The sequences of all replicons of a bacterial isolate are linked to a common entry in the taxonomy database, and to a common entry in the biosample database. The genome of a bacterial cell may comprise several replicons, but the number of plasmids may vary within a species. Plasmids usually encode non-essential genes, and they can be acquired or lost.
If the accession of a sequence starts with AP, CP or BA, it is a complete replicon and it always has an associated entry in the taxonomy database. The entry in the taxonomy database refers to the bacterial isolate which has been sequenced, it is a sub-species entry. Example: pathogenic "Escherichia coli O157:H7 str. Sakai" having one chromosome and two plasmids
All newer full bacterial sequences are also linked a an associated entry in the biosample database. You can then use the biosample ID to find all replicons belonging to an isolate. Example: "Staphylococcus warneri SG" has one chromosome and 8 plasmids: