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Antimicrobial Agents and Chemotherapy, April 2007, p. 1179-1184, Vol. 51, No. 4
0066-4804/07/$08.00+0     doi:10.1128/AAC.01101-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Population Structure and Resistance Genes in Antibiotic-Resistant Bacteria from a Remote Community with Minimal Antibiotic Exposure{triangledown}

Lucia Pallecchi,1 Chiara Lucchetti,1 Alessandro Bartoloni,2 Filippo Bartalesi,2 Antonia Mantella,2 Herlan Gamboa,3 Alessandra Carattoli,4 Franco Paradisi,2 and Gian Maria Rossolini1*

Dipartimento di Biologia Molecolare, Laboratorio di Fisiologia e Biotecnologia dei Microrganismi, Università di Siena, Siena, Italy,1 Dipartimento Area Critica Medico Chirurgica, Clinica Malattie Infettive, Università di Firenze, Florence, Italy,2 Red de Salud Cordillera, Servicio Departamental de Santa Cruz, Camiri, Bolivia,3 Dipartimento di Malattie Infettive, Parassitarie e Immunomediate, Istituto Superiore di Sanità, Rome, Italy4

Received 31 August 2006/ Returned for modification 1 November 2006/ Accepted 20 November 2006

In a previous study, we detected unexpectedly high levels of acquired antibiotic resistance in commensal Escherichia coli isolates from a remote Guaraní Indian (Bolivia) community with very low levels of antibiotic exposure and limited exchanges with the exterior. Here we analyzed the structure of the resistant E. coli population from that community and the resistance mechanisms. The E. coli population (113 isolates from 72 inhabitants) showed a high degree of genetic heterogeneity, as evidenced by phylogenetic grouping (77% group A, 10% group B1, 8% group D, 5% group B2) and genotyping by randomly amplified polymorphic DNA (RAPD) analysis (44 different RAPD types). The acquired resistance genes were always of the same types as those found in antibiotic-exposed settings [blaTEM, blaPSE-1, catI, cmlA6, tet(A), tet(B), dfrA1, dfrA7, dfrA8, dfrA17, sul1, sul2, aphA1, aadA1, aadA2, aadA5, aadB, and sat-1]. Class 1 and class 2 integrons were found in 12% and 4% of the isolates, respectively, and harbored arrays of gene cassettes similar to those already described. The cotransferability of multiple-resistance traits was observed from selected isolates and was found to be associated with resistance conjugative plasmids of the F, P, and N types. Overall, these data suggest that the resistance observed in this remote community is likely the consequence of the dissemination of resistant bacteria and resistance genes from antibiotic-exposed settings (rather than of an independent in situ selection) which involved both the clonal expansion of resistant strains and the horizontal transfer/recombination of mobile genetic elements harboring resistance genes.

* Corresponding author. Mailing address: Dipartimento di Biologia Molecolare, Laboratorio di Fisiologia e Biotecnologia dei Microrganismi, Università di Siena, Policlinico Santa Maria alle Scotte, 53100 Siena, Italy. Phone: 39 0577 233327. Fax: 39 0577 233334. E-mail: rossolini{at}unisi.it

{triangledown} Published ahead of print on 12 January 2006.

Antimicrobial Agents and Chemotherapy, April 2007, p. 1179-1184, Vol. 51, No. 4
0066-4804/07/$08.00+0     doi:10.1128/AAC.01101-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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