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Tetracycline resistance in Escherichia coli and persistence in the infantile colonic microbiota.

Journal article
Authors Nahid Karami
Forough Nowrouzian
Ingegerd Adlerberth
Agnes E Wold
Published in Antimicrobial agents and chemotherapy
Volume 50
Issue 1
Pages 156-61
ISSN 0066-4804
Publication year 2006
Published at Institute of Biomedicine, Department of Infectious Medicine
Pages 156-61
Language en
Keywords Colon, microbiology, Drug Resistance, Microbial, Escherichia coli, drug effects, Escherichia coli Infections, drug therapy, microbiology, Feces, microbiology, Humans, Infant, Microbial Sensitivity Tests, Tetracycline, pharmacology, therapeutic use, Tetracycline Resistance
Subject categories Microbiology in the medical area


The ecological impact of antibiotic resistance in the absence of selective pressure has been poorly studied. We assessed the carriage of tetracycline resistance genes, persistence in the microbiota, fecal population counts and virulence factor genes in 309 commensal, intestinal Escherichia coli strains obtained from 128 Swedish infants followed during the first year of life with regular quantitative fecal cultures. No infant was given tetracycline, but 25% received other antibiotics. Tetracycline resistance was identified in 12% of strains, all of which carried either tet(A) (49%) or tet(B) (51%) genes. Resistance to other antibiotics occurred in 50% of tet(A)-positive strains, 42% of tet(B)-positive strains and 13% of tetracycline-sensitive strains. However, colonization with tetracycline-resistant strains was unrelated to treatment with antibiotics. Strains that were tet(B)- or tet(A)-positive carried the genes for P fimbriae and aerobactin, respectively, more often than susceptible strains. Tetracycline-resistant and -susceptible strains were equally likely to persist among the intestinal microbiota for > or = 3 weeks and had similar population numbers. However, when a resistant strain and a susceptible strain colonized a child simultaneously, the resistant variety showed lower counts (P = 0.03). In cases of long-term colonization by initially tetracycline-resistant E. coli strains, loss of tet genes occurred in 3 of 13 cases with variable effects on population counts. The results indicate that there is limited pressure against the carriage of tet genes in the infantile gut microbiota even in the absence of antibiotics. Resistant strains may possess colonization factors that balance the cost of producing resistance elements.

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