Just mention antibiotic resistance these days and you likely will spark a heated debate. Many groups voice their opinions on the subject — some based on little more than emotion, some based on fact.
Methicillin-resistant Staphylococcus aureus, for example, recently made headlines. The problem may stem from overuse and abuse of the antibiotic among the human population; however, some are pointing an accusing finger at the pork industry. Before jumping to conclusions, it’s important to let science propose a course of action based on fact, not speculation.
The National Antimicrobial Resistance Monitoring System defines antibiotic resistance as bacteria’s ability to resist attack from an antibiotic. Bacteria can do this several ways. For example, some bacteria can rapidly inactivate the antibiotic before it harms them. Other bacteria can alter their physical structure and dodge the assault by removing the antibiotic’s target. (See sidebar.)
Antibiotic resistance is a natural phenomenon. An evolutionary view suggests that bacteria have defended themselves in ingenious ways for billions of years and will continue to do so. It’s no coincidence that antibiotic resistance was recognized relatively soon after the discovery of antibiotics.
On the human side, for antibiotics to retain their effectiveness both doctors and patients must use them responsibly. Doctors who prescribe antibiotics for illnesses not caused by bacteria may contribute to antibiotic resistance. Likewise, patients who don’t complete the full dosing regimen are likely contributing as well.
But whatever challenge they face, whether it comes in the form of heat, cold, disinfectants or antibiotics, a few bacteria usually survive and pass on the ability to adapt to the new condition or environment.
Science reveals secrets
Bacteria aren’t the only ones working overtime; scientists are now able to better understand these minute organisms. Today’s technology allows them to examine and track the genetic material that contributes to antibiotic resistance.
One such study by University of Illinois researchers found that antibiotic-resistance genes sometimes leak from hog waste lagoons into groundwater. The researchers extracted bacterial DNA from lagoons and groundwater wells at two study sites during a three-year period to examine diversity and abundance of tetracycline-resistant genes.
“This is the first study to take a broad sample of tetracycline-resistant genes in a landscape dominated by hog farming,” says R.I. Mackie, the lead researcher. The study examined gene sequences from different sources and found that these genes were migrating from the hog lagoons to some groundwater wells. Although the study did not provide direct evidence, the team suspects the phenomenon occurred via horizontal gene transfer.
“Bacteria do not have to survive to pass on these mobile genetic elements,” Mackie explains. “If the genes are there, potentially they can get into the right organism at the right time and confer resistance to an antibiotic that’s being used to treat disease.”
Referring to the work as an environmental study, Mackie adds, “What is happening (regarding antibiotic use) will have a huge environmental footprint in the future, so even if we stop using tetracycline now, those resistance genes are not going to go away. Lining lagoons certainly helps, but you still need to dispose of that waste some way. If it’s done via land application, that’s a problem.”
It must be noted, however, that many genes that confer antibiotic resistance occur naturally in the environment. For example, tetracycline itself is a bacterial product, and naturally occurring bacteria may be resistant even without it being administered to animals or humans.
Without the benefit of scientific study and careful interpretation of the findings, some groups are likely to draw premature conclusions. It is critical that science be allowed to reveal the whys and wherefores of antibiotic resistance. However, scientific findings are not without controversy and require close and on-going examination.
“We feel the University of Illinois groundwater study wasn’t designed to find out if horizontal gene transfer was occurring,” says Liz Wagstrom, DVM, National Pork Board’s assistant vice president, science and technology. “In fact, their work demonstrated that properly designed and maintained lagoons made any chance of gene transfer occurring extremely small.”
According to Harry Snelson, DVM, American Association of Swine Veterinarians’ communications director, “The University of Illinois study concluded that properly lined lagoons did not leach tetracycline-resistant genes into the surrounding water supply to any greater degree than was found there naturally. Also, the study showed no difference in tetracycline-resistant genes in wells located in areas where manure was land-applied.”
Producers and swine veterinarians have long focused on assuring that antibiotics are used properly. The NPB’s Take Care: Use Antibiotics Responsibly program (see sidebar) and Pork Quality Assurance Plus are two programs designed to assist with that effort. Individual, on-farm staff training and monitoring programs are equally critical to the industry’s responsible use.
More research needed
“Obviously this (Illinois study) has potential consequences which need to be better understood,” Snelson adds. “There is need for significant research into the mechanisms by which resistance-gene transfer occurs and the potential implications. There’s also need for research to determine the sources of antimicrobial resistance in the human and animal populations, and the interactions between the two.”
The University of Illinois study helps provide a reliable foundation on which to base future studies. It provides important clues on the diversity and abundance of tetracycline-resistant genes found in a pork production environment. A similar study that examines tylosin will be presented next, Mackie says.
Antibiotics provide an important tool to reduce animal suffering and mortality. There’s also evidence that they improve the safety of the food supply by helping reduce certain pathogens. “It’s important that veterinarians and pork producers be able to retain the use of a variety of antimicrobial agents for effective disease control and treatment in pigs,” Snelson says. “Adherence to responsible antimicrobial use guidelines, as well as compliance with appropriate withdrawal periods, also is critical.”
Again, Wagstrom points to NPB’s Take Care: Use Antibiotics Responsibly program and the newly revised PQA Plus program as the industry’s commitment to highlighting the importance of using antibiotics judiciously. “Knowing and following the Responsible Use principles and guidelines is the single most important thing a producer can do to address this issue,” she adds. (See sidebar.)
Antibiotic resistance in bacteria is a highly complex natural phenomenon, and no single factor or study can be singled out as the definitive answer. Everyone must use antibiotics responsibly.
Bacteria will continue to do whatever is necessary to ensure their survival. Fortunately, science is making great strides in understanding and confronting antibiotic resistance.
Meanwhile, producers and consumer groups alike have the responsibility to heed what scientific research tells us — and to avoid presuming things it does not. They must neither hide from the findings nor jump to conclusions.
A key factor in the development of antibiotic resistance is the bacteria’s ability to adapt quickly to new challenges. Bacteria divide every few hours to reproduce, so they can evolve rapidly.
There are four mechanisms of antibiotic resistance:
1. Decreased cell wall permeability, which results in reduced uptake of antibiotics.
2. Increased efflux by pumping antibiotic out of the cell.
3. Enzyme action, which results in the antibiotic’s modification or degradation.
4. Modification of the antibiotic’s cellular target.
Bacteria also have the ability to mutate by making very slight changes in their genetic makeup. Even a single random genetic mutation to a resistance gene can greatly increase the bacteria’s ability to survive an antibiotic’s assault. Such a mutation will be passed on to following generations and quickly become dominant.
Bacteria also can acquire genes from each other by a process known as horizontal gene transfer. The DNA that provides antibiotic resistance can be packed into a single, easily exchanged mobile parcel. This means that bacteria can become resistant to a given antibiotic simply by acquiring one piece of DNA.
Prioritize Responsible Antibiotic Use
When it comes to antibiotic use, pork producers have a big responsibility. Careful planning and diligent supervision are necessary whenever antibiotics are used in production.
To that end, the National Pork Board has developed five principles to use antibiotics responsibly within the pork production system. Evaluate your operation based on these principles and see that staff members are fully informed of the following guidelines.
1. Take appropriate steps to decrease the need to apply antibiotics.
2. Assess the advantages and disadvantages of all antibiotic uses.
3. Use antibiotics only when they provide measurable benefits.
4. Complete the Pork Quality Assurance Plus program and fully implement the management practices outlined for the use of animal-health products in daily operations.
5. Observe the following Take Care Responsible Use guidelines:
- Use professional veterinary input for all medication decisions.
- Use antibiotics for treatment only when there is an appropriate clinical diagnosis.
- Limit antibiotic treatment to ill or at-risk animals in order to treat the fewest animals.
- Antibiotics that are important in treating antibiotic-resistant infections in human or veterinary medicine should be used in animals only after careful review and reasonable justification.
- It is illegal for producers to mix injectable or water medications together, including antibiotics.
- Minimize environmental exposure through proper handling and disposal of all animal-health products, including antibiotics.
The American Association of Swine Veterinarians offers these basic principles for prudent antibiotic use:
- Antibiotics are health-management tools which are licensed to enhance good husbandry practices to prevent and treat disease, and enhance production. They are a complement to good husbandry practices and should never be used to compensate for or mask bad farm and veterinary practices.
- Codes of good practices, quality assurance programs and education programs should promote responsible and prudent antibiotic use.
- Professional supervision, particularly by veterinarians, along with recordkeeping are essential in the use and control of antibiotic products.
- Antibiotics used for a specific therapy should be used for as short of a duration as possible, but for as long as needed, and at the appropriate dosage regimen. Always pay attention to label instructions.
- Continuously monitor the effects (positive and negative) of antibiotics in use in order to promptly adapt the use pattern.