.

• Evaluation of partial 16S ribosomal DNA sequencing for identification of nocardia species by using the MicroSeq 500 system with an expanded database.

  Authors: Joann L Cloud, Patricia S Conville, Ann Croft, Dag Harmsen, Frank G Witebsky, Karen C Carroll

  Journal of clinical microbiology. 03/2004; 42(2):578-84.

  Identification of clinically significant nocardiae to the species level is important in patient diagnosis and treatment. A study was performed to evaluate Nocardia species identification obtained byIdentification of clinically significant nocardiae to the species level is important in patient diagnosis and treatment. A study was performed to evaluate Nocardia species identification obtained by partial 16S ribosomal DNA (rDNA) sequencing by the MicroSeq 500 system with an expanded database. The expanded portion of the database was developed from partial 5' 16S rDNA sequences derived from 28 reference strains (from the American Type Culture Collection and the Japanese Collection of Microorganisms). The expanded MicroSeq 500 system was compared to (i). conventional identification obtained from a combination of growth characteristics with biochemical and drug susceptibility tests; (ii). molecular techniques involving restriction enzyme analysis (REA) of portions of the 16S rRNA and 65-kDa heat shock protein genes; and (iii). when necessary, sequencing of a 999-bp fragment of the 16S rRNA gene. An unknown isolate was identified as a particular species if the sequence obtained by partial 16S rDNA sequencing by the expanded MicroSeq 500 system was 99.0% similar to that of the reference strain. Ninety-four nocardiae representing 10 separate species were isolated from patient specimens and examined by using the three different methods. Sequencing of partial 16S rDNA by the expanded MicroSeq 500 system resulted in only 72% agreement with conventional methods for species identification and 90% agreement with the alternative molecular methods. Molecular methods for identification of Nocardia species provide more accurate and rapid results than the conventional methods using biochemical and susceptibility testing. With an expanded database, the MicroSeq 500 system for partial 16S rDNA was able to correctly identify the human pathogens N. brasiliensis, N. cyriacigeorgica, N. farcinica, N. nova, N. otitidiscaviarum, and N. veterana.

• Nocardia veterana as a pathogen in North American patients.

  Authors: Patricia S Conville, June M Brown, Arnold G Steigerwalt, Judy W Lee, Dorothy E Byrer, Victoria L Anderson, Susan E Dorman, Steven M Holland, Barbara Cahill, Karen C Carroll, Frank G Witebsky

  Journal of clinical microbiology. 07/2003; 41(6):2560-8.

  The molecular methodologies used in our laboratories have allowed us to define a group of Nocardia isolates from clinical samples which resemble the type strain of Nocardia veterana. Three patientThe molecular methodologies used in our laboratories have allowed us to define a group of Nocardia isolates from clinical samples which resemble the type strain of Nocardia veterana. Three patient isolates and the type strain of N. veterana gave identical and distinctive restriction fragment length polymorphisms (RFLPs) for an amplified portion of the 16S rRNA gene. These three isolates and the N. veterana type strain also gave identical RFLPs for an amplified portion of the 65-kDa heat shock protein gene, but this pattern was identical to that obtained for the Nocardia nova type strain. Sequence analysis of both a 1,359-bp region of the 16S rRNA gene and a 441-bp region of the heat shock protein gene of the patient isolates showed 100% identities with the same regions of the N. veterana type strain. DNA-DNA hybridization of the DNA of one of the patient isolates with the DNA of the N. veterana type strain showed a relative binding ratio of 82%, with 0% divergence, confirming that the isolate was N. veterana. Biochemical and susceptibility testing showed no significant differences among the patient isolates and the N. veterana type strain. Significantly, the results of antimicrobial susceptibility testing obtained for our isolates were similar to those obtained for N. nova, indicating that susceptibility testing alone cannot discriminate between these species. We present two case studies which show that N. veterana is a causative agent of pulmonary disease in immunocompromised patients residing in North America. We also describe difficulties encountered in using 16S rRNA gene sequences alone for discrimination of N. veterana from the related species Nocardia africana and N. nova because of the very high degree of 16S rRNA gene similarity among them.

• Laboratory diagnosis of invasive mycoses.

  Authors: Elizabeth M O'Shaughnessy, Yvonne M Shea, Frank G Witebsky

  Infectious disease clinics of North America. 04/2003; 17(1):135-58.

  Rising numbers of immunocompromised patients have led to an ever-increasing population at risk of invasive fungal disease. Much has been achieved in the laboratory diagnosis of these infections, suchRising numbers of immunocompromised patients have led to an ever-increasing population at risk of invasive fungal disease. Much has been achieved in the laboratory diagnosis of these infections, such as advances in blood culture systems, and the development of new biochemical, antigen detection assays, and molecular methodologies. More standardized susceptibility testing guidelines provide for better therapeutic interventions. In an era of economic cutbacks in health care, future challenges include the development of cost-effective and technically simplified systems, which provide early detection and identification of common and emerging fungal pathogens. It will, however, take some time to establish the clinical relevance of these new methodologies in different patient populations.

• Multisite reproducibility of results obtained by two broth dilution methods for susceptibility testing of Mycobacterium avium complex.

  Authors: Gail L Woods, Natalie Williams-Bouyer, Richard J Wallace, Barbara A Brown-Elliott, Frank G Witebsky, Patricia S Conville, Marianne Plaunt, Geraldine Hall, Priscilla Aralar, Clark Inderlied

  Journal of clinical microbiology. 02/2003; 41(2):627-31.

  A multicenter study was conducted to assess the interlaboratory reproducibility of susceptibility testing of Mycobacterium avium complex (MAC) by broth microdilution using two different mediaA multicenter study was conducted to assess the interlaboratory reproducibility of susceptibility testing of Mycobacterium avium complex (MAC) by broth microdilution using two different media (cation-adjusted Mueller-Hinton broth with 5% oleic acid-albumin-dextrose-catalase and 7H9 broth with casein) and by macrodilution using the BACTEC 460TB and 12B media at pH 6.8 and 7.3 to 7.4. Ten well-characterized strains of MAC (four macrolide susceptible, six macrolide resistant) were tested against clarithromycin and azithromycin (the latter only by BACTEC 460TB, pH 6.8). At each site, strains were tested against clarithromycin three times on each of three separate days (nine testing events per isolate) by using a common lot of microdilution trays and BACTEC 12B medium, pH 6.8; strains were tested once on three separate days against clarithromycin in 12B medium at pH 7.3 to 7.4 and against azithromycin. Agreement among MICs (i.e., mode +/- 1 twofold dilution) was 100% for all strains and both drugs when BACTEC 460TB was used, regardless of the pH of the medium, but varied when microdilution with either medium was used, particularly with susceptible strains. Agreement based on interpretive category, with NCCLS-recommended breakpoints, was 100% for all strains with the BACTEC 460TB method (both drugs and both pH values) and with microdilution using 7H9 broth. With microdilution and Mueller-Hinton broth, agreement by interpretive category was 100% for eight isolates and >90% for two; errors occurred only in laboratories where personnel had minimal experience with this technique. MAC susceptibility testing may be performed by broth macrodilution or microdilution at either pH, with NCCLS-recommended interpretive breakpoints. However, because visual interpretation of broth microdilution end points is subjective, it is more prone to reader error; therefore, this method requires greater expertise than the BACTEC 460TB. Both techniques require appropriate validation and continued documentation of proficiency.

• Large-scale screening of nasal swabs for Bacillus anthracis: descriptive summary and discussion of the National Institutes of Health's experience.

  Authors: Pattarachai Kiratisin, Caroline D Fukuda, Alexandra Wong, Frida Stock, Jeanne C Preuss, Laura Ediger, Trupti N Brahmbhatt, Steven H Fischer, Daniel P Fedorko, Frank G Witebsky, Vee J Gill

  Journal of clinical microbiology. 09/2002; 40(8):3012-6.

  In October 2001, a letter containing a large number of anthrax spores was sent through the Brentwood post office in Washington, D.C., to a United States Senate office on Capitol Hill, resulting inIn October 2001, a letter containing a large number of anthrax spores was sent through the Brentwood post office in Washington, D.C., to a United States Senate office on Capitol Hill, resulting in contamination in both places. Several thousand people who worked at these sites were screened for spore exposure by collecting nasal swab samples. We describe here a screening protocol which we, as a level A laboratory, used on very short notice to process a large number of specimens (3,936 swabs) in order to report preliminary results as quickly as possible. Six isolates from our screening met preliminary criteria for Bacillus anthracis identification and were referred for definitive testing. Although none of the isolates was later confirmed to be B. anthracis, we studied these isolates further to define their biochemical characteristics and 16S rRNA sequences. Four of the six isolates were identified as Bacillus megaterium, one was identified as Bacillus cereus, and one was an unidentifiable Bacillus sp. Our results suggest that large-scale nasal-swab screening for potential exposure to anthrax spores, particularly if not done immediately postexposure, may not be very effective for detecting B. anthracis but may detect a number of Bacillus spp. that are phenotypically very similar to B. anthracis.

• Nocardia infection in chronic granulomatous disease.

  Authors: Susan E Dorman, Shireen V Guide, Patricia S Conville, Ellen S DeCarlo, Harry L Malech, John I Gallin, Frank G Witebsky, Steven M Holland

  Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 09/2002; 35(4):390-4.

  To determine the clinical characteristics and outcome of Nocardia infection in patients with chronic granulomatous disease (CGD), we reviewed data on 28 episodes of Nocardia infection in 23 patientsTo determine the clinical characteristics and outcome of Nocardia infection in patients with chronic granulomatous disease (CGD), we reviewed data on 28 episodes of Nocardia infection in 23 patients with CGD. All episodes involved pulmonary infection. The frequency of disseminated nocardiosis was 25% for the case series overall, but it was 56% among episodes in patients receiving neither interferon-gamma (IFN-gamma) nor sulfonamide prophylaxis. Patients receiving prophylaxis with IFN-gamma and/or a sulfonamide were significantly less likely to have disseminated nocardiosis than were patients not receiving these medications, and no patient receiving both medications developed disseminated nocardiosis. One-third of the patients had concomitant fungal infections, and 2 patients had concomitant Legionella infections. The majority of patients were successfully treated with a sulfonamide-containing regimen, even though some patients had developed Nocardia infection while receiving sulfonamide prophylaxis. Nocardia infections in patients with CGD are not usually fatal if treated properly, and prophylaxis with IFN-gamma and a sulfonamide may protect against dissemination.

• Comparison of three techniques for concentrating positive BACTEC 13A bottles for mycobacterial DNA probe analysis

  Authors: Patricia S. Conville, John F. Keiser, Frank G. Witebsky

  Diagnostic Microbiology and Infectious Disease.

  Three methods of concentrating 1 ml aliquots from BACTEC 13A bottles containing patient blood samples were evaluated for testing with the Gen-Probe Rapid Diagnostic System for Mycobacteria aviumThree methods of concentrating 1 ml aliquots from BACTEC 13A bottles containing patient blood samples were evaluated for testing with the Gen-Probe Rapid Diagnostic System for Mycobacteria avium complex: 1. using no reagents, 2. using both lysing and wash reagents; and 3. using lysing reagent only. Aliquots from 13As containing human blood and seeded with eight mycobacterial species were also concentrated directly and using both regents. Results for samples containing M. avium were as follows: 1. using the direct concentration technique 34 of 47 samples (72%) gave unequivocally positive results; 2. 43 of 47 samples (92%) concentrated using both reagents gave positive results; 3. the technique using lysing reagent only was not found useful. There were no false positives with any of the seeded specimens. We were also able to define the minimum Growth Index necessary to ensure unequivocally positive results for each concentration technique. For those samples containing M. avium these values were 42 for the technique using both reagents and 86 for the direct technique. Direct or reagent concentration of 13A aliquots for testing with Gen-Probe DNA probes provides a rapid, sensitive, and specific means for the identification of M. avium complex bacteremia.