Characterization of lactose-fermenting Salmonella agona strains isolated in a pediatric unit

Eight lactose-fermenting Salmonella Agona strains isolated in a pediatric unit were characterized by classic and molecular methods. The strains were classified as biotype la, corresponding to the most frequent one in Brazil. None of the strains produced colicin. Multiple resistance to antimicrobials was observed among the strains studied. It was demonstrated that the lactose-fermenting character was encoded by a plasmid with spontaneous segregation at a frequency of 1%. This plasmid was transferable by conjugation at a frequency between 4 x 10(-8) and 5 x 10(-10). The Lac(+) plasmid, which molecular weight was approximately 90 MDa, encoded both lactose fermentation and multiple resistance to antimicrobials. Replicon typing showed that this plasmid did not belong to the known types, suggesting the presence of a new replicon type. Classic methods showed that the studied strains had the same characteristics as the clone widely occurring in our area, differing only by lactose-fermenting ability. This conclusion was supported by the results of ribotyping study.