Characterization of Small ColE-Like Plasmids Mediating Widespread Dissemination of the qnrB19 Gene in Commensal Enterobacteria

Antimicrobial Agents and Chemotherapy, February 2010, p. 678-682, Vol. 54, No. 2
Copyright © 2010, American Society for Microbiology. All Rights Reserved.

Lucia Pallecchi,1 Eleonora Riccobono,1 Samanta Sennati,1 Antonia Mantella,2 Filippo Bartalesi,2 Christian Trigoso,3 Eduardo Gotuzzo,4 Alessandro Bartoloni,2 and Gian Maria Rossolini1,5*

Dipartimento di Biologia Molecolare, Sezione di Microbiologia, Università di Siena,1 Dipartimento dei Servizi, U. O. Microbiologia e Virologia, Azienda Ospedaliera-Universitaria Senese, Siena, Italy,5 Dipartimento Area Critica Medico Chirurgica, Clinica Malattie Infettive, Università di Firenze, Florence, Italy,2 Instituto Nacional de Laboratorios de Salud INLASA, La Paz, Bolivia,3 Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru4

Received 16 August 2009/ Returned for modification 9 November 2009/ Accepted 1 December 2009

In this work, we have characterized two small ColE-like plasmids (pECY6-7, 2.7 kb in size, and pECC14-9, of 3.0 kb), encoding the QnrB19 quinolone resistance determinant, that were carried by several clonally unrelated quinolone-resistant commensal Escherichia coli strains isolated from healthy children living in different urban areas of Peru and Bolivia. The two plasmids are closely related to each other and carry the qnrB19 gene as the sole resistance determinant, located in a conserved genetic context between the plasmid RNAII sequence (which controls plasmid replication) and the plasmid Xer site (involved in plasmid dimer resolution). ISEcp1-like or other putative insertion sequences are not present in the qnrB19-flanking regions or elsewhere on the plasmids. Since we previously observed a high prevalence (54%) of qnrB genes in the metagenomes of commensal enterobacteria from the same population of healthy children, the presence of pECY6-7- and pECC14-9-like plasmids in those qnrB-positive metagenomes was investigated by PCR mapping. Both plasmids were found to be highly prevalent (67% and 16%, respectively) in the qnrB-positive metagenomes, suggesting that dissemination of these small plasmids played a major role in the widespread dissemination of qnrB genes observed in commensal enterobacteria from healthy children living in those areas.
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* Corresponding author. Mailing address: Dipartimento di Biologia Molecolare, Sezione di Microbiologia, Università di Siena, Policlinico Santa Maria alle Scotte, 53100 Siena, Italy. Phone: 39 0577 233455. Fax: 39 0577 233870. E-mail: rossolini@unisi.it
Published ahead of print on 14 December 2009.