AEM Accepts, published online ahead of print on 8 June 2007

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Appl. Environ. Microbiol. doi:10.1128/AEM.00252-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Impact of three ampicillin dosage regimens on selection of ampicillin resistance in Enterobacteriaceae and excretion of bla_TEM genes in swine feces

D. Bibbal, V. Dupouy, J. P. Ferré, P. L. Toutain, O. Fayet, M. F. Prère, and A. Bousquet-Mélou^*

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

^* To whom correspondence should be addressed. Email: a.bousquet-melou{at}envt.fr.

The aim of this study was to assess the impact of three ampicillin dosage regimens on ampicillin resistance among Enterobacteriaceae recovered from swine feces using phenotypic and genotypic approaches. Phenotypically, ampicillin resistance was determined from the percentage of resistant Enterobacteriaceae and MICs of E. coli isolates. The pool of ampicillin resistance genes was also monitored by quantification of bla_TEM genes, which code for the most frequently produced -lactamases in Gram-negative bacteria, using a newly-developed real-time PCR assay. Ampicillin was administered intramuscularly and by oral route to fed or fasted pigs for 7 days at 20 mg/kg. The average percentage of resistant Enterobacteriaceae before treatment was between 2.5% and 12% and bla_TEM genes quantities were below 10⁷ copies/g of feces. By days four and seven, the percentage of resistant Enterobacteriaceae exceeded 50% in all treated groups, with some highly resistant strains (MIC>256µg/mL). In the control group, bla_TEM genes quantities fluctuated between 10⁴ - 10⁶ copies/g of feces, whereas they fluctuated between 10⁶-10⁸ and 10⁷-10⁹ copies/g of feces for intramuscular and oral routes, respectively. Whereas phenotypic evaluations did not discriminate between the three ampicillin dosage regimens, bla_TEM genes quantification was able to differentiate between the effects of two routes of ampicillin administration. Our results suggest that fecal bla_TEM genes quantification provides a sensitive tool to evaluate the impact of ampicillin administration on the selection of ampicillin resistance in the digestive microflora and its dissemination in the environment.

This article has been cited by other articles:

• Alexander, T. W., Reuter, T., Sharma, R., Yanke, L. J., Topp, E., McAllister, T. A. (2009). Longitudinal Characterization of Resistant Escherichia coli in Fecal Deposits from Cattle Fed Subtherapeutic Levels of Antimicrobials. Appl. Environ. Microbiol. 75: 7125-7134 [Abstract] [Full Text]  
• Bibbal, D., Dupouy, V., Prere, M. F., Toutain, P. L., Bousquet-Melou, A. (2009). Relatedness of Escherichia coli Strains with Different Susceptibility Phenotypes Isolated from Swine Feces during Ampicillin Treatment. Appl. Environ. Microbiol. 75: 2999-3006 [Abstract] [Full Text]