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Journal of Clinical Microbiology, July 2003, p. 3415-3418, Vol. 41, No. 7
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.7.3415-3418.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Use of Amplified Ribosomal DNA Restriction Analysis for Identification of Ralstonia and Pandoraea Species: Interest in Determination of the Respiratory Bacterial Flora in Patients with Cystic Fibrosis
Christine Segonds,* Sandrine Paute, and Gérard Chabanon
Observatoire Cepacia/Vaincre la Mucoviscidose, Laboratoire de Bactériologie-Hygiène, Hôpital Rangueil-TSA 50032, 31059 Toulouse Cedex 9, France
Received 7 November 2002/
Returned for modification 21 January 2003/
Accepted 24 April 2003

ABSTRACT
The recovery of
Ralstonia and
Pandoraea species from respiratory
tract cultures of patients with cystic fibrosis has recently
been reported. These species are difficult to identify, and
especially to differentiate from
Burkholderia cepacia complex
organisms, with classical methods. The discriminatory power
of amplified ribosomal DNA restriction analysis (ARDRA) within
the two genera was assessed by comparing the restriction profiles
of reference strains of each species by using a panel of six
enzymes already proven suitable for the identification of
Burkholderia species. ARDRA provided differentiation of all the
Ralstonia species tested and of
Pandoraea norimbergensis.
Pandoraea species
P. pnomenusa,
P. sputorum,
P. pulmonicola, and
P. apista were
not discriminated to the species level. This method allowed
the identification of five clinical isolates recovered from
French cystic fibrosis patients as
Ralstonia mannitolilytica.

TEXT
The recovery of various gram-negative bacilli, mainly
Ralstonia and
Pandoraea species, from the sputa of patients with cystic
fibrosis (CF) on
Burkholderia cepacia-selective media has been
recently pointed out (
4,
5). The genus
Ralstonia, described
in 1995 by Yabuuchi et al.(
16), contains environmental gram-negative
bacilli including major plant pathogen
R. solanacearum (
12);
potential bioremediation agents
R. eutropha and the metal-resistant
R. campinensis,
R. metallidurans, and
R. basilensis (
11); and
opportunistic human pathogens. Among strains of clinical importance,
four
Ralstonia species have been isolated from CF patients:
R. pickettii (formerly
Pseudomonas pickettii and
Burkholderia pickettii) (
2),
R. mannitolilytica (formerly
R. pickettii biovar
3/
thomasii) (
5,
10), and quite rarely
R. gilardii (
8) and
R. taiwanensis (
3,
8), whereas
R. paucula (formerly CDC group IV
c-2) has not been involved in CF to date. The novel genus
Pandoraea (
4) contains five species:
P. pnomenusa,
P. sputorum,
P. pulmonicola,
and
P. apista, mainly associated with clinical isolates recovered
from CF patients, and
P. norimbergensis (formerly
Burkholderia norimbergensis), rarely isolated from the environment and from
human clinical specimens. Four
Pandoraea genomospecies, containing
one strain each, were also described (
9). The misidentification
of
Ralstonia and
Pandoraea species as organisms belonging to
the
B. cepacia complex (Bcc) is fraught with consequences since
the recovery of a Bcc organism in a CF patient leads to strict
infection control measures in order to reduce patient-to-patient
spread, and possibly to exclusion from lung transplantation.
At present, the prevalence, patient-to-patient transmissibility,
and clinical impact of
Ralstonia and
Pandoraea organisms in
CF patients are unknown and cannot be evaluated if they are
badly recognized in the clinical microbiology laboratory. Thus,
an accurate identification of these species is essential. Unfortunately,
the usual manual and automated phenotypic identification methods
are not satisfactory (
1,
14,
15). The aim of this study was
to determine whether amplified ribosomal DNA restriction analysis
(ARDRA), already successfully applied to the identification
of
Burkholderia species (
13), could be used for
Ralstonia and
Pandoraea species.
The type strains of the following Ralstonia and Pandoraea species were tested: R. solanacearum, R. eutropha, R. campinensis, R. metallidurans, R. basilensis, R. pickettii, R. mannitolilytica, R. gilardii, R. taiwanensis, and R. paucula and P. pnomenusa, P. sputorum, P. pulmonicola, P. apista, and P. norimbergensis. As R. solanacearum is known to be a heterogeneous species, several strains, representative of races 1, 2, and 3, kindly provided by Christian Boucher (Centre National de la Recherche Scientifique-Institut National de la Recherche Agronomique, Castanet-Tolosan, France) were included. The other reference strains were obtained from international culture collections. Five clinical isolates recovered from the sputum of CF patients and transmitted to the French Observatoire Cepacia/Vaincre la Mucoviscidose were also analyzed. These isolates had been grown on B. cepacia-selective media and were resistant to colistin, aminoglycosides, ticarcillin, and aztreonam but did not belong to the Burkholderia genus according to ARDRA. Two of these isolates, kindly provided by A. Ferroni, had been identified as R. mannitolilytica by use of 16S rRNA sequencing (10). The bacterial strains studied and their sources are listed in Table 1.
The restriction fragment length polymorphism (RFLP) analysis
of amplified 16S rDNA was performed as previously described
(
13). Briefly, the primers fD1 (5'-CCGAATTCGTCGACAACAGAGTTTGATCCTGGCTCAG-3')
and rD1 (5'-CCCGGGATCCAAGCTTAAGGAGGTGATCCAGCC-3') were used
to amplify approximately 1,500 bp within the 16S rRNA gene.
The PCR products were digested with the following endonucleases:
AluI,
CfoI,
DdeI,
MspI,
NciI, and
BssKI.
Some of the restriction profiles obtained are shown in Fig. 1, and ARDRA results are summarized in Table 1. The previously published results (13) obtained for the two main Bcc species involved in cystic fibrosis, i.e., B. cepacia genomovar III and B. multivorans, are included in Table 1 for comparison. The 14 Ralstonia type and reference strains tested, representing 10 species, were classified in 12 ARDRA groups; the 5 R. solanacearum strains were classified in 3 ARDRA groups, and one of the strains belonging to race 1 was not discriminated from the representative strain of race 2 tested. The type strains of all the Ralstonia species included in this study harbored specific ARDRA patterns. The five Pandoraea type strains tested were classified in three ARDRA groups; thus, P. pnomenusa and P. sputorum on one hand and P. pulmonicola and P. apista on the other hand harbor the same RFLP profiles. The five clinical strains tested presented the same RFLP profiles as the R. mannitolilytica type strain. Finally, the ARDRA patterns clearly differentiate Ralstonia and Pandoraea species from Burkholderia species, as well as from other nonfermenting gram-negative bacilli frequently recovered from patients with CF, such as Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Achromobacter xylosoxidans (data not shown). The prevalence of Ralstonia species in patients with CF is probably low but may be underestimated due to misidentification. Coenye et al. recently reported that 42 of about 4,000 bacterial isolates collected from American CF patients and sent to the Burkholderia cepacia Research Laboratory and Repository (University of Michigan) belonged to the genus Ralstonia (8), with R. mannitolilytica being the most prevalent species (25 out of 42 isolates). In a French pediatric CF center, R. mannitolilytica was recovered from 2 out of 259 patients (10). Finally, 5 clinical isolates out of 247 nonredundant isolates recovered from 243 French CF patients and collected by the Observatoire Cepacia/Vaincre la Mucoviscidose, including the two isolates mentioned above, were identified as R. mannitolilytica in the present study. The pathogenic potential of this species is not clear; however, chronic colonization is possible. Pandoraea species have been recovered from CF patients in Canada, Denmark, Brazil, the United States, and the United Kingdom, but to our knowledge there are no available epidemiological data concerning the prevalence of these organisms in CF patients.
Phenotypic tests for
Ralstonia and
Pandoraea species can be
misleading: confusion of
Ralstonia sp. with
Burkholderia sp.,
Pseudomonas sp., and
S. maltophilia (
8,
10) and of
Pandoraea sp. with
Burkholderia sp. and
Ralstonia sp. has been reported
(
4). Thus, molecular methods are necessary for an accurate diagnosis.
16S rRNA gene sequencing (
10) is widely applicable to any problematic
isolate but requires a sequencer; 16S ribosomal DNA-based genus-
and/or species-specific PCR has been developed for
R. mannitolilytica and
R. pickettii (
8) and for
Pandoraea species (
7). Analysis
of the
gyrB gene seems promising for the identification of
Pandoraea species (
6). The ARDRA method tested in this study, though unable
to separate all
Pandoraea species, proves to be a useful identification
tool; it requires the constitution of a data bank of profiles
but has the advantage of being equally applicable to the main
organisms growing on
B. cepacia-selective media, i.e.,
Burkholderia,
Ralstonia, and
Pandoraea.

ACKNOWLEDGMENTS
This study was supported by the Université Paul-Sabatier,
Toulouse III, France and by the French CF Association Vaincre
La Mucoviscidose.
We thank A. Ferroni (Hôpital Necker, Paris), H. Monteil (Institut de Bactériologie, Strasbourg), P. Plessis (Centre Hospitalier des Pays-de-Morlaix), and J. Thubert (Centre de Perharidy, Roscoff) for providing clinical strains.

FOOTNOTES
* Corresponding author. Mailing address: Laboratoire de Bactériologie-Hygiène, Hôpital Rangueil-TSA 50032, 31059 Toulouse Cedex 9, France. Phone: 33-(0)5-61-32-28-28. Fax: 33-(0)5-61-32-26-20. E-mail:
segonds{at}cict.fr.


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Journal of Clinical Microbiology, July 2003, p. 3415-3418, Vol. 41, No. 7
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.7.3415-3418.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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