US study hints at rising antibiotic resistance in cattle

By Aerin Einstein-Curtis contact

- Last updated on GMT

US study hints at rising antibiotic resistance in cattle

Related tags: Antibiotic resistance

Use of antibiotics in animal feed, treatment and other influences may be contributing to a trend of multi-antibiotic-resistant bacteria in some US feedlot cattle. 

Researchers at the University of Kansas said they have seen an increasing trend toward antibiotic-resistant forms of Mannheimia haemolytica​, a bacteria known as one of the primary causes of bovine respiratory disease (BRD) in cattle. Economic loss caused by the disease, including treatment, labor expenses and cattle death, has been estimated at more than $1 billion in the US.

Brian Lubbers, director of the microbiology laboratory at Kansas State University and assistant professor told FeedNavigator that, so far, most of the focus has been on antibiotic resistance in humans and less has been discussed in regard to multi-drug resistance bacteria in animal medicine.

Lubbers recently studied samples of lung tissue from cattle with BRD that were sent to the Kansas State Veterinary Diagnostic Laboratory between 2009 and 2011. During that period, the number of samples that contained bacteria isolates resistant to five or more antibiotics used to treat the disease grew from 5% to 35% and the amounts of multidrug resistant isolates grew from 42% to 63% by 2011.

Similarly, the numbers of isolates that were considered pan-susceptible, or that did not have any drug tolerance, dropped from about 34% in 2009 to about 17% by 2011.

The study looked at about 389 isolates spread throughout three years. However it also noted a limitation in that all the samples came from the same region of the US, specifically the area of Kansas and Nebraska.

Antibiotic use in cattle

The growth of drug-resistance bacteria in cattle probably has several origins, said Lubbers. It likely isn’t tied to only one factor, such as the use of antibiotics as a feed additive to promote animal growth and development.

Antibiotic resistance in bacteria is thought to spread through gene packets that can transfer from one bacterium to another, said the researcher.  

“Certainly antibiotic use could promote this,” ​he said. “But I don’t think it’s a direct one-to-one connection, there are other factors involved.”

But meeting the challenge of antibiotic resistance requires not only determining potential impacts on human health, but also maintaining the ability of veterinarians to treat bacterial infections in animals.

Lubbers said, right now, the only way to tackle antibiotic resistance in animal health is to use such drugs judiciously and correctly.

The widespread use of antibiotics in food producing animals is considered by organizations including the US Center for Disease Control (CDC) to contribute to the creation of antibiotic-resistance bacteria. The organization’s 2013 report Antibiotic Resistance Threats in the United States​, documented the issue at that time in the US and offered some plans for stewardship moving forward.

Those plans included phasing out the use of antibiotic growth promoters (AGPs) in animal production and tracking patterns of resistance.

The US Food and Drug Administration (FDA) supports a voluntary approach to limiting the indiscriminate use of antibiotics in feed.

In December 2013, that agency began implementing a plan to phase out the use of medically important antimicrobials in livestock by 2017, whereby then, it says, certain antibiotics will only be given to farm animals for therapeutic treatment, and, at the direction of a veterinarian.

In June last year, the FDA said all 26 drug manufacturers were fully engaging with this strategy.

What’s next

Lubbers is in the process of expanding the initial study to run for a longer period of time. Additionally, it also will look at more strains of bacteria known to cause pneumonia. A separate but related research project is set to examine the strains of antibiotic resistant bacteria found in healthy cattle. 

“All the bacteria that we have are from animals that are sick, so we’re actually working on another separate project to collect samples from healthy animals to see what kind of rates we’re seeing in those cows,”​ he said.

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