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Journal of Clinical Microbiology, August 2005, p. 3713-3717, Vol. 43, No. 8
0095-1137/05/$08.00+0 doi:10.1128/JCM.43.8.3713-3717.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Department of Laboratory Medicine, Social Insurance Central General Hospital, Tokyo, Japan,1 Gifu University Graduate School of Medicine, Gifu, Japan2
Received 2 December 2004/ Returned for modification 4 February 2005/ Accepted 17 February 2005
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During the management of two patients, one with acute myelocytic leukemia and one with myelodysplastic syndrome, we recovered two multidrug-resistant, lipophilic, asaccharolytic, urease-negative isolates from blood cultures. In addition, three other clinically significant, lipophilic, multidrug-resistant corynebacteria were recovered, bringing the total to five isolates resistant to antimicrobial agents at a level not previously observed. Because the isolates could not be assigned to any of the established taxa of coryneform bacteria, we studied these five strains further using a polyphasic taxonomic approach that included both phenotypic and molecular genetic methods. On the basis of the results of this investigation, we propose that our isolates represent a new Corynebacterium species, Corynebacterium resistens sp. nov.
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Antimicrobial agent susceptibility test. MICs for penicillin G, cefazolin, cefotiam, cefmetazole, cefepime, imipenem, amikacin, clindamycin, ciprofloxacin, minocycline, teicoplanin, and vancomycin were determined with a CLSI (formerly NCCLS) microtiter broth dilution method citation supplemented with 3% lysed horse blood (Eiken Chemical Co., Ltd., Tokyo, Japan) (12). On the basis of a consultation with an infectious disease, we set the clinically relevant drug concentration range at 0.13 to 64 µg/ml, with the exception of clindamycin and glycopeptides, which were set at 0.06 to 16 µg/ml and 0.5 to 16 µg/ml, respectively. Because no CLSI interpretive standard for corynebacteria exists, MICs were analyzed for comparative purposes. Microdilution trays were incubated aerobically at 35°C for 48 h.
Chemotaxonomic investigations. Cellular fatty-acid compositions were measured by means of the Sherlock Microbial Identification System (MIDI, Inc., Newark, DE) and the method described by Kosako et al. (9).
16S rRNA gene sequence and analysis. The 16S rRNA genes of the isolates in this study were amplified by PCR as described previously (5). The nucleotide sequence was determined with an automatic sequencer (model 3100, Applied Biosystems, Calif., USA) and a dye-terminator reaction kit (Applied Biosystems). The sequences of other Corynebacterium species used for alignment and for calculating homology levels were obtained from the DNA Data Bank of Japan (DDBJ), GenBank, and the European Molecular Biology Laboratory (EMBL) databases. CLUSTAL W software, originally described by Thompson et al. (17), was used to align the sequences, and the phylogenetic distance was calculated with the neighbor-joining method. The phylogenetic tree was drawn with TREEVIEW software (14).
DNA-DNA hybridization. DNA from each strain was prepared by the standard procedure of Marmur (10). Quantitative microplate DNA-DNA hybridization was carried out as described previously (3). Hybridization experiments were carried out at 37°C (optimal conditions) and 47°C (stringent conditions) with 2x SSC (1x SSC is 0.15 M NaCl plus 0.015 M sodium citrate) and 50% formamide. The optimal temperature was 30°C lower than the denaturation temperature because the formamide lowered the hybridization temperature (11). The type strains used for DNA-DNA hybridization were Corynebacterium auriscanis GTC 1995T (= DSM 44609) and Corynebacterium jeikeium GTC 681T (= IFO 15298). Because C. auriscanis showed the highest 16S rRNA gene sequence homology (98.5%), and C. jeikeium, which also phylogenetically related species, was the multidrug resistant along with our isolates, we selected these two species to clarify whole genome DNA-DNA relationships with our isolates.
Biochemical profiles. The strains were characterized biochemically with the API Coryne, API ZYM, and API 50CH systems (all from bioMérieux, Tokyo, Japan). API Coryne reactions were read after 24 h of incubation at 37°C, and API ZYM reactions were read after 4 h of incubation at 37°C, whereas acid production from carbohydrates was observed after 48 h. API 50CH reactions performed with 50 CHE medium were read after seven days of incubation at 37°C in ambient air.
G+C content. The G+C content of DNA from the isolates was determined by high-pressure liquid chromatography (HPLC) as described previously (4). Briefly, 10 µl of purified DNA (1 mg/ml) was heat denatured, after the DNA solution was cooled, and 10 µl nuclease P1 solution (2 U/ml) was added and incubated at 50°C for 1 h. Then 10 µl alkaline phosphatase solution (2 · 4 U/ml) was added, and the mixture was incubated at 37°C for 30 min. The digested DNA solution was analyzed by HPLC with a packed column (Wakosil 5C18, Wako Co., Ltd., Osaka, Japan). The mol% G+C content was calculated by using that of the Escherichia coli K-12 strain DNA as a standard (51.12 mol% G+C).
Nucleotide sequence accession number. The nucleotide sequence of the 16S rRNA of strain GTC 2026 has been deposited in DDBJ under accession number AB128981.
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Colony morphology. The five strains of coryneform bacteria grew as grayish-white, glistening, pearly colonies of up to 1.0 mm in diameter after 48 h of incubation on TSA with 5% sheep blood. All strains were lipophilic. When Tween 80 was added to a concentration of 1%, colony growth was enhanced, resulting in a colony diameter of 2 to 3 mm.
Susceptibility to antimicrobial agents. The MICs of various antimicrobial agents are given in Table 1. With respect to penicillin, cephalosporins, amikacin, clindamycin, and ciprofloxacin, all five isolates showed MICs beyond the clinically relevant drug concentration range utilized in this study. Four isolates exhibited MICs beyond the clinically relevant drug concentration range established for imipenem and minocycline. Only isolate GTC 2025, which was initially recovered from an outpatient, showed low MICs for imipenem and minocycline. All five isolates exhibited low MICs for the glycopeptides tested in the study.
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TABLE 1. MICs of 12 antimicrobial agents against the five strainsa
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c (37.34%), C16:0 (22.17%), and C18:0 (16.84%), which was consistent with values for other members of the genus Corynebacterium. 16S rRNA analysis. To determine the phylogenetic relatedness of the unknown coryneform isolates, the almost complete 16S rRNA gene sequence (1,418 bases) of a representative strain (GTC 2026) was determined. As shown in Fig. 1, sequence searches of the DDBJ, GenBank, and EMBL databases revealed that the 16S rRNA sequence was highly related to sequences of species within the genus Corynebacterium, with C. auriscanis, C. falsenii, C. jeikeium, and C. urealyticum displaying the highest levels of sequence relatedness (98.5, 96.7, 96.2, and 95.9% sequence similarity, respectively, with the unknown isolate). The unidentified bacterium formed a distinct subline that was close to, albeit distinct from, C. auriscanis, C. falsenii, C. jeikeium, and C. urealyticum. We also determined the partial sequence of the 16S rRNA gene (about 800 bp from the 5' end) from another four strains (GTC 2023, GTC 2024, GTC 2025, and GTC 2027). The four strains and GTC 2026 shared almost identical sequences within this 800bp region only one or two different bases were observed).
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FIG. 1. Dendrogram showing phylogenetic relations of the 16S rRNA gene sequences of Corynebacterium resistens sp. nov. Distances were calculated by the neighbor-joining method. The numbers at the branch points are bootstrap values.
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TABLE 2. DNA-DNA hybridization similarity values
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With API ZYM, alkaline phosphatase, esterase (C4), esterase lipase (C8), leucine arylamidase, acid phosphatase, and naphthol-AS-BI-phosphohydrolase were clearly positive, whereas lipase (C14), cystine, and arylamidase were weakly positive. Reactions for valine arylamidase, trypsin, chymotrypsin,
-galactosidase, ß-galactosidase, ß-glucuronidase,
-glucosidase, ß-glucosidase, N-acetyl-ß-glucosaminidase,
-mannosidase, and
-fucosidase were negative.
With API 50CH, no oxidation was noted even after 7 days reaction. With the overlay of sterile mineral oil, D-tagatose and 5-ketogluconate were positive within 24 h whereas ribose and D-glucose were weakly positive at 24 h and clearly positive when reactions were extended to 72 h. With respect to trehalose, only GTC 2025 was negative among the five strains tested. For L-sorbose, only GTC 2026 was negative. All strains were negative for glycerol, erythritol, D-arabinose, L-arabinose, D-xylose, L-xylose, adonitol, ß-methylxyloside, galactose, D-fructose, D-mannose, rhamnose, dulcitol, inositol, mannitol, sorbitol,
-methyl-D-mannoside,
-methyl-D-glucoside, N-acetylglucosamine, amygdaline, arbutin, esculin, salicin, cellobiose, maltose, lactose, melibiose, sucrose, inulin, melezitose, D-raffinose, starch, glycogen, xylitol, ß-gentiobiose, D-turanose, D-lyxose, D-fucose, L-fucose, D-arabitol, L-arabitol, gluconate, and 2-ketogluconate.
G+C content. The G+C content for strain GTC 2026 was 54.643 mol% (standard deviation, 0.03%).
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TABLE 3. Biochemical characteristics of lipophilic Corynebacterium spp.a
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In the present study, GTC 2027 was isolated on three occasions over 2 days during an episode of sepsis from a 68-year-old male with myelodysplastic syndrome. On the basis of the clinical findings and the recovery of corynebacteria from blood cultures, we considered C. jeikeium the most likely etiologic agent, and minocycline (200 mg/day) was administered. Because the MIC of 8 µg/ml was considered high, we believe that lack of effective therapy contributed to the subsequent death of the patient from sepsis.
Our isolates present a clinical challenge because glycopeptides appear to be the only antimicrobial agents with low MICs. Of the five strains in the present study, only GTC 2025, which was recovered from a patient in an outpatient setting, showed low MICs for imipenem and minocycline. It is thought that exposure to antimicrobial agents in an inpatient setting contributes to increased resistance. Furthermore, as with C. jeikeium, the potential for nosocomial spread increases the clinical significance of our isolates (8, 15). On the basis of our phenotypic and molecular genetic findings, we propose that the unknown multidrug-resistant corynebacteria described above be classified as a new species within the genus Corynebacterium and that the name Corynebacterium resistens sp. nov. be used.
Description of Corynebacterium resistens sp. nov. Corynebacterium resistens (L. adj. resistens, resistant). The descriptive characteristics given below are based on the results of the studies of the five strains. Cells are gram positive, non-spore-forming, and nonmotile. They are typically club-shaped rods, coryneform bacteria (indicative of true Corynebacterium spp.) 1 to 3 µm in length, and arranged as single cells, in pairs, or in small clusters. Growth on TSA with 5% sheep blood demonstrated nonpigmented, grayish-white, glistening, pearly colonies up to 1.0 mm in diameter. Colonies were catalase positive, oxidase negative, nonhemolytic, and very slow growing under anaerobic conditions. Tween 80 enhanced growth, resulting in colonies 2 to 4 mm in diameter; CAMP negative, lipophilic, and nitrate was not reduced. There was no oxidizing resolution of any carbohydrates. However, the fermenting resolution was as follows: D-tagatose, 5-ketogluconate, ribose, and D-glucose were positive. For four of the five strains, trehalose and L-sorbose were positive.
All strains were negative for glycerol, erythritol, D-arabinose, L-arabinose, D-xylose, L-xylose, adonitol, ß-methylxyloside, galactose, D-fructose, D-mannose, rhamnose, dulcitol, inositol, mannitol, sorbitol,
-methyl-D-mannoside,
-methyl-D-glucoside, N-acetylglucosamine, amygdaline, arbutin, esculin, salicin, cellobiose, maltose, lactose, melibiose, sucrose, inulin, melezitose, D-raffinose, starch, glycogen, xylitol, ß-gentiobiose, D-turanose, D-lyxose, D-fucose, L-fucose, D-arabitol, L-arabitol, gluconate, and 2-ketogluconate. Alkaline phosphatase, esterase (C4), esterase lipase (C8), leucine arylamidase, acid phosphatase, and naphthol-AS-BI-phosphohydrolase were clearly positive, whereas lipase (C14), cysteine, and arylamidase were weakly positive. Reactions for valine arylamidase, trypsin, chymotrypsin,
-galactosidase, ß-galactosidase, ß-glucuronidase,
-glucosidase, ß-glucosidase, N-acetyl-ß-glucosaminidase,
-mannosidase, and
-fucosidase were negative. Fatty acids were C18:1
c (37.34%), C16:0 (22.17%), and C18:0 (16.84%). The G+C content of the DNA was 54.643 mol% (standard deviation = 0.03%) by HPLC. The type strain is GTC 2026T (SICGH 158T, JCM 12819T, CCUG 50093T)
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