The Centers for Disease Control & Prevention (CDC) issued an alarming report in April 2018 about a superbug nicknamed “nightmare bacteria”, scientifically named Carbapenem-Resistant Enterobacteriaceae (CRE), that is resistant to the antibiotic developed to eradicate it. To give you a point of reference, you are probably more familiar with other superbugs such as Methicillin-Resistant Staphylococcus aureus (MRSA) in people and Methicillin-Resistant Staphylococcus pseudointermedius in pets (MRSP).
While the CDC could have focused on a number of superbugs, the organization chose to focus on carbapenemase-producing strains for this study, in part because of their propensity to spread and their establishment in many U.S. states. The study results illustrated that 1 in 10 (11%) people were asymptomatic carriers of CRE, meaning they can spread the bacteria within the community. One expert called it, “human mosquitoes”.
So, the notion that superbugs are only contained to hospital settings is false. Indeed, it is well-known that MRSA, MRSP, and CRE have breached the hospital/veterinary community boundary.
Fortunately, the CDC launched an ambitious defensive CRE containment strategy. So, what can we do offensively to help combat these superbugs for us and our companion pets?
First and foremost, you could limit the amount of antibiotics you and your pets take. This is not saying to avoid taking an antibiotic if it is medically necessary. However, the doctor or veterinarian needs to complete bacterial cultures to ensure the right antibiotic is being prescribed for the specific pathogenic bacterium. This helps avoid broad-spectrum antibiotics, which are more likely to spread resistance compared to narrow-spectrum ones.
The Antibiotic Stats
Over the past several years, many US agencies have worked together to limit antimicrobial drug use in humans and livestock. (Remember: antibiotics are only one type of antimicrobials.) Has it been effective?
According to the CDC in 2024, at least 28% of antibiotics prescribed in outpatient settings are not needed. Overall, this number represents a downward trend over the 20 years. Of course, we can do better.
You might be thinking to yourself, “What about pets and livestock?”
That’s a good question.
In 2020, the University of Minnesota worked with 14 other veterinary teaching hospitals (VTHs) from all regions of the country to figure out the prevalence of antibiotic use at their facilities. They measured one day of companion dog or cat care. The departments of primary care, internal medicine, surgery, emergency and critical care, and urgent care were included. Of the 64.5% (285/442) of antibiotics prescribed for systemic administration intended for infection treatment: 28.1% (80/285) were prescribed for confirmed infections, 61.1% (174/285) for suspected infections, and 10.9% (31/285) when no evidence of infection was recorded in the medical record.
For years, feed animals were not given antibiotics to treat an actual bacterial infection. Concentrated animal feeding operations (CAFO) were notorious for continuously giving non-veterinary prescribed, over-the-counter (OTC) antibiotics for growth promotion and as a prophylaxis to stop the potential spread of diseases. Puppy mill puppies were also given antibiotics prophylactically. Now, we are reaping the harmful effects as numerous studies have shown that the bacteria are building up resistance to antibiotics due to these practices.
Every so often over the past 45 years, the U.S. Food and Drug Administration (FDA) has limited or banned the use of certain antibiotics in feed animals or in one particular species.
Instead of the aforementioned “plugging holes” approach, the agency developed a 5-year Veterinary Stewardship Plan (2018-2023) to limit the emergence of antimicrobial resistance. The changes were not sweeping, but are a positive step-by-step approach.
As of mid-2023, all medically important antimicrobials approved for use in both food-producing and companion animals were no longer available OTC. Food producers would need a valid veterinarian-client-patient relationship (VCPR) with a licensed veterinarian. The VCPR does not mean that producers must purchase the drugs from their veterinarian, but it does mean that the distribution of antibiotics would require a prescription from the veterinarian with whom they have a valid VCPR to purchase the drugs.
At the end of 2023, the FDA announced that sales of medically important antimicrobial drugs approved for feed animals were down 36% in 2022 compared to a record high in 2015. Although, there is a slight increase in 2022 compared to 2020 and 2021. Of course, this fluctuation could be due to the pandemic.
Remember when the CDC issued a report concerning the spread of antibiotic-resistant Campylobacter jejuni bacteria from pet store puppies to humans in 2018? The large-scale commercial breeder “puppy mill” industry is not as well-regulated as livestock. Supposedly, less than one-third of these breeders in the United States are listed with the U.S. Department of Agriculture (USDA) according to the Humane Society of the United States. Ostensibly, the USDA regulated large-scale breeders will also be held to the new FDA standards.
To gauge the mid-2023 realignment of the status of these medically important antimicrobials and the entirety of the stewardship plan, we believe we will need data from 2024 and 2025 to see if the efforts made a significant impact in reducing usage.
Non-Medically Important Antimicrobials
Of course, we wonder about what is considered as non-medically important antimicrobials.
One such example is the ionophores (antibiotic) for cattle to promote growth. These can still be purchased OTC to a cow’s diet because they are not considered medically important to human health.
Another example is dewormers (i.e. antiparasitics) such as ivermectin.
H. Morgan Scott of Texas A&M University and colleagues penned a critical review in 2020 of the FDA’s plans:
“While ‘over‐the‐counter’ formulations of in‐feed and in‐water antibiotics for food‐producing animals have completely disappeared, veterinarians have been afforded a much greater role in decision making through Veterinary Feed Directives. However, the agency has approved new uses of medically important antibiotics in animal agriculture that appear counterintuitive to the goal of reducing antibiotic use.”
All we have to say is that time will tell.
The Overlooked Residue
You might be thinking to yourself, “Oh good; I only buy antibiotic-free meat, milk and poultry.”
That’s great; but you may not be aware of the often overlooked incidental and continuous ingestion of antibiotic residue.
One safeguard is the U.S. National Residue Program (NRP) for Meat, Poultry, and Egg Products – it is administered by the USDA’s Food Safety and Inspection Service (FSIS). This inspection team samples animal products for all sorts of chemicals from antibiotics to pesticides. This is not to say that the animals were never given antibiotics, but that the withdrawal period before slaughter was possibly shortened if the substances were found. In any event, this type of oversight is needed and good.
But, we need to consider the environmental impact and cyclical nature of manure.
Like humans, animals do not fully metabolize antibiotics. Approximately 75–80% of tetracyclines, 60% of lincosamides, and 50–90% of macrolides are excreted unchanged, and they can persist and accumulate in the environment.
Animals are not only excreting the antibiotics, but they are also excreting antibiotic-resistant bacteria and antibiotic-resistant genes.
This manure leaches into waterways or is often used for crop production. Therefore, there is a continuous ingestion of antibiotics and antibiotic-resistant bacteria by all humans, animals, and plants at some level.
Of course, the reduction of use should ostensibly reduce residue and resistance. When will the impact be noticeable? In our estimation, a retrospective review should be completed in 2033.
References
Scott, H Morgan et al. “Critically important antibiotics: criteria and approaches for measuring and reducing their use in food animal agriculture.” Annals of the New York Academy of Sciences vol. 1441,1 (2019): 8-16. doi:10.1111/nyas.14058, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6850619/.
Checcucci, Alice et al. “Exploring the Animal Waste Resistome: The Spread of Antimicrobial Resistance Genes Through the Use of Livestock Manure.” Frontiers in microbiology vol. 11 1416. 22 Jul. 2020, doi:10.3389/fmicb.2020.01416, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7387501/.
Cadena, Marlynn et al. “Tetracycline and Sulfonamide Antibiotic Resistance Genes in Soils From Nebraska Organic Farming Operations.” Frontiers in microbiology vol. 9 1283. 28 Jun. 2018, doi:10.3389/fmicb.2018.01283, https://pmc.ncbi.nlm.nih.gov/articles/PMC6033193/.
McKinney, Chad W et al. “Occurrence and abundance of antibiotic resistance genes in agricultural soil receiving dairy manure.” FEMS microbiology ecology vol. 94,3 (2018): 10.1093/femsec/fiy010. doi:10.1093/femsec/fiy010, https://pubmed.ncbi.nlm.nih.gov/29360961/.
Van Epps, Amanda, and Lee Blaney. “Antibiotic Residues in Animal Waste: Occurrence and Degradation in Conventional Agricultural Waste Management Practices.” Current Pollution Reports, vol. 2, no. 3, Sept. 2016, pp. 135–155, https://link.springer.com/article/10.1007/s40726-016-0037-1.
Woodworth KR, Walters MS, Weiner LM, et al. “Containment of Novel Multidrug-Resistant Organisms and Resistance Mechanisms — United States, 2006–2017.” Vital Signs MMWR Morb Mortal Wkly Rep. 2018;67:396-401. DOI: http://dx.doi.org/10.15585/mmwr.mm6713e1, https://www.cdc.gov/mmwr/volumes/67/wr/mm6713e1.htm.
Originally Published: April 22, 2018
Updated: October 20, 2024