Distribution and diversity of a cadmium resistance (cadA) determinant and occurrence of IS257 insertion sequences in Staphylococcal bacteria isolated from a contaminated estuary (Seine, France).

Water and sediments of the Seine estuary are contaminated by chemicals, especially cadmium, which favors survival and growth of cadmium-resistant bacteria. We investigated the diversity of the cadA gene, which encodes a Cd(2+)/ATPase protein transporter, in the microbial community of the Seine estuary. The cadA gene first isolated from S. aureus (pI258) was prevalent, with a conservation better than 98% identity, despite its presence in host bacteria of diverse species and genera. We report for the first time, eleven distinct Staphylococcus species, and also bacteria belonging to the Micrococcus and Halobacillus genera carrying the cadA gene. This cadA determinant was mostly plasmid-borne in the Staphylococcus genus, and IS257 sequences, which are known to participate in antibiotic resistance gene dissemination in S. aureus, were found to be located near to the cadA gene in 16/31 cadmium-resistant Staphylococcus strains and one Micrococcus strain. This suggests that IS257 has also contributed to the dissemination of the cadA resistance gene among staphylococci. These findings also emphasize on the existence of Staphylococcal bacteria in contaminated natural niches outside hospital environments.