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JAC Advance Access published online on June 25, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn263
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Original research

Colonization dynamics of ampicillin-resistant Escherichia coli in the infantile colonic microbiota

Nahid Karami*, Charles Hannoun, Ingegerd Adlerberth and Agnes E. Wold

Department of Clinical Bacteriology and Virology, University of Gothenburg, Gothenburg, Sweden

Received 3 March 2008; returned 16 April 2008; revised 28 May 2008; accepted 1 June 2008

* Corresponding author. Tel: +46-31-3424636; Fax: +46-31-3424729; E-mail: nahid.karami{at}microbio.gu.se

Objectives: To compare the colonization dynamics of ampicillin-resistant and ampicillin-susceptible Escherichia coli strains in the infantile intestinal microbiota.

Methods: We followed 128 infants over the first year of life with regular quantitative faecal cultures and recordings of antibiotic treatment. E. coli strains were quantified, and their resistance pattern and carriage of β-lactamase genes (TEM, SHV and OXA), phylogenetic group (A, B1, B2 or D), virulence gene profile (fimA, papC, sfaD/E, kfiC neuB, hlyA and iutA) and time of persistence in the microbiota were determined.

Results: Twelve percent (n = 32) of the E. coli strains were resistant to ampicillin, as they carried the blaTEM (84%) or blaSHV genes. Ampicillin-resistant strains belonged mostly to phylogenetic group D and carried pap genes (P = 0.023) significantly more often than ampicillin-susceptible strains due to a strong association between carriage of pap and blaSHV. In 31 of 32 cases, colonization by ampicillin-resistant strains occurred in infants not previously treated with β-lactam antibiotics. Ampicillin-resistant strains were equally capable as susceptible ones of persisting in the intestinal microbiota and did not have lower faecal population counts. Genes encoding β-lactamases were in most cases retained during the entire colonization period.

Conclusions: The results suggest that ampicillin-resistant E. coli strains are not hampered in their colonizing capacity, and β-lactamase genes, therefore, may only slowly be eliminated from the commensal E. coli strain pool.

Key Words: E. coli , β-lactamases , virulence factors , persistence , phylogeny


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