Feed Lot Magazine Online, The Real Antibiotics Issue, Part IV

In previous installments we have discussed how there is a mistaken belief on the part of the medical community that low level antibiotic use is the cause of resistant bacteria. The reality is that high level use genetically selects for resistant bacteria.

High level use, also known as therapeutic, is the type of use required in medical situations. While the medical community has no alternative to high level use,

the frequency and advisability of antibiotic use is an option. Unfortunately, physicians are well known to overprescribe antibiotics. Most commonly, antibiotics are prescribed for virus infections (such as the common cold) which are not susceptible to antibiotics.

According to the Center for Disease Control (CDC), each year there are over 50 million unnecessary prescriptions. Table I illustrates the number and type of unnecessary prescriptions. Table II illustrates how resistance is decreased when therapeutic use of an antibiotic is curtailed.

Salmonella. Even with this evidence, critics maintain that the source for Salmonella infections is food, and since we use antibiotics in food animals, we are responsible for the emergence of resistant strains of Salmonella. That is a serious charge.

The problem is that a lot of people are confusing Salmonella with the Staph and Streptococcus "super bugs." The fact is that the "super" bacteria that have the medical community most concerned, have nothing to do with Salmonella or other bacteria associated with food animals.

The reality is that Salmonella from food animals are not exposed to human antibiotics and have never been found in the animal to have resistance to multiple human antibiotics. Commonly Salmonella are found resistant to various forms of penicillin, as penicillin and derivative products are commonly used in dairy cattle. Likewise, Salmonella are commonly found resistant to tetracycline, which are often used in animals. But "super" Salmonella have never been found in the animal. That is, unlike the "super" Staph and Strep bacteria frequently encountered in hospitals, Salmonella in animals do not show resistance to a broad battery of human antibiotics. Frequently Salmonella infections in humans are found to have resistance to human antibiotics, but in almost all cases the resistance was derived from antibiotics taken by the patient. The most common scenario has been that the patient was taking antibiotics for some other reason, when they acquired the Salmonella infection.

Illegal Use. This does not mean there have not been problems, because there have. In late 1970 and then again in the 1980's there were several cases in which Salmonella infections were encountered which were resistant to chloramphenicol, the preferred drug for treatment of severe cases of salmonella in humans. Chloramphenicol is a prohibited drug for use in food animals, but as it turned out veterinarians had illegally supplied dairy farms with chloramphenicol for treating their calves.

While this is a black mark against animal agriculture, it is important to realize it had nothing to do with the legal use of low level antibiotics. It was therapeutic use of a prohibited drug.

Banning the use of low level antibiotics would not have impacted this situation in any way. Likewise, limiting all drug use in animals to prescription only would also have had no effect since chloramphenicol was already a prescription drug. Indeed as we discussed last time, this has been the approach in Great Britain (low level use is banned and all therapeutic use is by prescription), yet Britain has more cases of resistant Salmonella than the U.S. or Canada.

It is also important to realize these isolated incidences were the only scenario in which drug use in animals has ever impacted human health. Salmonella readily develop resistance, and will develop resistance to drugs administered to animals. But with this one exception, Salmonella resistant to human drugs (other than penicillin) have never been encountered in the animals.

Bottom line. While Salmonella and other enteric bacteria transmitted by animal products will readily develop resistance to antibiotics, organisms with multiple resistances to human antibiotics have not been encountered in the animal. Salmonella should not be confused with the "super" bugs. The ultimate reality is that the "super" resistant staph and streptococcus organisms are created due to overuse of antibiotics in humans.

In the next issue, we will discuss why there is so much overuse in humans.