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Journal of Clinical Microbiology, June 2004, p. 2495-2500, Vol. 42, No. 6
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.6.2495-2500.2004
June M. Brown,1* Michelle E. Carvalho,1 Dannie G. Hollis,1 Roger E. Morey,1 and L. Barth Reller2
Meningitis and Special Pathogens Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333,1 Clinical Microbiology Laboratory and Departments of Pathology and Medicine, Duke University School of Medicine, Durham, North Carolina 277102
Received 23 January 2004/ Returned for modification 8 March 2004/ Accepted 16 March 2004
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Since these initial reports, to our knowledge, there have been only three additional reports of O. turbata infection (7, 11, 17). Two catheter-related bacteremias, one in a patient with acute myelogenous leukemia (11) and the other in a patient with AIDS and a coinfection with Comamonas acidovorans (7), have been described. The remaining report described an axillary abscess in a patient with AIDS (17). All these reports involved immunocompromised patients with chronic underlying conditions (7, 11, 17, 18); three of the infections were associated with implanted foreign bodies (homograft valves, catheters), whose removal was necessary for effective cure of the patients (7, 11, 18). There was a high frequency of relapse (75% in spite of treatment) among these patients. However, because of the paucity of infected patients, no reliable conclusions regarding the efficacy of specific antimicrobial therapy for O. turbata infections could be determined.
To test the hypothesis generated by the original investigation team that these patients' infections were linked to use of contaminated homograft valves in the medical center (18), we compared genetic and phenetic characteristics of 12 epidemiologically related isolates (four blood isolates from patient 1, one blood isolate from patient 2, and seven homograft isolates all from the same medical center) with the type strain of O. turbata, four unrelated clinical reference isolates of O. turbata, one reference isolate of CDC group A-3, and the type strain and a reference isolate of Cellulomonas hominis (6).
(This work was presented in part at the 96th General Meeting of the American Society for Microbiology, New Orleans, La., 19 to 23 May 1996.)
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TABLE 1. Isolates used in this studya
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Antimicrobial susceptibility studies were performed by a previously described broth microdilution method with cation-supplemented Mueller-Hinton broth (12). The antimicrobial agents tested were amikacin, amoxicillin-clavulanic acid, ampicillin, cefotaxime, ceftriaxone, ciprofloxacin, doxycycline, erythromycin, imipenem, minocycline, sulfamethoxazole (SMX), trimethoprim-sulfamethoxazole (TMP-SMX), and vancomycin. Plates were incubated for 48 h at 35°C. The methods of testing and the breakpoints for resistance for this group of rare organisms have not been standardized or approved by the National Committee for Clinical Laboratory Standards (NCCLS). Therefore, the breakpoints for resistance used were those of the NCCLS for bacteria that grow aerobically (13). A direct beta-lactamase assay, the chromogenic cephalosporin nitrocefin method, was used on representative isolates (14).
Chemotaxonomic analyses. The methods used for whole-cell analyses for diaminopimelic acid and monosaccharides are those described by Berd (2).
DNA purification and ribotyping. Strains were subcultured from HIA into Trypticase soy broth (Becton Dickinson, Sparks, Md.) and grown for 1 to 2 days at 35°C before being harvested by centrifugation at 3,795 x g. DNA was purified from lysed protoplasts as described previously by Lasker et al. (9). Genomic DNA (1 to 2 mg/ml) was digested with 20 U of SmaI and BglI (Roche Molecular Biochemicals, Indianapolis, Ind.) for 8 h at 35°C in the buffer recommended by the manufacturer. DNA fragments were then transferred to a nylon membrane (Nytran; Schleicher & Schuell, Keene, N.H.) and hybridized with digoxigenin-labeled cDNA derived from 16S and 23S rRNA of Escherichia coli by reverse transcription as described previously (15). Ribosomal DNA-containing fragments were visualized according to the Genius kit (Roche Molecular Biochemicals) protocol.
16S rDNA sequencing. Purified genomic DNA was amplified using an Expand high fidelity PCR system (Roche Diagnostics Corporation, Indianapolis, Ind.) proofreading enzyme Pfu (1) to increase fidelity of products. The protocol was modified with the addition of dimethyl sulfoxide (4) to increase the yield of high G+C templates. Briefly, each 50-µl portion contained approximately 10 ng of DNA, 2.5 U of polymerase, 1.5 mM MgCl2, 5% (vol/vol) dimethyl sulfoxide, 200 µM dNTPs, and 100 nM each primers fL1 and rL1 (21). Amplification was performed on an ABI 9700 (Applied Biosystems, Foster City, Calif.) thermocycler at 94°C for 5 min, 35 cycles of 94°C for 15 s, 50°C for 15 s, 72°C for 90 s, and finalized by a single extension of 72°C for 5 min followed by a 4°C hold.
Amplified products were confirmed by running 5 µl on a 1.2% agarose gel with a 500-bp ladder for 30 min at 85 V. Excess dNTPs and primers were inactivated with the ExoSAP method (United States Biochemical Corporation, Cleveland, Ohio). Cycle sequencing was performed with Big Dye v.2 dye terminator chemistry (Applied Biosystems) by using standard protocols with small subunit primers (5, 8, 20, 25). Excess dyes were removed with magnetic carboxylate beads (Agencourt Bioscience, Beverly, Mass.), and reactions were sequenced on an ABI 3100 analyzer (Applied Biosystems). Sequences were assembled in GCG's Seqmerge and trimmed to a minimum of two confirming reads. Unique sequences were aligned and compared with those of other bacterial 16S rRNA gene sequences available in GenBank. Related entries were aligned in Pileup and trimmed to consensus, and further analysis was performed in Bioedit and Treecon. In Bioedit, the sequences were realigned in Clustal W with 1,000 bootstraps, and a distance matrix was created. In Treecon, distances of aligned sequences were estimated with Jukes-Cantor and bootstrapped 1,000 times, and tree topology was determined by neighbor joining (3).
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Patient 2's blood isolate and one homograft valve isolate that was originally identified as O. turbata were identical to the clinical reference strain of CDC group A-3, W6117, and these isolates differed from all O. turbata isolates in their production of acid from L-rhamnose, their inability to produce substrate hyphae, and the lack of gelatinase. They differed from C. hominis in their resistance to cefotaxime, ciprofloxacin, and erythromycin. Characteristics that distinguished these isolates from the type strains of O. turbata and C. hominis and the reference clinical isolates are given in Table 2.
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TABLE 2. Comparison of patient 1's, patient 2's, and the homograft valve isolates with the type and clinical reference strains of O. turbata; C. hominis, and CDC group A-3
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None of the isolates contained either the meso or the L isomer of diaminopimelic acid in the whole-cell analysis; however, all isolates contained galactose as the characteristic whole-cell carbohydrate.
Representative ribotype patterns with BglI-digested DNA are given in Fig. 1. All of patient 1's isolates (n = 4) and six homograft valves isolates (lanes 7 to 10, only 4 of 10 isolates shown) were identical but differed from the patterns of the type strain (lane 2), the unrelated clinical reference isolates (lanes 3 to 6) of O. turbata, patient 2's isolate and one homograft valve isolate (lanes 11 and 12), the type strain of C. hominis (lane 13), and the unrelated clinical reference isolate of CDC group A-3 (lane 14). Patient 2's isolate and one homograft valve isolate (lanes 11 and 12) were identical and were different from the ribotype patterns of the type and clinical reference strains of O. turbata (lanes 2 to 6), patient 1's isolates (lanes 7 to 10), the type strain of C. hominis (lane 13), and the unrelated clinical isolate of CDC group A-3 (lane 14) (Fig. 1). When genomic DNA from patient 1's isolates and six homograft valve isolates was digested with SmaI, the patterns were identical to each other and to the clinical reference isolates of O. turbata (W2796 and W6123) but differed from those of the type strain, O. turbata ATCC 25835, and clinical reference strains W4083 and W6035. When genomic DNA from patient 2's isolate and one homograft valve isolate was digested with SmaI, the patterns were identical to each other and the clinical reference isolate W6117 of CDC group A-3, but these ribotype patterns differed from those of the type strain DSM 9581 of C. hominis and the type strain ATCC 25835 of O. turbata (data not shown).
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FIG. 1. Ribotype patterns from BglI-digested genomic DNAs of medical center isolates and type and clinical reference isolates of O. turbata, CDC group A-3, and C. hominis. Lane 1, bacteriophage 8 DNA molecular size marker digested with EcoRI and HindIII; lane 2, type strain O. turbata ATCC 25835; lanes 3 to 6, clinical reference isolates of O. turbata, W6123, W2796, W4083, and W6035, respectively; lanes 7 to 10, 4 of 10 medical center isolates of O. turbata, W2622, W2728, W2729, and W6122 (patient 1's blood isolates) (homograft valve isolates [n = 6] not shown); lanes 11 and 12, medical center isolates of CDC group A-3, W6124 (homograft valve) and W6929 (patient 2's blood isolate), respectively; lane 13, type strain C. hominis DSM 9581; lane 14, clinical reference isolate of CDC group A-3, W6117.
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FIG. 2. Phylogenetic tree constructed by the neighbor-joining method showing the position of W6122 (patient 1's blood isolate) within the Cellulosimicrobium-Cellulomonas-Oerskovia lineage of the gram-positive bacilli with high G+C contents.
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FIG. 3. Phylogenetic tree constructed by the neighbor-joining method showing the position of W6929 (patient 2's blood isolate) within the Cellulomonas-Oerskovia-Sanguibacter lineage of the gram-positive bacilli with high G+C contents.
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Patient 1's blood isolates and six homograft valve isolates differed from the type strain and the clinical reference isolates of O. turbata by resistance to antimicrobial agents: one clinical isolate was susceptible to amikacin, two clinical isolates were susceptible and two were intermediately susceptible to cefotaxime, the type strain and three clinical isolates were susceptible to erythromycin, and the type strain and two clinical isolates were susceptible to TMP-SMX (Table 2). These differences in antimicrobial susceptibility patterns emphasize the need for determining MIC patterns for clinically significant O. turbata isolates. The initial study occurred almost a quarter of a century ago; at the time, information on optimal treatment of O. turbata endocarditis was lacking. Currently, based on the in vitro results in this study and previous experience with related species, vancomycin would probably be considered the drug of choice (19). This antimicrobial agent is bactericidal and has good in vitro activity to all of the oerskoviae; however, the in vivo activity of vancomycin as effective therapy for endocarditis caused by O. turbata or CDC group A-3 remains unproven.
The development of molecular typing methods has given the clinical laboratory powerful tools to allow a detailed study of the epidemiology of bacterial infections. Our ribotyping data indicate that the problem of probable iatrogenic endocarditis in the medical center was more complicated than originally suspected. Two unique clusters of bacterial isolates were responsible: one cluster of 10 isolates of O. turbata and the other cluster of two isolates of CDC group A-3 were identified based on ribotype patterns, demonstrating the usefulness of ribotyping in furthering the understanding of this epidemiologic investigation. The identical ribotype bands between the CDC group A-3 endocarditis blood isolate and the reevaluated homograft valve isolate, previously identified as O. turbata, were unexpected.
The importance of characterizing these archival O. turbata and CDC group A-3 isolates is evident. This molecular epidemiologic study supports the hypothesis that the homograft valve-related endocarditis was associated with the practices of obtaining and preserving the cadaveric homograft valves at this medical center. In addition, for strains that are difficult to analyze phenotypically, ribotyping has been shown to be useful in species identification, as has been demonstrated for other nocardioform bacteria.
When we analyzed the relatedness of the ribotype patterns for patient 1 and six homograft valve isolates digested with SmaI (the species-specific enzyme for this group of related organisms), we found they had bands that were identical to those of two clinical reference isolates of O. turbata but had only one of four bands in common with the type strain of O. turbata and clinical reference strain W6035 and one of three in common with clinical reference strain W4083. The molecular phylogenetic study revealed that patient 1's blood isolate is most closely related to the genus Cellulosimicrobium.
When we analyzed the ribotype patterns from the SmaI-digested DNAs of patient 2's isolate and one homograft valve isolate, we found they had one of three bands in common with the type strain of O. turbata, bands identical to those of the clinical reference isolate W6117 of CDC group A-3, and one of three bands in common with the type strain of C. hominis. This suggests that one homograft and patient 2 were infected with a new species within the heterogenous CDC group A-3 that was identical to W6117. The phylogenetically distinct position of patient 2's blood isolate (W6929) in the 16S rRNA gene phylogram suggests that this group represents a new species only distantly related to the genus Oerskovia but related to the genus Cellulomonas (Fig. 3).
Further studies of DNA-DNA hybridization will show whether 16S rRNA gene sequencing may assist in the taxonomic classification of these two groups.
With the extended survival of severely compromised patients and the increased use of long-term indwelling catheters and cadaveric homografts, it is highly probable that these microorganisms will be encountered more frequently. Knowledge of the reservoir of these species, their survival capabilities within the environment, their resistance to antimicrobial agents, and newer molecular techniques for strain comparison may assist in more efficient identification and control of O. turbata- and CDC group A-3-associated infections in the future.
Present address: Division of Epidemiology and Surveillance, National Immunization Program, Centers for Disease Control and Prevention, Atlanta, GA 30333. ![]()
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