The occurrence of antimicrobial resistance and class 1 integrons among commensal Escherichia coli isolates from infants and elderly persons.

Background: The aim of our study was to compare the presence of the intI1 gene and its associations with the antibiotic resistance of commensal Escherichia coli strains in children with/without previous antibiotic treatments and elderly hospitalized/healthy individuals.

Methods: One-hundred-and-fifteen intestinal E. coli strains were analyzed: 30 strains from 10 antibiotic-naive infants; 27 from 9 antibiotic-treated outpatient infants; 30 from 9 healthy elderly volunteers; and 28 from 9 hospitalized elderly patients. The MIC values of ampicillin, cefuroxime, cefotaxime, gentamicin, ciprofloxacin, and sulfamethoxazole were measured by E-test and IntI1 was detected by PCR.

Results: Out of the 115 strains, 56 (49%) carried class 1 integron genes. Comparing persons without medical interventions, we found in antibiotic-naive children a significantly higher frequency of integron-bearing strains and MIC values than in healthy elderly persons (53% versus 17%; p < 0.01). Evaluating medical interventions, we found a higher resistance and frequency of integrons in strains from hospitalized elderly persons compared with non-hospitalized ones. Children treated with antibiotics had strains with higher MIC values (when compared with antibiotic-naive ones), but the integron-bearing in strains was similar. In most cases, the differences in resistance between the groups (integron-positive and negative strains separately) were higher than the differences between integron-positive and negative strains within the groups.

Conclusion: The prevalence of integrons in commensal E. coli strains in persons without previous medical intervention depended on age. The resistance of integron-carrying and non-carrying strains is more dependent on influencing factors (hospitalization and antibiotic administration) in particular groups than merely the presence or absence of integrons.