Emerging Resistance from Antibiotics in Animal Feed

Many scientists are concerned about potential problems from the relationship between the use of the agents in food-producing animals and the emergence of Salmonella serotypes with reduced suspecitibility to flouroquinolones in humans. Since its introduction into poultry, there has been a significant increase in flouroquinolone resistant Campylobacter Jejuni isolated in live poultry, poultry meat, and humans in the U.S., U.K. and Holland. Surveillance for antimicrobial resistance is being expanded and an FDA study will soon be launched of resistant pathogens found in retail foods. One of the big concerns raised is that reducing antimicrobial use in food animals will cause production costs to rise considerably.

“The experience of the European Union with respect to withdrawal of approval for use of sub therapeutic antibiotics needs to be closely scrutinized,” said Randy Huffman, Ph.D., vice president of Scientific Affairs at the American Meat Institute Foundation.

“When meat and poultry are produced under federal inspection and prepared properly at home, these products are very safe — among the safest meat products in the world.”

Currently, he says, the scientific community believes that bacteria that have genetic traits that allow resistance to antibiotics are not any more hardy to the normal handling and cooking practices that U.S. manufacturers and consumers use every day to ensure food is safe to eat.

“There is no evidence to conclude that bacteria become more resistant to normal cooking temperatures just because they have developed genetic resistance to a certain class of antibiotics,” Huffman says. “Proper cooking will ensure safety all the time.”

In July 2005, the FDA announced it would no longer allow the distribution of enrofloxacin for the purpose of treating bacterial infections in poultry. Enrofloxacin — a fluoroquinolone — is marketed under the name Baytril by the Bayer Corp. Scientific data collected by the FDA indicated that use of the drug encouraged resistance to Campylobacter, a foodborne illness usually harbored in the intestines of poultry. Baytril is a close cousin to the human antimicrobial Cipro. So, the question begs — are poultry products a more risky food in terms of harboring bacteria? Does any one animal food pose more of a danger than another?

“This is an important question but difficult to answer,” said Dr. Tom Chiller, chief medical epidemiologist for the Foodborne Diseases branch of the Centers for Disease Control and Prevention (CDC). “We are currently working on trying to understand how to estimate and attribute foodborne illness to specific sources. If we look at the retail meat surveillance done by (FDA-CVM), we see that poultry meat purchased from grocery’s have a much higher prevalence of Salmonella and Campylobacter than do ground beef and pork chops, but having the higher prevalence does not mean that there are higher infection rates. This kind of data is being put together by an attribution group and hopefully there will be some estimates coming out next year.”

How Resistance Traits Spread

Many disease-causing organisms have the ability to defend themselves. There are two basic events that occur for resistance to develop and cause a problem; first there is the emergence of the resistance and then the dissemination. Through the process of mutation or gene transfer, bacteria can become resistant to the effects of antibiotics, allowing them to thrive even when a person or an animal takes an antibiotic. For example, frequently exposing a person or an animal to an antibiotic will kill susceptible bacteria in the body, but a small mutation in the genome of other bacteria may allow them to become resistant or escape the effects of the antibiotic. If this happens, antibiotic-resistant bacteria can soon outnumber the antibiotic-susceptible bacteria. This increases the chances for a person or an animal to develop an infection caused by a resistant organism, rather than an antibiotic-susceptible one. Since bacteria between are frequently transmitted between people, between animals, and in some cases, between animals and people, people and animals who have not taken antibiotics may still become infected with antibiotic-resistant bacteria. Depending upon the types of resistance that develop, it may be difficult to treat an antibiotic-resistant infection, requiring additional antibiotics and more expensive treatments.