Tigecycline is an antibiotic of last resort - one that is used when all others have failed. Now a team of Spanish investigators has identified the first documented example of tigecycline-resistant bacteria in hospital that are adapted to living on companion animals - in this case, dogs. The research is published in Antimicrobial Agents and Chemotherapy, a journal of the American Society for Microbiology.

This finding raises the strong possibility that tigecycline-resistant bacteria have been, and are being introduced repeatedly into hospitals, said Bruno Gonzalez-Zorn, DVM, PhD, professor of microbiology at the Veterinary School and Health Surveillance Center, VISAVET, Complutense University, Madrid, Spain. "This is extremely important for public health," he said.

The bacteria harboring the resistance are Klebsiella pneumoniae, which frequently are associated with hospital-acquired pneumonia, bloodstream infections, wound and surgical site infections, and meningitis. These particular K. pneumoniae turned out to belong to two clones that have been disseminated to hospitals worldwide.

The researchers were motivated to investigate antimicrobial resistance in companion animals as resistance is the most important threat to public health, according to the United Nations and the World Health Organization, and because companion animals have long been a neglected link in research into antimicrobial resistance. In the study, they analyzed bacteria that had been isolated from dog patients at the Veterinary Hospital of the Complutense University.

"These are human pathogens, which have become able to colonize dogs, and retain resistance to tigecycline," said Gonzalez-Zorn. "They probably became resistant to tigecycline in the hospital environment, as these animals had not been treated with tigecycline."

Initially, the investigators tested resistance in the bacteria to veterinary antibiotics. Only later did they test resistance to antibiotics used against human pathogens. "And there, we realized the astonishing result: the bacteria were resistant to tigecyline, the last resort antibiotic for humans that is used exclusively in hospitals."

The findings "show the adaptation of human [pathogens] to animals, increasing the spread of resistance mechanisms against one of the last therapeutic options for complicated infections in humans," the investigators write.

That raises the possibility that dog-owners and others in close contact with dogs may be infected with hospital pathogens that are resistant to last resort antibiotics, said Gonzalez-Zorn. The investigators are conducting whole genome sequencing in an effort to determine the hospital where these resistant K. pneumoniae originated.

"Treatment of pet animals with antibiotics should be done with care, and minimized, the same as with humans and food animals."

Article: Klebsiella pneumoniae ST11 and ST147 highly resistant to tigecycline from companion animals, Cristina M. Ovejero, Jose Antonio Escudero, Daniel Thomas-Lopez, Andreas Hoefer, Gabriel Moyano, Natalia Montero, Carmen Martin Espada, and Bruno Gonzalez-Zorn, Antimicrobial Agents and Chemotherapy, doi: 10.1128/AAC.02640-16, published online 10 April 2017.