Background: To study the factors implicated in the infectious process (host, microorganism and antibiotic) of a newborn early sepsis by S. agalactiae that suffered a reactivation at day five from discharge.
Methods: Description of two episodes of newborn sepsis by S. agalactiae corresponding to the same patient and microbiologic study of the isolated strain: typing by "genomic macrorestriction" and antibiotic tolerance by "timed killing curves".
Results: It was demonstrated that both strains of S. agalactiae type la/c belonged to the same clone as well as the tolerance to ampicillin of the strain.
Discussion: This sort of infections processes in the newborn are very serious and there is possibility of relapse. Thus, it is important to study the ethiologic agent and its relationship with antibiotics, in order to stablish the best treatment regimes, avoiding the possibility of relapses as the case we have described.