Dairy study reveals rising antibiotic resistance, produces new test to help treat mastitis

Diseases on dairy farms cost money and lives, and a new study from Cornell has found ways to save both.

cowsIt reveals rising antibiotic resistance of Klebsiella species on farms, an issue that threatens cattle welfare, food safety, and public health in the United States.

While adding to evidence that increasing antibiotic use on farms is driving up resistance, it also reveals effective management strategies to reduce contagion and has produced an innovative test enabling more targeted management and treatment.

The study focused on Klebsiella bacteria, a major cause of the udder infection mastitis, one of the most common and costly dairy cattle diseases in the United States. The new test resulting from the study can identify specific Klebsiella strains from milk samples and tell how likely they are to be persistent, virulent, and resistant to antibiotics.

“We’ve seen many Klebsiella outbreaks in New York, especially in the last two years,” said Dr. Paolo Moroni, associate director of the Animal Health Diagnostic Center at Cornell’s College of Veterinary Medicine. “With our new test farmers and veterinarians can choose the treatments that are most likely to work on the strains they face and reduce the use of antibiotics in cases where they won’t help.”

Bovine Klebsiella comes in two forms: environmental strains living in feces and the environment and host-adapted strains infecting cows’ udders. One in four animals contracting clinical Klebsiella mastitis dies within days. Many others are culled. Klebsiella can stay silent inside the udder, giving no warning signs and quietly spreading across a herd.

New test predicts antibiotic response

As part of a multistate research project yielding results with immediate application, Moroni led a team from the College’s Quality Milk Production Services, which runs 200,000 milk samples each year for the New York dairy industry. They collected Klebsiella strains from cattle across the Northeast.

Analyzing and comparing samples, they found several genes associated with antibiotic resistance and virulence. Many turned out to be mobile genetic elements, unanchored DNA that can move around the genome within and even between bacteria. These elements are generally associated with the spread of antibiotic resistance and other virulence factors.

By inventing a new system of profiling unique features of different Klebsiella strains based on their mobile genetic elements, Moroni’s team developed a test that can identify given strains and predict their virulence and response to antibiotics.

“Now when farmers find Klebsiella in the herd and ask ‘can I treat this,’ we can give a definitive answer,” said Moroni. “Even if it’s too late to successfully intervene, testing can help the decision-making process for future cases.”

Antibiotic resistance is growing

Klebsiella can affect humans who come in contact with it, including farm workers and people who drink raw milk. The study showed that most of today’s bovine strains are already resistant to almost all antibiotic treatments.

“The more antibiotics used in cows, the more difficult it becomes to treat Klebsiella infections,” said Moroni. “The high resistance levels we’ve seen point to extensive antibiotic use, rather than implementing management strategies to control pathogens on farms.

“We used to have more small farms, but there’s been a sharp rise in the number of bigger farms with more cows,” said Moroni. “That’s changing how they’re milked and housed. Cows used to be housed in single stalls dedicated to individual animals, now large farms bed cows in groups and herd management practices have changed as well.”

Management solutions

The study revealed several actions farmers can take to prevent or control contagion without antibiotics. Moroni says farmers can reduce pathogens by:

  • Choosing inorganic bedding such as clean sand, as more bacteria grow in organic bedding and flooring materials like sawdust
  • Keeping barns and bedding clean and dry
  • Reducing over-crowding of group pens (fewer cows per stall)
  • Cleaning manure from stalls several times daily

“Improving management practices will lower mastitis rates, reduce the need for antibiotic use, advance animal health and milk quality, and improve both the economic outlook for dairies and overall public health,” said Moroni.