title: Colonization dynamics of ampicillin-resistant Escherichia coli in the infantile colonic microbiota.
abstract: OBJECTIVE
  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 beta-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 bla(TEM) (84%) or bla(SHV) 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 bla(SHV). In 31 of 32 cases, colonization by ampicillin-resistant strains occurred in infants not previously treated with beta-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 beta-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 beta-lactamase genes, therefore, may only slowly be eliminated from the commensal E. coli strain pool.
authors.affiliation: Department of Clinical Bacteriology and Virology, University of Gothenburg, Gothenburg, Sweden. nahid.karami@microbio.gu.se
authors.forename: Nahid
authors.initials: N
authors.lastname: Karami
authors.forename: Charles
authors.initials: C
authors.lastname: Hannoun
authors.forename: Ingegerd
authors.initials: I
authors.lastname: Adlerberth
authors.forename: Agnes E
authors.initials: AE
authors.lastname: Wold
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000668:Ampicillin Resistance; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D003106:Colon / Q000382:microbiology*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics; D005243:Feces / Q000382:microbiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008826:Microbial Sensitivity Tests; D037521:Virulence Factors / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D037521:Virulence Factors; D000667:Ampicillin; D001618:beta-Lactamases