When we think of food poisoning, undercooked chicken is usually the first culprit that comes to mind. But new research from the University of Prince Edward Island suggests another major agricultural player needs closer monitoring: the dairy industry.

A 2026 Master's thesis by Lauren E. MacNeil provides a comprehensive look at the prevalence of Campylobacter (the leading bacterial cause of foodborne illness globally) within Canadian dairy cattle. The findings underscore a pressing need for integrated surveillance to protect both public health and the agricultural economy.

The Economic and Industrial Stakes

Campylobacter infections are no small issue. Symptoms range from severe abdominal pain and bloody diarrhea to long-term chronic complications like Guillain-Barré syndrome and reactive arthritis. Beyond the human toll, the economic impact is staggering. In the United States alone, foodborne illnesses cost an estimated $17.6 billion annually in medical expenses and lost wages, with Campylobacter accounting for $2.2 billion of that total.

For the agricultural industry, the asymptomatic carriage of these bacteria in livestock is a silent threat. While the animals rarely get sick, the pathogens can enter the human food chain (often through raw or unpasteurized milk) and cause severe outbreaks. The World Health Organization has declared antimicrobial resistance (AMR), which is the ability of bacteria to evolve and survive the drugs designed to kill them, as one of the top ten threats to global public health. If treatments fail, the economic and health burdens multiply.

The Findings: A Hidden Reservoir

MacNeil’s study analyzed 4,748 fecal samples across five Canadian livestock commodities: dairy cattle, feedlot cattle, grower-finisher swine, turkeys, and broiler chickens.

The results were eye-opening. Campylobacter was recovered from 54.0% of the pooled dairy cattle samples. Even more striking, in 2019, 95.0% of the tested dairy herds had at least one sample test positive for the bacteria.

The most common strain found in the dairy cattle was Campylobacter jejuni (C. jejuni). This is highly significant for public health, as C. jejuni is responsible for approximately 90% to 95% of all human Campylobacter infections.

The Resistance Problem

The research didn't just look for the bacteria; it tested how well they could survive antibiotics. The study found that most C. jejuni isolates from the dairy cattle were resistant to tetracycline and quinolone drugs. This is concerning because fluoroquinolones (a type of quinolone) and macrolides are the primary drugs used to treat severe Campylobacter infections in humans.

To understand how the bacteria were surviving, the researchers used a high-tech approach called Whole Genome Sequencing (WGS). WGS is essentially mapping the entire DNA of the bacteria to find specific "resistance genes". They found a strong match: the bacteria carrying the tet(O) gene and specific mutations (like gyrA) were the exact same ones surviving the antibiotic treatments in the lab.

The Good News

While the prevalence of the bacteria and certain drug resistances are high, there is a silver lining. Multi-drug resistance (MDR) (defined as bacteria being resistant to three or more classes of antibiotics) was extremely rare in the dairy cattle. Only 0.3% of the C. jejuni dairy isolates exhibited MDR, a stark contrast to higher MDR rates found in swine and feedlot cattle.

Looking Forward

MacNeil's research does not suggest that dairy products are unsafe, especially when pasteurized. Instead, it highlights a critical blind spot in how the agricultural industry monitors foodborne pathogens. Historically, the poultry industry has borne the brunt of Campylobacter surveillance. This new data proves that dairy cattle are a significant reservoir and must be included in national monitoring programs to track and mitigate the rise of antibiotic resistant "superbugs".