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Single Nucleotide Mutation Found to Alter Staph aureus ST21 Tropism from Humans to Rabbits; Surprising Result Dictates Paradigm Shift in Thinking about Transmission of Bacterial Diseases between Humans and Animals

A new study suggests that bacteria may be able to jump between host species far more easily than was previously thought. Researchers have discovered that a single genetic mutation in a strain of bacteria infectious to humans enables it to jump species to also become infectious to rabbits. The discovery has major implications for how we assess the risk of bacterial diseases that can pass between humans and animals. It is well known that relatively few mutations are required to support the transmission of viruses, such as influenza, from one species to another. Until now, it was thought that the process was likely to be far more complicated for bacteria. The new study was published online on February 16, 2015 in Nature Genetics. The title of the article was “A Single Natural Nucleotide Mutation Alters Bacterial Pathogen Host Tropism.” Scientists at the Universities of CEU Cardenal Herrera (Spain), and of Glasgow (UK), and of Edinburgh (UK) studied a strain of bacteria called Staphylococcus aureus ST121, which is responsible for widespread epidemics of disease in the global rabbit farming industry. The team looked at the genetic make-up of S. aureus ST121 to work out where the strain originated and the changes that occurred that enabled it to infect rabbits. The scientists found that S. aureus ST121 most likely evolved through a host jump from humans to rabbits approximately 40 years ago, with a genetic mutation at a single site in the bacterial DNA code being the cause for this.

This discovery transforms our understanding of the minimal genetic changes that are required for bacteria to infect different species. S. aureus ST121 is found in the respiratory tract and on the skin of some people. While it is usually harmless, the bacteria can cause a variety of conditions from minor skin infections to meningitis and sepsis. In rabbits, the bacteria can cause serious skin infections.

Professors David Viana, of the CEU-UCH Veterinary Faculty, and Dr. Jose Penades, of the Institute of Infection, Immunity, and Inflammation at the University of Glasgow, who, together with Professor Ross Fitzgerald from the University of Edinburgh’s Roslin Institute, co-led the study, said: “The ability for pathogens to switch host species and lead to an epidemic in a new host population is of major concern to veterinary and public health professionals. Our results represent a paradigm shift in understanding of the minimal adaptions required for a bacterium to overcome species barriers and establish in new host populations.”

Professor Fitzgerald added: “Domestication of animals, industrialization of agriculture, and globalization have provided new opportunities for the transmission of bacteria between humans and animals. This latest research has important public and veterinary health implications that will require a re-examination of the future threat posed by bacterial host switching events.”

The study was funded by the University of Glasgow, the Biotechnology and Biological Sciences Research Council, and the Medical Research Council.

[Press release] [Nature Genetics abstract]

http://upload.wikimedia.org/wikipedia/commons/b/bd/Scanning_electron_micrograph_of_Methicillin-resistant_Staphylococcus_aureus_(MRSA)_and_a_dead_Human_neutrophil_-_NIAID.jpg