The present invention relates to compositions and methods using an isolated chimeric molecule, wherein the isolated chimeric molecule comprises an antibody, one or more albumin motifs, optional peptide linkers, and two or more antibiotics or cytotoxic drug molecules conjugated to the unpaired cysteine residues, optionally through linkers. In one embodiment, each of the said albumin motifs in the isolated chimeric molecule contains 2 or more unpaired cysteine residues. In another embodiment, the said antibody in the isolated chimeric molecule targets antigens on cancer cells or drug-resistant bacteria. In another embodiment, the cancer cells have upregulated macropinocytosis. In another embodiment, the cancer cells contain one or more mutations in their RAS family genes. The compositions of the invention are used to treat drug-resistant bacterial infections and cancers, preferably the ones with upregulated macropinocytosis, and the ones containing one or more mutations in their RAS family genes.
