From Merck Animal Health's BRD Report: From the Fence Post. With this post, we begin a series that focuses on understanding antibiotic resistance, defining what antibiotic stewardship means and how cattle producers can be better stewards of antibiotic use. Brian Lubbers, D.V.M., Ph.D., Diplomate ACVCP, director of the Microbial Surveillance Lab, a unit of the Kansas State Veterinary Diagnostic Laboratory, is a contributor for this series.

Antibiotic resistance is a natural phenomenon. Resistance itself is a property, a characteristic of bacteria. Knowing that, some might say there’s nothing that we as producers or veterinarians can do to stop resistance – it’s going to happen anyway. But that’s not the case, and we need to talk about what role we can play in helping alleviate the pressure antibiotics put on increasing resistance.

Why is antibiotic resistance important? Using antibiotics has the potential to enhance a resistant population within an animal. It’s the same for humans – every time someone takes an antibiotic, they are potentially enhancing resistance in that population of bacteria as well. A lot of focus is on the relationship between antibiotic use in animal agriculture and potential human resistance, but another area that doesn’t get as much attention is the impact of multi-drug resistance in livestock.

Take bovine respiratory disease (BRD) for example. BRD is the most costly disease in beef cattle in the U.S.¹ There are four bacterial agents that are most often associated with BRD: Mannheimia haemolytica, Pasteurella multocida, Histophilus somni and Mycoplasma bovis.

The amount of antimicrobial resistance in BRD bacteria hasn’t been studied very well, so we decided to take a closer look in the Kansas State Veterinary Diagnostic Lab – examining bovine lung tissue samples that were submitted over a three-year period. We found that more than 60 percent of Mannheimia haemolytica isolates (the primary bacterial agent in BRD) were resistant to three or more types of antibiotics commonly used to treat BRD. Of that 60 percent, half were resistant to five of the antibiotics used to treat BRD.

To put that in perspective, there are only about six classes of antimicrobials used in BRD treatment. When the bacteria become multi-drug resistant, our choices of effective antibiotics become severely limited for treating cases of BRD.

Here’s what we know: antibiotic resistance is a real, natural phenomenon. It’s also very complex and not fully understood. As antibiotics continue to be used in both animal agriculture and human medicine, the potential for resistance will increase. Meanwhile, the number of new antibiotics brought to market is declining.

Our role is to better understand antibiotic stewardship and what part we should be playing in that initiative. Learn more in the next installment of this series.