RESUMEN
We studied the intestinal flora of 23 newborns, whose meconium had yielded a pure culture of Pseudomonas aeruginosa on blood agar medium. Twelve infants had a single serotype of P. aeruginosa in their meconium, 10 had a second serotype and the last infant was carrying three distinct ones. The maximum levels of P. aeruginosa observed during the first week of life were variable among the infants: 1 x 10(3) to 1 x 10(10) CFU/g of stools. The levels diminished progressively afterwards, and after 1 year of age only 1 of the 13 infants examined remained a carrier of P. aeruginosa. In 11 infants a second or a third serotype occurred during the course of the study. The serotypes that appeared secondarily always disappeared before the initial ones. Antibiotics: ampicillin + gentamicin or cefotaxime + netilmicin and colistin which were given to 8 infants had no clear effect on P. aeruginosa levels. Four infants had delayed colonization by Escherichia coli of greater than or equal to 10 days. All 4 had high levels of P. aeruginosa: 1 x 10(7) to 1 x 10(10) CFU/g stool, and antibiotic therapy, rendering it impossible to assess which was the cause of this delay. This colonization by P. aeruginosa did not lead to any clinical trouble.