Enzyme can switch off livestock drugs

Scientists have found that an antimicrobial resistance gene in bacteria collected at a western Canadian feedlot creates an enzyme that can deactivate drugs used to treat diseases in cattle and other livestock.

The EstT enzyme can affect macrolides antibiotic drugs such as tylosin, also sold as Tylan, which is a common additive in feed to help prevent liver abscesses in cattle in feedlots, said Tony Ruzzini, assistant professor at the Western College of Veterinary Medicine at the University of Saskatchewan.

The enzyme can also affect tilmicosin, or Micotil, which helps treat bovine respiratory disease in beef and dairy cattle, he said. The illness, commonly known as shipping fever, is a major cause of mortality in feedlots.

EstT can also affect tildipirosin, also sold as Zuprevo, which is another way to treat bovine respiratory disease, said Ruzzini. These three specific drugs are not used to treat humans, he said.