Adaptability and persistence of the emerging pathogen Bordetella petrii

The first described, environmentally isolated, Bordetella petrii was shown to undergo massive genomic rearrangements in vitro. More recently, B. petrii was isolated from clinical samples associated with jaw, ear bone, cystic fibrosis and chronic pulmonary disease. However, the in vivo consequences of B. petrii genome plasticity and its pathogenicity remain obscure. B. petrii was identified from four sequential respiratory samples and a post-mortem spleen sample of a woman presenting with bronchiectasis and cavitary lung disease associated with nontuberculous mycobacterial infection. Strains were compared genetically, phenotypically and by antibody recognition from the patient and from inoculated mice. The successive B. petrii strains exhibited differences in growth, antibiotic susceptibility and recognition by the patient’s antibodies. Antibodies from mice inoculated with these strains recapitulated the specificity and strain dependent response that was seen with the patient’s serum. Finally, we characterize one strain that was poorly recognized by the patient’s antibodies, due to a defect in the lipopolysaccharide O-antigen, and identify a mutation associated with this phenotype. We propose that B. petrii is remarkably adaptable in vivo, providing a possible connection between immune response and bacterial evasion and supporting infection persistence.

Multisite reproducibility of the broth microdilution method for susceptibility testing of Nocardia species

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 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 intralaboratory reproducibility of susceptibility testing of this group of isolates. Acceptable agreement (>90% agreement at ±1 dilution of the 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.

Sulfonamide resistance in isolates of Nocardia spp. from a US multicenter survey

Recent reports of increasing in vitro sulfonamide resistance in Nocardia prompted us to investigate the findings. Despite the reports, there is a paucity of clinical reports of sulfonamide failure in treatment of nocardia disease. We reviewed 552 recent susceptibilities of clinical isolates of Nocardia from six major laboratories in the United States, and only 2% of the isolates were found to have resistant MICs of trimethoprim-sulfamethoxazole and/or sulfamethoxazole. We hypothesize that the discrepancies in the apparent sulfonamide resistance between our study and the previous findings may be associated with difficulty in the laboratory interpretation of in vitro MICs for trimethoprim-sulfamethoxazole and sulfamethoxazole and the lack of quality controls for Nocardia for these agents.

Nucleic acid amplification tests for diagnosis of smear-negative TB in a high HIV-prevalence setting: a prospective cohort study

BACKGROUND

Nucleic acid amplification tests are sensitive for identifying Mycobacterium tuberculosis in populations with positive sputum smears for acid-fast bacilli, but less sensitive in sputum-smear-negative populations. Few studies have evaluated the clinical impact of these tests in low-income countries with high burdens of TB and HIV.

METHODS

We prospectively enrolled 211 consecutive adults with cough ≥2 weeks and negative sputum smears at Mulago Hospital in Kampala, Uganda. We tested a single early-morning sputum specimen for Mycobacterium tuberculosis DNA using two nucleic acid amplification tests: a novel in-house polymerase chain reaction targeting the mycobacterial secA1 gene, and the commercial Amplified® Mycobacterium tuberculosis Direct (MTD) test (Gen-Probe Inc, San Diego, CA). We calculated the diagnostic accuracy of these index tests in reference to a primary microbiologic gold standard (positive mycobacterial culture of sputum or bronchoalveolar lavage fluid), and measured their likely clinical impact on additional tuberculosis cases detected among those not prescribed initial TB treatment.

RESULTS

Of 211 patients enrolled, 170 (81%) were HIV-seropositive, with median CD4+ T-cell count 78 cells/µL (interquartile range 29-203). Among HIV-seropositive patients, 94 (55%) reported taking co-trimoxazole prophylaxis and 29 (17%) reported taking antiretroviral therapy. Seventy-five patients (36%) had culture-confirmed TB. Sensitivity of MTD was 39% (95% CI 28-51) and that of secA1 was 24% (95% CI 15-35). Both tests had specificities of 95% (95% CI 90-98). The MTD test correctly identified 18 (24%) TB patients not treated at discharge and led to a 72% relative increase in the smear-negative case detection rate.

CONCLUSIONS

The secA1 and MTD nucleic acid amplification tests had moderate sensitivity and high specificity for TB in a predominantly HIV-seropositive population with negative sputum smears. Although newer, more sensitive nucleic acid assays may enhance detection of Mycobacterium tuberculosis in sputum, even currently available tests can provide substantial clinical impact in smear-negative populations.

Restriction fragment length polymorphism typing demonstrates substantial diversity among Pneumocystis jirovecii isolates

Better understanding of the epidemiology and transmission patterns of human Pneumocystis should lead to improved strategies for preventing Pneumocystis pneumonia (PCP). We have developed a typing method for Pneumocystis jirovecii that is based on restriction fragment length polymorphism (RFLP) analysis after polymerase chain reaction amplification of an approximately 1300 base-pair region of the msg gene family, which comprises an estimated 50-100 genes/genome. The RFLP pattern was reproducible in samples containing >1000 msg copies/reaction and was stable over time, based on analysis of serial samples from the same patient. In our initial analysis of 48 samples, we found that samples obtained from different individuals showed distinct banding patterns; only samples obtained from the same patient showed an identical RFLP pattern. Despite this substantial diversity, samples tended to cluster on the basis of country of origin. In an evaluation of samples obtained from an outbreak of PCP in kidney transplant recipients in Germany, RFLP analysis demonstrated identical patterns in samples that were from 12 patients previously linked to this outbreak, as well as from 2 additional patients. Our results highlight the presence of a remarkable diversity in human Pneumocystis strains. RFLP may be very useful for studying clusters of PCP in immunosuppressed patients, to determine whether there is a common source of infection.

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

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 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

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 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.

Granulibacter bethesdensis gen. nov., sp. nov., a distinctive pathogenic acetic acid bacterium in the family Acetobacteraceae

A Gram-negative, aerobic, coccobacillus to rod-shaped bacterium was isolated from three patients with chronic granulomatous disease. The organism was subjected to a polyphasic taxonomic study. A multilocus phylogenetic analysis based on the 16S rRNA gene, the internal transcribed spacer (ITS) region and the RecA protein demonstrated that the organism belongs to a new sublineage within the acetic acid bacteria in the family Acetobacteraceae. Phenotypic features are summarized as follows: the organism grew at an optimum temperature of 35-37 degrees C and optimum pH of 5.0-6.5. It produced a yellow pigment, oxidized lactate and acetate, the latter weakly, produced little acetic acid from ethanol and could use methanol as a sole carbon source. The two major fatty acids were a straight-chain unsaturated acid (C18:1omega7c) and C16:0. The DNA base composition was 59.1 mol% G+C. The very weak production of acetic acid from ethanol, the ability to use methanol, the yellow pigmentation and high optimum temperature for growth distinguished this organism from other acetic acid bacteria. The unique phylogenetic and phenotypic characteristics suggest that the bacterium should be classified within a separate genus, for which the name Granulibacter bethesdensis gen. nov., sp. nov. is proposed. The type strain is CGDNIH1T (=ATCC BAA-1260T=DSM 17861T).

Analysis of secA1 gene sequences for identification of Nocardia species

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 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.

Clinical and laboratory features of the Nocardia spp. based on current molecular taxonomy

The recent explosion of newly described species of Nocardia results from the impact in the last decade of newer molecular technology, including PCR restriction enzyme analysis and 16S rRNA sequencing. These molecular techniques have revolutionized the identification of the nocardiae by providing rapid and accurate identification of recognized nocardiae and, at the same time, revealing new species and a number of yet-to-be-described species. There are currently more than 30 species of nocardiae of human clinical significance, with the majority of isolates being N. nova complex, N. abscessus, N. transvalensis complex, N. farcinica, N. asteroides type VI (N. cyriacigeorgica), and N. brasiliensis. These species cause a wide variety of diseases and have variable drug susceptibilities. Accurate identification often requires referral to a reference laboratory with molecular capabilities, as many newer species are genetically distinct from established species yet have few or no distinguishing phenotypic characteristics. Correct identification is important in deciding the clinical relevance of a species and in the clinical management and treatment of patients with nocardial disease. This review characterizes the currently known pathogenic species of Nocardia, including clinical disease, drug susceptibility, and methods of identification.

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

Molecular 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"

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. 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

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 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

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 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.

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

A 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.

Nocardia infection in chronic granulomatous disease

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 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.

Lack of usefulness of carbon utilization tests for identification of Mycobacterium mucogenicum

Carbon utilization tests have proven to be useful for the identification of some species of rapidly growing mycobacteria and have been described as one of the few tests useful for the differentiation of Mycobacterium mucogenicum from other rapid growers. We have found the carbon utilization tests to be unreliable for the identification of patient isolates of this species. In this study, using 28 isolates of rapidly growing mycobacteria, we examined several variables which might have an effect on results of citrate, inositol, and mannitol utilization: inoculum concentration, incubation temperature, and medium manufacturer. None of these variables affected results obtained for most species of rapid growers or for ATCC strains of M. mucogenicum. Results for patient isolates of M. mucogenicum were found to be inconsistent regardless of the methodology employed and resulted in an ambiguous identification of these isolates or an incorrect identification as Mycobacterium chelonae. Molecular or cell wall analysis may be the best technique to employ for accurate identification of M. mucogenicum.

Identification of nocardia species by restriction endonuclease analysis of an amplified portion of the 16S rRNA gene

Identification of clinical isolates of Nocardia to the species level is important for defining the spectrum of disease produced by each species and for predicting antimicrobial susceptibility. We evaluated the usefulness of PCR amplification of a portion of the Nocardia 16S rRNA gene and subsequent restriction endonuclease analysis (REA) for species identification. Unique restriction fragment length polymorphism (RFLP) patterns were found for Nocardia sp. type strains (except for the N. asteroides type strain) and representative isolates of the drug pattern types of Nocardia asteroides (except for N. asteroides drug pattern type IV, which gave inconsistent amplification). A variant RFLP pattern for Nocardia nova was also observed. Twenty-eight clinical isolates were evaluated both by traditional biochemical identification and by amplification and REA of portions of the 16S rRNA gene and the 65-kDa heat shock protein (HSP) gene. There was complete agreement among the three methods on identification of 24 of these isolates. One isolate gave a 16S rRNA RFLP pattern consistent with the biochemical identification but was not identifiable by its HSP gene RFLP patterns. Three isolates gave 16S rRNA RFLP patterns which were inconsistent with the identification obtained by both biochemical tests and HSP gene RFLP; sequence analysis suggested that two of these isolates may belong to undefined species. The PCR and REA technique described appears useful both for the identification of clinical isolates of Nocardia and for the detection of new or unusual species.

Variables affecting results of sodium chloride tolerance test for identification of rapidly growing mycobacteria

The sodium chloride tolerance test is often used in the identification of rapidly growing mycobacteria, particularly for distinguishing between Mycobacterium abscessus and Mycobacterium chelonae. This test, however, is frequently unreliable for the identification of some species. In this study we examined the following variables: medium manufacturer, inoculum concentration, and atmosphere and temperature of incubation. Results show that reliability is improved if the test and control slants are inoculated with an organism suspension spectrophotometrically equal to a 1 McFarland standard. Slants should be incubated at 35 degrees C in ambient air and checked weekly for 4 weeks. Growth on control slants should be critically evaluated to determine the adequacy of the inoculum; colonies should number greater than 50. Salt-containing media should be examined carefully to detect pinpoint or tiny colonies, and colonies should number greater than 50 for a positive reaction. Concurrent use of a citrate slant may be helpful for distinguishing between M. abscessus and M. chelonae. Molecular methodologies are probably the most reliable means for the identification of rapidly growing mycobacteria and should be used, if possible, when unequivocal species identification is of particular importance.

Clarithromycin lowers plasma zidovudine levels in persons with human immunodeficiency virus infection

The use of antiretroviral agents and drugs for the treatment and prophylaxis of opportunistic infections has lengthened the survival of persons with AIDS. In the era of multidrug therapy, drug interactions are important considerations in designing effective and tolerable regimens. Clarithromycin has had a significant impact on the treatment of disseminated Mycobacterium avium complex infection, and zidovudine is the best-studied and one of the most widely used antiretroviral agents in this population. We conducted a study to determine the maximally tolerated dose of clarithromycin and the pharmacokinetics of clarithromycin and zidovudine individually and in combination. Mixing studies were conducted to simulate potential interaction in the gastric environment. The simultaneous administration of zidovudine and clarithromycin had little impact on the pharmacokinetics of clarithromycin or of its major metabolite. However, coadministration of zidovudine and clarithromycin at three doses (500 mg orally [p.o.] twice daily [b.i.d.], 1,000 mg p.o. b.i.d., and 2,000 mg p.o. b.i.d.) reduced the maximum concentration of zidovudine by 41% (P < 0.005) and the area under the concentration-time curve from 0 to 4 h for zidovudine by 25% (P < 0.05) and increased the time to maximum concentration of zidovudine by 84% (P < 0.05), compared with zidovudine administered alone. Mixing studies did not detect the formation of insoluble complexes due to chelation, suggesting that the decrease in zidovudine concentrations results from some other mechanism. Simultaneous administration of zidovudine and clarithromycin appears to decrease the levels of zidovudine in serum, and it may be advisable that these drugs not be given at the same time. Drug interactions should be carefully evaluated in persons with advanced human immunodeficiency virus infection who are receiving multiple pharmacologic agents.

Effect of PANTA on growth of Mycobacterium kansasii in BACTEC 12B medium

Mycobacterium kansasii isolates from two patients showed relatively slow growth in BACTEC 12B medium (12B) (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) compared with the more rapid growth of these isolates on solid media. This finding prompted an evaluation of the effect of PANTA (Becton Dickinson) on the growth rate of these isolates. Suspensions of one isolate from each of these two patients (A and B), six additional isolates from six other patients (C through H), and one M. kansasii American Type Culture Collection isolate were inoculated into 12B with PANTA, 12B with reconstituting fluid only, and Middlebrook 7H11 agar plates (Remel, Lenexa, Kans.). For the isolates from patients A and B, the average times to detection for 12B with PANTA, 12B with reconstituting fluid, and Middlebrook 7H11 agar were 12.3, 7.4, and 9.0 days, respectively. For the remaining six patient isolates and the American Type Culture Collection strain, the average times to detection for these media were 9.2, 8.1, and 9.6 days. Susceptibility tests performed with the isolates from patients A and B with the individual component antibiotics of PANTA and testing of four of the other isolates with nalidixic acid alone suggested that nalidixic acid exerts some degree of inhibition on the growth of M. kansasii. The eight patient isolates were also inoculated onto Lowenstein Jensen medium (Remel) and onto a variety of selective mycobacterial media containing nalidixic acid and other antimicrobial agents. All isolates showed some degree of inhibition on at least one of these selective media.

Antimicrobial susceptibilities of mycobacteria as determined by differential light scattering and correlation with results from multiple reference laboratories

The DAWN Model B laser light scattering instrument (Wyatt Technology Corporation, Santa Barbara, Calif.) was evaluated to assess its potential to provide rapid mycobacterial antimicrobial susceptibility test results. For Mycobacterium tuberculosis there was a clear separation between susceptible and resistant results with the isolates tested, and there was excellent correlation with reference laboratory results. For Mycobacterium avium there was no obvious breakpoint between susceptible and resistant results with the isolates tested, and correlation with reference laboratory results was less good than for M. tuberculosis. However, for M. avium there was also less agreement among reference laboratory results than for M. tuberculosis. Significant instrument design and software program changes would be required for the instrument to become a useful tool for mycobacterial susceptibility testing in the diagnostic laboratory.

Orally administered clarithromycin for the treatment of systemic Mycobacterium avium complex infection in children with acquired immunodeficiency syndrome

OBJECTIVE

To determine the safety, tolerance, pharmacokinetics, and antimycobacterial activity of orally administered clarithromycin in children with acquired immunodeficiency syndrome and disseminated Mycobacterium avium complex (MAC) infection.

DESIGN

Phase I study with a 10-day pharmacokinetic phase followed by a 12-week continuation therapy phase.

PATIENTS

Twenty-five patients with a median age of 8.3 years were enrolled. Ten were receiving zidovudine and 13 were receiving didanosine at the time of enrollment.

INTERVENTION

Clarithromycin suspension was administered to each patient at one of three dose levels: 3.75, 7.5, and 15 mg/kg per dose every 12 hours. Clarithromycin and antiretroviral pharmacokinetics were measured during single-drug and concurrent-drug administration. Clinical and laboratory monitoring was performed biweekly.

MEASUREMENTS AND MAIN RESULTS

Clarithromycin was well tolerated at all dose levels. Plasma clarithromycin concentrations increased proportionately with increasing doses, and significant pharmacokinetic interactions were not observed during concurrent administration with zidovudine or didanosine. Decreases in mycobacterial load in blood were observed only at the highest clarithromycin dose level. Decreased susceptibility to clarithromycin developed rapidly (within 12 to 16 weeks) in the majority of MAC strains isolated from study patients.

The laboratory diagnosis of mycobacterial diseases

Recent developments in diagnostic mycobacteriology are surveyed with emphasis on laboratory capabilities relevant to the more rapid and accurate detection and identification of mycobacterial pathogens. Some terminologic problems are reviewed, and some newly recognized mycobacterial pathogens are discussed. Newer methodologies presented in some detail include the radiometric technique for detection, identification, and susceptibility testing of mycobacteria, and the use of DNA probes for identification of mycobacterial species and species complexes. The utility of other developing methodologies, such as polymerase chain reaction technology, analysis of body fluids for tuberculostearic acid, and the use of ELISA are also assessed.

Inter-bottle transfer of mycobacteria by the BACTEC 460

As a result of several episodes of inter-bottle transfer of molds and mycobacteria in our BACTEC 460 TB System (Johnston Laboratories, Towson, MD), we designed some experiments to attempt to reproduce the transfer process. We demonstrated that organism transfer could occur with our instrument during routine use without any indication of instrument malfunction. Utilizing a redesigned A1B4 circuit board that extends the time of the needle heating cycle to 85 sec and increases the needle heater maximum temperature, we were not able to effect organism transfer even from bottles with very high growth indices. We also demonstrated that even with the redesigned A1B4 circuit board, the needles were not heated sufficiently to sterilize them after direct insertion into a mycobacterial suspension. Organism transfer also occurred while using a second redesigned A1B4 circuit board which extends the needle heating cycle to 75 sec. Users should be aware that organism transfer can occur with the BACTEC 460 under certain circumstances. Maintenance and testing recommendations from Johnston Laboratories should be scrupulously followed, and we suggest some additional procedures that might further reduce the possibility of organism transfer.

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

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 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 reagents. 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 un-equivocally 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.

Mycobacteremia caused by simultaneous infection with Mycobacterium avium and Mycobacterium intracellulare detected by analysis of a BACTEC 13A bottle with the Gen-Probe kit

Simultaneous infection with Mycobacterium avium and Mycobacterium intracellulare in an AIDS patient was suspected after direct analysis of two BACTEC 13A blood cultures with the Gen-Probe kit for M. avium complex. A mixed infection was confirmed by evaluating isolated colonies. The Gen-Probe kit may provide a simple technique for detecting mixed M. avium-M. intracellulare infections.

Comparison of BACTEC 13A medium and Du Pont isolator for detection of mycobacteremia

BACTEC 13A medium (Johnston Laboratories, Towson, Md.) was compared with Isolator (Du Pont Co., Wilmington, Del.) concentrate for sensitivity, speed, and technical ease of isolation of mycobacteria from paired patient blood samples. Of 72 positive cultures, 63 were positive by both systems. Five positive cultures were detected by BACTEC 13A medium alone, and four were detected by Isolator alone. The median numbers of days to positivity were 12 for BACTEC 13A medium and 14 for Isolator concentrate. BACTEC 13A medium has an advantage over the Isolator in requiring less laboratory manipulation of the specimen but has the disadvantages of not providing isolated colonies or quantitation of organisms. Some technical problems with contamination in both systems are also discussed.

Rapid identification of enterococci by pyrrolidonyl aminopeptidase activity (PYRase)

Group A streptococci and enterococci can be differentiated from other streptococci by their ability to cleave pyrrolidonyl beta-naphthylamide (PYRase). We evaluated two PYRase systems [Strep-A-Chek (SAC), E-Y Laboratories, San Mateo, CA; Strep-A-Fluor (SAF), BioSpec, Inc., Dublin, CA) for the presumptive identification of enterococci. Initially, 40 enterococcal and 21 nonenterococcal streptococci were tested, retrospectively. A prospective comparison of SAC and SAF to bile-esculin reaction (BE) was then incorporated into our routine procedure for the identification of non-beta-hemolytic streptococcal colonies from cultures. All isolates were speciated using standard biochemical tests. We encountered 85 enterococcal and 26 nonenterococcal isolates. Tests were performed on colonies from primary plates whenever possible (77 isolates). Sensitivity and specificity of both SAC and SAF were greater than 96% in identifying enterococci from routine cultures. These PYRase tests were cost-effective, easily adaptable to work-flow, and yielded results within 30 min. Thus, PYRase testing appears to be a reasonable alternative for the identification of enterococci in the clinical laboratory.

Rapid identification of group A streptococci by the Strep-A-Fluor system

Group A streptococci can be rapidly identified by the Strep-A-Fluor system (Bio-Spec Inc., Dublin, CA), which uses a specific aminopeptidase to hydrolize L-pyrrolidonyl-beta-naphthylamide. In pure subcultured colonies and in isolated colonies from primary culture plates, the Strep-A-Fluor system had 100% sensitivity and 100% specificity compared with the results of Streptex latex agglutination (Wellcome Research Laboratories, Research Triangle Park, NC). However, in mixed culture from primary culture plates, the sensitivity and specificity were 73% and 95%, respectively. Furthermore, in a routine laboratory setting, the sensitivity was only 91% both from pure subcultured colonies and from isolated colonies from primary culture plates. Contamination with organism other than group A streptococci that are capable of hydrolyzing L-pyrrolidonyl-beta-naphthylamide may explain the low specificity in mixed culture. Deterioration of the buffer reagent due to prolonged use may account for the low sensitivity in a routine laboratory setting.