JAC Advance Access originally published online on December 12, 2005
Journal of Antimicrobial Chemotherapy 2006 57(2):368-369; doi:10.1093/jac/dki450
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Correspondence |
TEM-21 extended-spectrum ß-lactamase in a clinical isolate of Alcaligenes faecalis from a nursing home
Laboratoire de Microbiologie, Faculté de Pharmacie, EA 525, Université de Bordeaux 2, Bordeaux, France
* Corresponding author. Tel: +33-5-57-57-10-75; Fax: +33-5-56-90-90-72; E-mail: veronique.dubois{at}bacterio.u-bordeaux2.fr
Keywords: antibiotic resistance , horizontal gene transfer , saprophytic organisms
Sir,
Alcaligenes faecalis is an aerobic, glucose-non-fermenting, Gram-negative bacillus, ubiquitous in soil and water but rarely isolated from humans.1 Most infections caused by this bacterium have been nosocomial, often related to contamination of hospital equipment or fluids and have occurred in immunocompromised hosts.2,3 Most strains appeared to display multiple resistance to numerous antibiotics, including ß-lactams (amoxicillin, ticarcillin and aztreonam), aminoglycosides and quinolones but were susceptible to combinations of amoxicillin or ticarcillin plus clavulanic acid and to the cephalosporins.2 The only extended-spectrum ß-lactamase (ESBL) described in A. faecalis has been PER-1, an enzyme previously found in Pseudomonas aeruginosa, Salmonella and Acinetobacter.3 In this study, we report a TEM-type ESBL, commonly encountered among Enterobacteriaceae in the area of Bordeaux,4 in a clinical strain of A. faecalis from a nursing home.
The A. faecalis strain Af1930 was isolated in 2002 from the urine of an 89-year-old woman living in a nursing home. This patient was paralysed and aphasic after vascular brain damage, and carried urinary, gastrostomy and colostomy catheters. Prior to Af1930 isolation, she received several alternate courses of intravenous ceftriaxone and intramuscular colistin. Identification to the species level was confirmed by amplification and sequencing of the rrs gene (Institut Pasteur, Paris, France). By the disc diffusion method and MIC determination using the agar dilution method in Mueller–Hinton medium (http://www.sfm.asso.fr), Af1930 was resistant to aminopenicillins, carboxypenicillins, cefalotin, cefotaxime, ceftazidime and cefepime but susceptible to their combination with ß-lactamase inhibitors, cefoxitin and imipenem (Table 1). The presence of an ESBL was easily detected by a marked synergy between clavulanic acid and ceftazidime or cefotaxime.5 The strain also exhibited resistance to kanamycin, gentamicin, tobramycin, netilmicin, amikacin, chloramphenicol, co-trimoxazole, tetracycline, fosfomycin and fluoroquinolones. By isoelectric focusing, Af1930 produced two ß-lactamases of pI 6.4 and >8, respectively. Amplification with primers specific for blaTEM,6 and subsequent sequencing revealed the presence of the blaTEM-21 gene that encodes a ß-lactamase of pI 6.4.7 We have recently reported an endemic situation in this nursing home owing to the dissemination of TEM-21-producing strains of P. aeruginosa and enterobacteria, and a TEM-21-encoding plasmid.4,6 Conjugation experiments by a filter mating technique between the clinical strain Af1930 and the azide-resistant Escherichia coli C600, the rifampicin- and nalidixic acid-resistant E. coli K12 or the rifampicin-resistant mutant P. aeruginosa ATCC 27853 as recipients, did not yield any ESBL-producing transconjugant (<10–8). Plasmid DNA extract showed the presence of a large plasmid, but ESBL transfer by electroporation into E. coli DH5
remained unsuccessful. Moreover, the restriction profile of this large plasmid, obtained with the EcoRI enzyme, was different from that of the epidemic plasmid encountered in the enterobacteria strains of the nursing home (data not shown). Finally, a Southern-blot hybridization using a blaTEM probe gave a smear of high molecular weight with the unrestricted whole-cell DNA, and an absence of signal with the unrestricted or NruI-digested plasmid DNA of Af1930 (data not shown). These data strongly argued for a chromosomal location of the blaTEM-21 gene in A. faecalis Af1930 as in the epidemic P. aeruginosa strain.6 Indeed, differences in origins of replication may lead to the elimination of plasmids from Enterobacteriaceae in glucose-non-fermenting, Gram-negative bacilli. Therefore, the persistence of the resistance genes in strains of P. aeruginosa or A. faecalis may have required their chromosomal integration. Using several laboratory-designed primers [C6T7, C6T7bis, aac(3)-IIb, TnpA4R and IRL4321],6 DNA amplifications showed that in Af1930, as in enterobacteria, the blaTEM-21 gene was part of a Tn801 transposon disrupted by IS4321 and adjacent to the aac(3)-II gene. In addition, the aac(6')-I gene, present on the resistance plasmid epidemic among enterobacteria, was detected by PCR in Af1930, suggesting the complete chromosomal integration of the plasmid in Af1930, in contrast with the P. aeruginosa strains, in which this gene was lacking. In the previous report on the PER-1-producing A. faecalis, the ESBL-encoding gene was associated with a transposon-like element of the Tn3 family located on a large non-conjugative plasmid and the acquisition of the blaPER-1 determinant was probably related to an outbreak of PER-1-expressing P. aeruginosa in the same hospital.3,8
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The present work is the first report of a TEM-type ESBL in A. faecalis, highlighting the possible spread of these enzymes from Enterobacteriaceae to saprophytic and taxonomically distant Gram-negative bacilli, when the epidemic pressure becomes intense and providing that the epidemic plasmid may persist. However, chromosomal insertion should allow limited further dissemination of the ESBL.
Transparency declarations
None to declare.
Acknowledgements
This work was supported by grants from the Ministère de l'Education Nationale et de la Recherche (EA-525), Université de Bordeaux 2, Bordeaux, France.
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