The human insulin gene has been engineered into E. coli to produce large quantities of human insulin. Growth hormone, clotting factors, antibiotics, industrial enzymes and vaccines have all been produced using recombinant DNA and genetic engineering in prokaryotes.Transgenic plants can be produced using Agrobacterium tumefaciens, a bacterium that causes tumours in plants. The desired gene can be placed in the Ti plasmid with marker genes for fluorescence or antibiotic resistance and be used to infect plants. Electrofusion can also be used on plant cells.Transgenic animals are much harder to produce. Growth hormone made by genetically engineered bacteria is injected into cows to increase milk production, but the cows themselves are not transgenic.