Antibiotic use and resistance on dairy farms

by Stephen Wagner

Hayley Springer cut to the chase by answering the question “What is antibiotic resistance?” It is the ability of bacteria to resist the effects of an antibiotic that would otherwise kill it or stop its growth. This is due, she said, “to a change in the bacteria. People think it’s a change in the animal or a change in the drug, but it’s a change in the bacteria that causes the disease.”

She was speaking at the Dairy, Livestock (Cattle Congress) & Crops Compliance Conference at the Lebanon Valley (Pennsylvania) Expo Center. “Generally, we have lots of bacteria in a system and a few of them are drug resistant,” she explained. “Susceptible ones would be able to be killed. The others are drug resistant.” It ends with a bacteria population that’s harder to fight.

Who worries about animal agriculture? Parents who are trying to raise healthy kids. “Right now, there are an estimated two million illnesses and about 23,000 deaths from antibiotic-resistant illnesses in the United States,” Springer said. A projection for the year 2050 does not show all food-borne-related illnesses, but Africa and Asia, however, have incredibly high numbers of projections for mortality. “The two big drivers for that are tuberculosis and malaria,” she said. “That’s because there’s building resistance in both those organisms.

“Why do we need to address anti-microbial resistance on farms? We have evidence of it in beef, swine, poultry and dairy,” Springer said. “So, yes, we really do have anti-microbial resistance in ag.” Out of her own research, Springer showed a slide documenting the percentage of calves carrying E. coli resistant to various antibiotics. The slide showed a percentage of calves – nearly 100% – are carrying E. coli resistant to Ampicillin. “It is an early generation penicillin so I’m not surprised to see a lot of resistance there,” she noted. Next to that was Cefoxitin, a cephalosporin, a much stronger drug. After that came cefotaxime, an even stronger cephalosporin. Tetracycline is another that is very high. So is Streptomycin. “Ciprofloxacin is a last line treatment for salmonella in humans, particularly in children, because it’s a drug that doesn’t have as many side effects in young kids. We have very minimal resistance to that,” she said, the result of looking at 13 farms in Pennsylvania.

Now we come to the human risk of indirect disease. “This is a big concern,” Springer warned. “Extraintestinal pathogenic E. coli (ExPEC) cause disease outside of the intestinal tract. The most common disease in humans that would be caused by ExPEC would be urinary tract infections,” she explained. It also causes sepsis and meningitis. The focus on the UTI shows how it might possibly link back to the farm, and why it’s important to manage resistance on the farm as much as possible. UTIs in humans are derived from fecal flora. We know that’s where E. coli lives, and is the most common cause of UTIs. They get into the urinary tract and cause infection. How does this link back to agriculture? “Food provides the source for the natural flora in your gut,” Springer said. “Oral inoculation through our food is how we do get our fecal flora, so this is not that unfounded of a thought.”

Dr. Zachary Stromberg of the Los Alamos National Laboratory wrote in a paper that “we assessed whether fecal E. coli isolates from healthy production chickens could cause diseases in a chicken model of avian colibacillosis and three rodent models of ExPEC-associated human infections.” In 2017, according to Springer, “what they looked at was a UTI-related mouse model,” and pointed out what a kidney infection looks like. “This tells me it is a possibility that E. coli from animals could indirectly cause disease in people,” she stated.

Turning her attention to women with UTI E. coli infections in Canada, Springer saw these women had exposure to chickens. The list included processed or ground chicken, cooked or raw shellfish, cooked or ground beef, contact with chickens (or feces), contact with dogs (or feces), street carts or food trucks and travel in Asia. “One that I found really interesting was the consumption of any organic fruit,” she said. “There’s over eight times increased risk of having a UTI with greater than three antibiotic resistors. The reasoning behind this is the fertilizer for organic products: manure! They took this and linked it back to animal agriculture.” Springer sees this particular logic as being used to vilify animal agriculture. Much of the argument seems to center on organic agriculture. Springer noted, “People who are eating organic agriculture are a subset of our population with fairly specific demographics. This now excludes most of our lower socio-economic class of people because they cannot afford organic. There are a lot of other things that go into the choice of whether or not to eat organic.”

What is to be done about antibiotic resistance? “We can look at this from two different perspectives. This can either be a target on our backs or it can be a spotlight. I like to look at it as a spotlight. This is our opportunity to show CDC [Centers for Disease Control] that we know how to manage antibiotics on our farms and that we can effectively use antibiotics while still trying to reduce antimicrobial resistance,” Springer said. How can this be done? CDC might step in with some regulations. VFD [Veterinary Feed Directive] has been implemented because of antibiotic resistance.

“The other side,” said Springer, “is antibiotic stewardship. That means judicious use of antibiotics – the right drug at the right dose at the right duration.”

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