New Evidence for Antibiotic-Treated Livestock as a Breeding Ground for Drug-Resistant Bacteria that Spread to Humans

© 2012 Peter Free

 

27 February 2012

 

 

A new study demonstrated that antibiotic resistance can originate (as previously suspected) in the unregulated use of antibiotics in agriculture

 

According to the study:

 

(i) Methicillin-susceptible Staphylococcus aureus appears to have been transmitted from human beings to livestock.

 

(ii) Once in the herd (or flock), these bacteria evolve resistance to methicillin and tetracycline, due to the heavy use of antibiotics in agriculture.

 

(iii) Subsequently, these bacteria are transmitted back to people — where their newly acquired antibiotic-resistance can cause significant problems in medical treatment.

 

Note

 

Methicillin is a penicillin-like antibiotic.  Methicillin-susceptible means that the antibiotic works in controlling bacterial growth.  Methicillin-resistant means that it does not.

 

Staphylococcus aureus can cause a wide range of infections, ranging from mild to serious to deadly.

 

Methicillin-resistant “Staph” is called “MRSA.”  It is resistant to most antibiotics.  If you are seriously sick with MRSA, you can be in significant medical trouble.

 

As a historical note, at the time MRSA was named, methicillin was considered to be the antibiotic of last resort in treating staph infections.  Today, vancomycin has replaced it.  But there is evidence that some bacteria have developed vancomycin-resistance.

 

 

Citation — to the study

 

Lance B. Price, Marc Stegger, Henrik Hasman, Maliha Aziz, Jesper Larsen, Paal Skytt Andersen, Talima Pearson, Andrew E. Waters, Jeffrey T. Foster, James Schupp, John Gillece, Elizabeth Driebe, Cindy M. Liu, Burkhard Springer, Irena Zdovc, Antonio Battisti, Alessia Franco, Jacek Żmudzki, Stefan Schwarz, Patrick Butaye, Eric Jouy, Constanca Pomba, M. Concepción Porrero, Raymond Ruimy, Tara C. Smith, D. Ashley Robinson, J. Scott Weese, Carmen Sofia Arriola, Fangyou Yu, Frederic Laurent, Paul Keim, Robert Skov, and Frank M. Aarestrup, Staphylococcus aureus CC398: Host Adaptation and Emergence of Methicillin Resistance in Livestock, mBio, doi: 10.1128/​mBio.00305-11 (21 February 2012)

 

 

Methods

 

The research team sequenced whole genomes of a wide collection of Staphylococcus aureus samples taken from 19 countries on 4 continents.

 

They grouped these into 89 “core genomes” and identified 4,238 distinguishing differences among them.  Technically, these differences are called “single nucleotide polymorphisms.”

 

Note

 

Polymorphism just means that one of the building blocks of DNA, a nucleotide, is different in a specific DNA strand location from one organism to another.  You probably recall the names of these from high school — adenine, guanine, cytosine, and thymine.

 

Tracking polymorphisms is useful.  DNA differences help to sort the evolutionary lines that different samples of the same (or different) species took to get wherever they are found.

 

In this case, researchers discovered that human-originated Staph aureus suddenly became more genetically diverse, after being transmitted to livestock, and acquired methicillin and tetracycline resistance in the process.

 

 

“So, Pete — if we suspected that agriculture was a reservoir for breeding antibiotic-resistance, why was nothing done to regulate antibiotic use in farming?”

 

Answer — special interests.  And the way our political and regulatory systems are captured by greed, rather than the public interest.

 

From a medical perspective, the routine use of antibiotics for growth promotion under unnaturally crowded livestock conditions in agriculture has been criticized for years.

 

Biological scientists have long known that subjecting bacteria to continually applied antibiotics causes the evolution of antibiotic-resistance.  And it was obvious that agriculture, which accounts for about 70 percent of antibiotic use, was a foreseeable breeding ground for the development of medically troublesome drug-resistance.

 

However, no one, including the politicized (go along to get along) Food and Drug Administration, did anything about it.

 

Money-wise, the creation of antibiotic resistance in people is actually good for the profit-oriented components of the medical establishment.

 

Agriculture certainly doesn’t care, either.  The gains that allegedly accrue from the profligate use of antibiotics in unnaturally crowded livestock conditions outweigh the negatives.

 

Consumers probably don’t care because the industry rationalizes that the widespread use of antibiotics produces cheaper food.

 

In brief, no one in power wants to take on Big Pharma or the farm lobby.

 

And no one in leadership speaks for the people who get sick from this bit of non-regulatory insanity.

 

 

The moral? — The public interest is difficult to achieve, even when it comes to something so basic as preserving health

 

One of the ironies of economic thinking is that economists count the money involved in treating disease as a positive for the Gross Domestic Product.

 

Consequently, money spent on keeping animals unnaturally crowded together and laced with antibiotics — as well as the hospital treatments necessary for people sickened by the drug-resistant bacteria bred there — are both GDP positives.

 

In contrast, regulating the use of antibiotics in agriculture would (arguably) result in a net reduction in the GDP.  Many fewer drugs would be sold.  Fewer human medical treatments would be necessary.  The livestock housing market would take a hit.  And food might become more expensive — or not, depending on how our food preferences evolved.

 

Clearly, if we hold onto our current purely profit-oriented mindsets, this would be a disaster.

 

On the other hand, if the idea that illness is good for the economy doesn’t give us insight into the foolishness of our acculturated perceptions of what counts as profit and what does not, we’re not using our heads (or souls).