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Antimicrobial Agents and Chemotherapy, August 1999, p. 2097-2098, Vol. 43, No. 8
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
LETTERS TO THE EDITOR
Plasmid-Mediated Coresistance to Streptogramins and
Vancomycin in Enterococcus faecium HM1032
 |
LETTER |
Enterococcus faecium has emerged as a major
cause of nosocomial infections. Correspondingly, this species has
become increasingly resistant to a broad range of antimicrobial agents,
including aminoglycosides, penicillins, and glycopeptides
(4). Quinupristin-dalfopristin, an injectable streptogramin,
is proposed as an alternative drug for severe infections caused by
multiply resistant E. faecium and in many cases could
represent the only therapy available (3).
We have isolated from urine a strain of E. faecium, HM1032,
which was resistant to both vancomycin and quinupristin-dalfopristin, and we have studied the localization of the genetic determinants for
these resistances. E. faecium HM1032 was resistant to
erythromycin (MIC > 128 µg/ml), quinupristin-dalfopristin
(MIC = 16 µg/ml), vancomycin (MIC >128 µg/ml), and
tetracycline. We found that resistance to macrolides and vancomycin was
related to the presence of an ermAM (ermB)-like
gene and a vanA gene, respectively, as shown by PCR
experiments (2, 6). Resistance to quinupristin-dalfopristin was due to inactivation of quinupristin and dalfopristin (MICs = 64 µg/ml), as suggested by a microbiological screen test, Gots' test, and confirmed in PCR experiments by amplification of
vgb- and satA-like genes responsible for
acetylation and hydrolysis of quinupristin and dalfopristin,
respectively. The nucleotide sequences of amplicons were nearly
identical to those of the prototype satA and vgb
genes (1, 5).
The resistances could not be transferred by mating on filters to
E. faecium HM1070, a plasmid-free recipient strain, except for tetracycline resistance, which transferred with a frequency of
10
6 per donor colony. Transformation of E. faecium HM1070 with plasmid extracts of E. faecium
HM1032 yielded clones coresistant to vancomycin, quinupristin-dalfopristin (MIC = 8 µg/ml), and erythromycin.
However, the transformants inactivated dalfopristin but not
quinupristin. One of the transformants, E. faecium HM1070SR,
was studied further, and PCR experiments indicated that the strain
contained the vanA, ermAM, and satA
genes but not the vgb gene.
Total DNA, plasmid DNA of E. faecium HM1032, and plasmid DNA
of E. faecium HM1070SR were analyzed by agarose gel
electrophoresis and hybridization with vanA,
ermAM, vgb, and satA probes (Fig. 1). E. faecium HM1032
contained at least six plasmids, three of which were present in
E. faecium HM1070SR. The ermAM, satA,
and vanA genes were localized on the same large plasmid
(>60 kb), while the vgb gene was apparently chromosomal in
the wild-type strain (lack of hybridization to plasmid bands with
hybridization to the region with linearized DNA, including fragments of
chromosomal DNA) and absent from the transformant. After plasmid
digestion with EcoRI, vanA, satA, and
ermAM probes hybridized to EcoRI fragments, of
5.5, 10, and 10 kb, respectively (data not shown).
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FIG. 1.
Analysis of non-digested genomic DNA (lane 1) and
plasmid DNA (lane 2) from E. faecium HM1032 and of
nondigested plasmid DNA from the transformant E. faecium
HM1070SR (lane 3) by agarose gel electrophoresis and hybridization. (A)
Agarose gel electrophoresis of DNA; (B to E) hybridization to
ermAM, satA, vanA, and vgb
probes, respectively. Linear (chromosomal) DNA is indicated on the left
of the gel (Chr). ermAM, satA, and
vanA probes hybridized to the same large plasmid; the
vgb probe hybridized to the chromosomal DNA of E. faecium HM1032.
|
|
Although uncommon, quinupristin-dalfopristin resistance in
glycopeptide-resistant E. faecium has already been reported
for human and animal isolates from Germany, the United Kingdom, and the
United States (3, 7, 8). The presence of genes responsible for glycopeptide and streptogramin resistance linked on the same plasmid is an additional cause of concern if this plasmid happened to
disseminate. Although we were unable to transfer by conjugation this
resistance plasmid to a recipient strain, transformation experiments
showed that the combination of genes for resistance to vancomycin and
streptogramins borne by this plasmid was sufficient to confer
resistance to both antibiotics.
| |
FOOTNOTES |
*
Phone: (33) 2 31 06 45 72
Fax: (33) 2 31 06 45 73
E-mail: leclercq-r{at}chu-caen.fr
| |
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| | | | |
Bülent Bozdogan
Roland Leclercq*
Service de Microbiologie
Hôpital Côte de Nacre
Université de Caen
14033 Caen
France
|
| | | | |
Alain Lozniewski
Michèle Weber
Laboratoire de Bactériologie
Hôpital Central
Centre Hospitalier et Universitaire
54035 Nancy
France
|
Antimicrobial Agents and Chemotherapy, August 1999, p. 2097-2098, Vol. 43, No. 8
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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