Influence of antibiotic therapy on faecal carriage of P-fimbriated Escherichia coli and other gram-negative bacteria in neonates.

The influence of previous antibiotic therapy on the aerobic faecal flora, including P-fimbriated Escherichia coli, was studied in 953 neonates at discharge from 22 neonatal wards in Sweden. Antibiotics, mainly ampicillin (with or without gentamicin) or cefuroxime, had been received by 37% of the infants. Treatment with ampicillin (with or without gentamicin) increased Klebsiella/Enterobacter and reduced Esch. coli colonization. Cephalosporin therapy (71% cefuroxime) reduced the frequency of colonization with both Esch. coli and Klebsiella/Enterobacter spp. but doubled the isolation rate of other Gram-negative bacteria (Citrobacter, Pseudomonas, Proteus and Acinetobacter spp.) and tripled the incidence of specimens yielding no aerobic Gram-negative growth. Gentamicin showed no significant ecological impact. The selection of Klebsiella/Enterobacter and P-negative Esch. coli strains by ampicillin was correlated with their resistance to this agent, while the association between P-fimbriated Esch. coli and cefuroxime therapy was not related to cefuroxime resistance.