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Antimicrobial Agents and Chemotherapy, August 2007, p. 2720-2725, Vol. 51, No. 8
0066-4804/07/$08.00+0     doi:10.1128/AAC.00026-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Rapid Dissemination and Diversity of CTX-M Extended-Spectrum ß-Lactamase Genes in Commensal Escherichia coli Isolates from Healthy Children from Low-Resource Settings in Latin America

Dipartimento di Biologia Molecolare, Sezione di Microbiologia, Università di Siena, Siena, Italy,¹ Dipartimento Area Critica Medico Chirurgica, Clinica Malattie Infettive, Università di Firenze, Florence, Italy,² Distrito de Salud Cordillera, Departamento Santa Cruz, Camiri, Bolivia,³ Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru,⁴ Department of Microbiology and Tumor Biology-MTC, Clinical Microbiology, Karolinska Institut, Stockholm, Sweden⁵

Received 9 January 2007/ Returned for modification 1 March 2007/ Accepted 24 May 2007

A survey carried out in 2005 among members of a healthy population of children living in Bolivia and Peru revealed that fecal carriage of Escherichia coli strains resistant to expanded-spectrum cephalosporins was remarkably increased compared to that observed in the same settings in 2002 (1.7% in 2005 versus 0.1% in 2002). In this work, we demonstrated that this phenomenon was mainly related to the dissemination of CTX-M-type extended-spectrum ß-lactamase (ESBL) determinants among commensal E. coli strains. Of 50 ESBL-producing isolates collected in the 2005 survey, 44 harbored a CTX-M-type and 6 an SHV-type (SHV-2 or SHV-12) ESBL. Compared to 2002 results, an increased diversity of CTX-M-type ESBLs was also observed: members of the CTX-M-1 group (CTX-M-15) emerged in Bolivia (where only CTX-M-2 was observed in 2002), while members of the CTX-M-9 group (CTX-M-14 and CTX-M-24) emerged in Peru (where only CTX-M-15 and CTX-M-2 were observed in 2002). A new CTX-M-2 variant named CTX-M-56 was also detected. Molecular characterization of the CTX-M-producing isolates and gene transfer experiments suggested that different mechanisms could be involved in the spreading of different CTX-M group determinants and revealed that additional resistance determinants for non-ß-lactam antibiotics were preferentially carried by plasmids encoding certain CTX-M variants (CTX-M-15 and variants of the CTX-M-2 group). Three CTX-M-15-encoding conjugative plasmids from Peruvian isolates carried the new fluoroquinolone resistance gene aac(6')-Ib-cr. To our best knowledge, this is the first report of the detection of aac(6')-Ib-cr in Latin America.

Published ahead of print on 4 June 2007.