The question of whether or not antibiotic use in livestock leads to antibiotic resistant infections in humans led to a dust-up that has lasted for decades. Until this year the issue was clouded by a lack of substantiated proof either way. But now researchers at the University of Cambridge have used whole genome sequencing (WGS) to investigate the matter and the answer they found was yes, the bacteria can be transmitted between animal and man.
It’s not that anyone questioned that antibiotic resistant bacteria developed on farms, for that has been known for ages. Instead the debate centered on whether the evolved bacteria could and did cross from farm animals to humans.
Until now, tracking the bacteria path has been precarious at best since it came loaded with too many variables to come to a definite conclusion.
At stake are human lives on the one end and on the other the agricultural industry’s need to provide more food, faster and safer. In other words, reducing antibiotic use in livestock could potentially curb the rise of antibiotic resistant disease in humans. But, reducing antibiotic use in livestock could diminish the food supply, or render it unsafe, at a time when the need for food is growing exponentially.
The answer to the question then, no matter which way it went, was bound to essentially be bad news.
Nonetheless, an answer is needed before anyone can set about the business of finding an actual solution.
Enter the Cambridge study, “Whole genome sequencing identifies zoonotic transmission of MRSA isolates with the novel mecA homologue mecC” which was able to examine a clearer bacteria path from infected animals to infestation in humans and verify that path via whole genome sequencing.
The researchers found two infected women in Denmark where human cases of the antibiotic resistant staph known as MRSA are exceedingly rare. Both women owned livestock. The first owned two horses and two cows; the other owned a small flock of sheep. The researchers found that one cow and three of the sheep carried the strain. Whole genome sequencing directly tied the infected animals to their respective owners.
It wasn’t just the fact that the isolates between each farmer and animal were functionally identical that convinced the researchers to reach the conclusion that the disease had indeed spread from animal to human. The ultimate deciding factor came from the third sheep’s strain that varied slightly both from the strain in the other sheep and from that in the woman thus showing the disease had changed in order to make the species leap.
Now, arguments can be made that the study’s findings may be flawed in that the MRSA strain found in the study is not the standard form and therefore may not apply to the transmission of the standard or other strains; there were only two cases studied so the findings may not hold true across a larger sampling; and, that the two women did not dose their animals with antibiotics and yet the disease evolved and transmitted to the women anyway.
Nonetheless, whole gene sequencing did provide the means to accurately and directly track the bacteria path. And that in itself is nothing short of miraculous.
For more information on how antibiotic resistant bacteria comes into existence, take a look at this short video…