Lack of effect of Lactobacillus on gastrointestinal bacterial colonization in premature infants.

Studies were carried out on premature infants in the neonatal intensive care unit to determine the effect of feeding of lactobacilli on colonization of the gastrointestinal tract by antibiotic-resistant gram-negative enteric organisms. Thirty premature infants were matched by birth weight and gestational age, randomized and fed double blind either lactobacilli-containing formula or non-lactobacilli-containing formula within 72 hours of delivery. The two study groups were screened weekly by culture for stool lactobacilli, for gram-negative bacteria and for antibiotic resistance of these bacteria. Lactobacilli were cultured from the stools of 13 of 15 patients receiving lactobacilli and from 3 of 15 patients not receiving lactobacilli (P less than 0.001). Gram-negative enteric organisms were isolated during 40 of the 86 weeks (47%) of hospitalization for patients receiving lactobacilli and during 28 of 57 weeks (49%) for patients not receiving lactobacilli. There was no significant difference between the study groups in the number of resistant organisms or in the proportion of resistant organisms per gram-negative enteric isolates (4 of 40 vs. 0 of 28). These results suggest that facultative gram-negative enteric bacterial colonization, with either total or aminoglycoside-resistant strains, is not decreased by oral feedings of Lactobacillus acidophilus in premature infants.