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Journal of Clinical Microbiology, December 2003, p. 5747-5749, Vol. 41, No. 12
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.12.5747-5749.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
DNA Fingerprinting of Ralstonia paucula by Infrequent-Restriction-Site PCR and Randomly Amplified Polymorphic DNA Analysis
Didier Moissenet,1 Hoang Vu-Thien,1* Yahia Benzerara,2 and Guillaume Arlet2,3
Service de Microbiologie, Hôpital d'enfants Armand-Trousseau AP-HP,1
Service de Microbiologie, Hôpital Tenon AP-HP,2
EA2392, UFR Saint-Antoine, Université Paris VI, Paris, France3
Received 21 April 2003/
Returned for modification 11 July 2003/
Accepted 18 September 2003

ABSTRACT
Ralstonia paucula (formerly CDC group IV c-2) is an environmental
organism that can cause serious human infections, occasionally
clusters of nosocomial infections. In the present work, 26 strains
of
R. paucula (4 from the American Centers for Disease Control
and Prevention collection, 10 from the Belgian Laboratorium
voor Microbiologie [LMG] collection, and 12 French clinical
isolates) were analyzed with infrequent-restriction-site PCR
and randomly amplified polymorphic DNA analysis. Both techniques
accurately distinguished between collection strains. Two close
patterns obtained for all the French isolates suggested a clonal
strain. Two LMG collection strains originating from human sources
in the United States also showed patterns close to those of
French isolates.

TEXT
Since 1995, the taxonomy of many gram-negative environmental
bacilli has changed (
3,
14).
Ralstonia paucula sp. nov., formerly
CDC group IV c-2, was assigned to the genus
Ralstonia in 1999
(
7,
12). Isolated from pool water, groundwater, bottled mineral
water (
2,
4,
9), and many clinical specimens,
R. paucula, despite
its low pathogenicity, is now recognized as an opportunist pathogen
that can generate serious infections, such as septicemia, peritonitis,
abscesses, etc., especially in immunocompromised patients (
1,
8,
10). Furthermore, though less often isolated than
Ralstonia pickettii,
R. paucula can cause clusters of nosocomial infections
(
8). Treatment of such infections was mainly based on the use
of beta-lactams such as cefotaxime, ceftriaxone, piperacillin,
and imipenem (
1,
8,
10).
In 1996, two clusters of CDC group IV c-2 septicemia at the Trousseau Children's Hospital were reported (8). Comparison between these isolates and eight other blood isolates obtained from six distinct hospitals in Paris area by use of randomly amplified polymorphic DNA (RAPD) analysis showed a single pattern, and consequently the isolates could not be distinguished (8). Genotyping with pulsed-field gel electrophoresis was unsuccessful, owing to DNA degradation probably caused by strong DNase activity, which was not blocked by boiling or formaldehyde fixation (7). In contrast, parallel processing of four reference strains obtained from the Centers for Disease Control and Prevention showed four distinct patterns with both RAPD analysis and pulsed-field gel electrophoresis (8). Finally, two other typing methods, PCR ribotyping and PCR restriction of the ribosomal intergenic spacer region, were unsuccessful in typing French R. paucula clinical isolates (6). A recently described method referred to as the infrequent-restriction-site PCR (IRS-PCR) assay (5, 11) has not previously been applied to Ralstonia. In this study, DNA fingerprinting with IRS-PCR, as well as RAPD, was used to distinguish between R. paucula strains from a large collection of strains kindly provided by Peter Vandammme (Laboratorium voor Microbiologie [LMG], Ghent, Belgium) (12).
Four CDC group IV c-2 strains (G6817, G3900, G608 and F4862) and 10 strains of R. paucula from the LMG collection (LMG 3244, LMG 3245, LMG 3317, LMG 3318, LMG 3319, LMG 3320, LMG 3413, LMG 3517, LMG 3518, and LMG 15544) were studied (Table 1). Twelve R. paucula blood isolates from the Trousseau Children's Hospital and five other French hospitals were also studied. These institutions are all located in the Paris area but in quite distinct districts.
IRS-PCR.
The
XbaI adaptors, AX1 (5'-CTA GTA CTG GCA GAC TCT-3') and AX2
(5'-GCC AGT A-3'), were constructed as previously described
by Mazurek et al. (
5). The
PstI adaptors PS1 (5'-GAC TCG ACT
CGC ATG CA-3') and PS2 (5'-TGC GAG T-3') were constructed as
previously described by Riffard et al. (
11). The adaptors, AX1
and AX2, or PS1 and PS2, were mixed in equimolar amounts and
were allowed to anneal as the mixture cooled from 80 to 4°C.
Oligonucleotides PX-A, PX-T, PX-G, and PX-C (5'-AGA GTC TGC
CAG TAC TAG AS-3' [S = A, T, G, or C]) were used as primers
in PCR. DNA was prepared with the QIAamp DNA Mini Kit (Qiagen,
Hilden, Germany) and was digested with 10 U of
PstI and 10 U
of
XbaI for 1 h at 37°C. T4 DNA ligase, ATP, and the AX
and PS adaptors were added, and the mixture was incubated at
16°C for 1 h and then at 65°C for 15 min to inactivate
T4 DNA ligase. The sample was digested with 5 U of
PstI and
5 U of
XbaI at 37°C for 30 min to cleave any restriction
sites reformed by ligation. Amplification was performed in a
GeneAmp PCR System 9700 (Perkin-Elmer, Branchburg, N.J.) with
an amplification profile that consisted of an initial denaturation
step at 94°C for 5 min and then 30 cycles with denaturation
at 94°C for 30 s, primer annealing at 60°C for 30 s,
extension at 72°C for 90 s, and a final elongation at 72°C
for 5 min.
RAPD procedure.
The universal primer M13 (5'-TTATGTAAAACGACGGCCAGT-3') was used (8, 13). DNA was amplified in 50 µl of a solution containing 50 ng of DNA, 3 µM primer, 2.5 U of AmpliTaq DNA polymerase, the four deoxynucleoside triphosphates (400 µM each), 4 mM MgCl2, 10 mM Tris-HCl (pH 8.3), and 50 mM KCl. The mixtures were subjected to 35 cycles of amplification (95°C for 1 min, 55°C for 1 min, and 72°C for 1 min) in a thermocycler (Perkin-Elmer Cetus, Norwalk, Conn.). In a further cycle, the first denaturation step at 95°C lasted for 3 min and the incubation at 72°C lasted for 5 min.
With IRS-PCR, similar results were obtained regardless of what primer (PX-A, PX-T, PX-G, or PX-C) was used together with PS1. PX-A patterns (six to eight bands ranging in size from 900 to 110 bp) are shown in Fig. 1. IRS-PCR electrophoretic patterns enabled one to distinguish between the four Centers for Disease Control and Prevention strains, while all the French clinical isolates showed the same pattern, except for one strain that showed a one-band difference (Fig. 1). Only nine different patterns were observed over the 10 strains from the LMG collection; namely, two strains (LMG 3245 and LMG 3318) showed the same pattern, this one being surprisingly close to the major pattern of French isolates, named the Trousseau IRS-PCR pattern (Fig. 1).
RAPD was as efficient as IRS-PCR in distinguishing between
R. paucula strains (three to seven bands ranging in size from 1,114
to 190 bp). It also distinguished between the four Centers for
Disease Control and Prevention strains and showed a major pattern
(named Trousseau RAPD pattern) for six of the eight French isolates.
The two remaining others showed one-band differences (Fig.
2).
Nine different patterns were observed for the 10 strains from
the LMG collection; as a matter of fact, the two strains (LMG
3245 and LMG 3318) already reported to be slightly different
with IRS-PCR showed here a one-band difference. These two similar
patterns were also close to the Trousseau RAPD pattern (Fig.
2). One CDC strain's (G6817) pattern appeared similar to those
of French isolates (Fig.
2). This showed the value of using
several primers in the RAPD technique. We have established a
precedent by using six primers and by showing distinct patterns
for CDC and French isolates, especially with the following primer:
5'-TCACGATGCA-3' (
7).
A relationship was therefore suggested between three strains
that we did not expect to be related, namely, the two LMG strains
originating from different human sources in the United States
and the French strain representative of various isolates obtained
between 1993 and 1995 from different hospitals in the Paris
area.
IRS-PCR was more time consuming and labor intensive than RAPD. Though a higher number of bands was observed on the IRS-PCR patterns than on the RAPD patterns, both techniques used in this study yielded well-resolved and easily compared fragment patterns in the fingerprinting of R. paucula strains.

ACKNOWLEDGMENTS
We thank Peter Vandamme (LMG) for providing us with 10
R. paucula strains (LMG 3244, LMG 3245, LMG 3317, LMG 3318, LMG 3319, LMG
3320, LMG 3413, LMG 3517, LMG 3518, and LMG 15544).

FOOTNOTES
* Corresponding author. Mailing address: Service de Microbiologie, Hôpital d'enfants Armand-Trousseau, 26, avenue du Dr Arnold-Netter, 75571 Paris Cedex 12, France. Phone: 33 1 44 73 53 28. Fax: 33 1 44 73 62 88. E-mail:
hoang.vuthien{at}trs.ap-hop-paris.fr.


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Journal of Clinical Microbiology, December 2003, p. 5747-5749, Vol. 41, No. 12
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.12.5747-5749.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.