Replicon typing characterization of plasmids encoding resistance to gentamicin and apramycin in Escherichia coli and Salmonella typhimurium isolated from human and animal sources in Belgium.

Escherichia coli and salmonella strains with plasmids conferring resistance to gentamicin and apramycin have been isolated with increasing frequency both from cattle and hospital patients in Belgium. The apramycin-gentamicin resistance plasmids were characterized in recipient strains by their profiles and molecular weights using agarose gel electrophoresis, by their antimicrobial resistance patterns and by replicon typing using a series of DNA probes specific for the genes controlling their systems of replication. Overall, most of the plasmids differed in their DNA electrophoretic patterns. Seventeen different antimicrobial resistance profiles were observed, and there were six different types of replicons. However, two replication genes predominated and had a preferential distribution in different bacterial species. The rep FIC.a plus rep Q multireplicon was found mainly in plasmids recovered from gentamicin- and apramycin-resistant E. coli while replicon of the type rep FIC.b largely prevailed in S. typhimurium. Identical replication genes were found in most animal and human strains, hence suggesting a high homology between apramycin-gentamicin plasmids in these communities. Finally, our results indicate that the rapid spread of apramycin-gentamicin-resistance in several species of Enterobacteriaceae isolated from animals and from humans in Belgium is not due to a single plasmid, but rather that the gene encoding AAC(3)-IV is carried by various replicons.