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Next Article 

Applied and Environmental Microbiology, May 2009, p. 2999-3006, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02143-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Relatedness of Escherichia coli Strains with Different Susceptibility Phenotypes Isolated from Swine Feces during Ampicillin Treatment{triangledown}

D. Bibbal,1 V. Dupouy,1 M. F. Prère,2 P. L. Toutain,1 and A. Bousquet-Mélou1*

UMR181 Physiopathologie et Toxicologie Expérimentales, INRA, ENVT, Ecole Nationale Vétérinaire de Toulouse, 23 Chemin des Capelles, BP 87 614, 31076 Toulouse Cedex 3, France,1 UMR5100 Microbiologie et Génétique Moléculaires, CNRS, UPS, Laboratoire de Microbiologie et Génétique Moléculaires, Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse Cedex, France2

Received 16 September 2008/ Accepted 26 February 2009

The aim of this study was to examine the dynamics of the development of resistance in fecal Escherichia coli populations during treatment with ampicillin for 7 days in pigs. Before treatment, only 6% of the isolates were ampicillin resistant, whereas more than 90% of the isolates were resistant after days 4 and 7 of treatment. Ampicillin-resistant E. coli isolates were mainly multiresistant, and 53% of the isolates from the treated pigs had one phenotype that included resistance to six antibiotics (ampicillin, chloramphenicol, sulfonamides, tetracycline, trimethoprim, and streptomycin) at day 7. Determination of the frequency of the four phylogenetic groups showed that there was a shift in the E. coli population in ampicillin-treated pigs; before treatment 75% of the isolates belonged to phylogroup B1, whereas at day 7 85% of the isolates belonged to phylogroup A. Pulsed-field gel electrophoresis (PFGE) typing revealed that ampicillin treatment selected ampicillin-resistant isolates with genotypes which were present before treatment. Comparison of antimicrobial phenotypes and PFGE genotypes showed that resistance traits were disseminated by vertical transmission through defined strains. One PFGE genotype, associated with the six-antibiotic-resistant phenotype and including a specific combination of resistance determinants, was predominant among the ampicillin-resistant strains before treatment and during treatment. These data indicate that ampicillin administration selected various ampicillin-resistant isolates that were present in the digestive tract before any treatment and that E. coli isolates belonging to one specific PFGE genotype encoding resistance to six antibiotics became the predominant strains as soon as ampicillin was present in the digestive tract.

* Corresponding author. Mailing address: UMR181 Physiopathologie et Toxicologie Expérimentales, INRA, ENVT, Ecole Nationale Vétérinaire de Toulouse, 23 Chemin des Capelles, BP 87 614, 31076 Toulouse Cedex 3, France. Phone: 33 (0) 561 193 925. Fax: 33 (0) 561 193 917. E-mail: a.bousquet-melou{at}envt.fr

{triangledown} Published ahead of print on 6 March 2009.

Applied and Environmental Microbiology, May 2009, p. 2999-3006, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02143-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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