Have you been to the grocery store recently and chosen that chicken cut that is not treated with antibiotics? Or did you choose one that was treated with antibiotic, thinking all bacteria in it would be dead?

According to recent research (1), farms may be more effective sources of transmission of antibiotic-resistant bacteria to the community than hospitals. Fresh poultry from animals not treated with antibiotics will probably pose a smaller risk to your health. If you catch any disease from it, antibiotics will really work for you if you need them.

Any bacteria harmful to humans that are left in the antibiotic-treated meat after the antibiotic kills the others will certainly be a significant hazard, if not to you, to the population as a whole. The super-bugs caught from these meats will be hard to kill; for, once they have been exposed to antibiotics, they become resistant to them after some time.

Fighting an infection caused by these bacteria will be much more difficult than fighting bacteria that are not resistant. Like in the recent cases of MRSA, many people either do not get rid of them easily, or continue having the infection for some time in spite of the treatment.

Antibiotics and antibiotic-resistant bacteria are in the air and soil around farms, in surface and ground water, among wild animal populations, as well as on retail meat and poultry. They end up in your kitchen, and contaminate other foods by unsafe handling practices; and if they are able to override the gastric barriers your body has against them, they settle in your gut.

They might live there for a long time without any signs of infection, but ready to be transmitted to other carriers. One or two cases of this kind are enough if the transmission rate is high; that is, if the bacteria are highly contagious. Without appropriate control measures, the harm done by these resistant bacteria starts to spread throughout the community, and affect people that are more susceptible than the carriers.

Some variants of antibiotic-resistant bacteria transmitted in this way might evolve then that never were found among humans. If these new variants are harmful to humans and highly and rapidly transmissible within the human population, the agricultural antibiotic impact must be carefully assessed.

The number of people that carry antibiotic resistant bacteria due to contaminated meals is approximately the same as the one generated by a hospital. This happens because, although we have much less chance of getting antibiotic resistant bacteria in each individual meal than in a hospital, a large number of people are exposed to a small risk in contrast with the small number exposed to a high risk (when we go to the hospital). People eat at least three times every day, so we have more than a thousand chances a year to be exposed to a small risk of infection carried by contaminated food. But the average healthy person spends just some days in a year at the hospital, where the risk of getting resistant bacteria is higher.

A large-scale natural experiment conducted in the US and several European countries showed that resistant bacteria evolved more frequently in the European Union before the use of antibiotics in agriculture was banned.

Many European countries approved avoparcin for animal growth promotion in the 1970s, but the US did not. In the early 1980s, vancomycin started to be used in the U.S. hospitals due to an increase in resistance of Staphylococcus aureus (the famous MRSA, which is attacking our school kids nowadays) to other antibiotics. Vancomycin is still being used in hospitals to fight MRSA.

Some strains of vancomycin-resistant enterococci appeared in the late 1980s and early 1990s, spreading through U.S. health-care systems. In Europe, vancomycin was less used, for most enterococci were sensitive to other antibiotics. The resistant bacteria appeared there too, but in a less severe way than in the U.S. That was the phase in which the antibiotic in the poultry and meats was still effective against the bacteria.

During the late 1990s, though, the resistant enterococci were more frequent in the community, including in people who had not been previously in a hospital. That showed that the bacteria in the food were starting to get resistant to the agricultural antibiotics.

The result was that the European community pool of resistant bacteria, generated by the use of antibiotics in hospitals and agriculture, was apparently much larger than in the U.S., where the resistance was generated only by use of vancomycin in hospitals. After EU banned avoparcin, the resistance to bacteria in the community was reduced. That is, the impact of the agricultural antibiotics in European hospitals was larger than the impact of US hospitals on one another.

The European Union banned the use of antibiotics for growth promotion based on the precautionary principle. In this case, it is more scientific to simply ban the product that might be the cause of the resistance, than simply do nothing because there are no precise means to measure the complex interaction between organisms and transmission of resistance in bacteria.

Therefore, since bacteria like the MSRA spread more rapidly in the population when they are found in contaminated food, precautionary measures such as banning agricultural antibiotics are highly effective in controlling the impact of these bacteria in the population.