Abstract
Background: The intestinal tract of the fetus is sterile but after birth is colonized with bacteria from the mother and environment. Multiple factors affect the postnatal colonization of the GI tract. Early exposure of newborn infants to antibiotics may be associated with disturbances in the normal postnatal acquisition of the intestinal flora. Most of the previous studies used classical culture methods that only identify a limited number of bacterial species. Recently, the use of molecular techniques has greatly improved the study of GI ecology.
Objectives: This is an ongoing descriptive study designed to examine the effect of antibiotic exposure on the postnatal intestinal bacterial colonization of term newborns, by using comparative analysis of clone libraries of 16S rRNA genes.
Methods: We plan to enroll a total of 20 infants GA>37, divided in 2 groups: antibiotic-treated (7 day course) and non-treated (control) infants. Stool samples are collected from each infant on day 3-5, day 7-10 and day 20-30 of life. DNA is amplified using universal bacterial primers. PCR products are cloned and for each sample, a library of about 96 clones is obtained.
Results: To date, we have collected 43 stool samples from 15 infants (8 study patients and 7 controls). Clone libraries from 19 samples are available so far. Our preliminary results show that Lactobacillus, Enterobacteria or Enterococcus dominate early colonization of control infants (in one infant 63% of the clones were Lactobacillus, in 2 infants 75% and 81% of the clones were Klebsiella and Escherichia, respectively, and in 2, Enterococcus clones were isolated in 56% and 95% respectively). By day 7-10 intestinal flora was more diverse and included Enterobacteria, Clostridia, Steptococcus and Enterococcus (with no one dominating). By day 20-30 there was again an increased predominance of Enterobacteria but other species were also present. Infants exposed to antibiotics (2 analyzed to date) had a less diverse intestinal flora on the initial sample, dominated by either Lactobacillus or Bacteroides. At 7-10 days, the flora was dominated by Enterobacteria (90%). By one month of age, the number of species identified increased similarly to infants that were not exposed to antibiotics.
Conclusion: Our preliminary observations suggest that early exposure to antibiotics may be associated with decreased diversity of intestinal bacterial colonization. As known, there is a relative paucity of bacterial species in the initial intestinal colonization of newborns. The number of species decreases further during and after antibiotic treatment. By one month of age the flora is again more diverse. As our sample size increases, we anticipate further clarification of the effect of antibiotic treatment and other perinatal factors in modifying the stool bacterial ecology.
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Turcu, R., Marsh, T., Patterson, M. et al. 46 Effect of Antibiotics on Postnatal Intestinal Colonization in Term Newborns. Pediatr Res 60, 498 (2006). https://doi.org/10.1203/00006450-200610000-00068
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DOI: https://doi.org/10.1203/00006450-200610000-00068