New antibiotic resistance gene in Washington dairy cattle

By Margaret Davis


E coli bacteria are normally found in feces and environments of dairy cattle and calves, so monitoring E coli is a good way to learn about antibiotic resistance on dairies. A new gene, called blaCTX-M for resistance to ceftiofur was first detected in Washington State in 2011 (Table 1). Previously, the earliest detection of E coli with blaCTX-M in U.S. cattle was reported by Ohio State in 2009 from fecal samples collected from dairy cattle. In the early 2000’s these bacteria were prevalent in human infections in Canada, and the first human infection was reported in Washington State in 2001-2002.

Table 1
Results of blaCMY-2 and blaCTX-M PCR of E. coli from cattle feces in the Pacific Northwest.
YearTotal number
of isolated
bacteria tested
of farms
% blaCMY-2
(95% CI)
% blaCTX-M
(95% CI)
2002-200394688.2 (79.5 - 93.7)0 (0 - 3.9)
200864470.3 (57.4 - 81.9)0 (0 - 7.1)
201193265.6 (55.5 - 74.9)10.8 (5.6 - 19.4)
2012*7873031.1 (27.9 - 34.5)12.4 (10.2 - 15.0)

*In 2012, bacteria were collected without using antibiotics to select for resistant ones, as was done for the previous years. So we can’t conclude that the prevalence of blaCMY-2 went down between 2011 and 2012.

Our research

In 2012, fecal samples from an average of 39 calves on each of 30 dairy farms in Washington State were collected and information about the farms and management practices gathered.

  • Total number of fecals samples? Number of isolates?
  • A gene that causes resistance to ceftiofur and ampicillin-clavulanic acid (called blaCMY-2) was present in > 90% ofthe fecal samples from 25/30 farms.
  • The new gene (blaCTX-M) was present in > 90% of fecal samples from 9/30 farms.
    • 28/30 farms had some blaCTX-M

From a survey of management factors, some potential risk factors emerged that were associated with a high prevalence of the new resistance factor blaCTX-M :

  1. Herd size: Larger herds had higher prevalence.
  2. Fly control: The use of residual fly sprays for insect control was associated with lower prevalence. (Table 2)
  3. Any recent animal movement onto the farm was associated with higher prevalence. (Table 3)
  4. Frequency of adding new bedding to calf hutches: On large herds with less than weekly addition of new bedding had higher prevalence. (Table 4)

Table 2
Herd size and use of residual sprays for fly control. The prevalence of bacteria from calves with the new resistance factor, blaCTX-M according to the herd size in terms of number of adult cows and whether the farms used residual fly sprays for fly control.

Table 3
Animal movement onto the farm. The prevalence of bacteria from calves with the new resistance factor, blaCTX-M, according to whether or not animals were moved onto the farm in the previous 6 months. Animal movements included purchase of bulls or cows, and bringing heifers back on to the farm after being raised elsewhere.

Table 4
Herd size, and frequency that new bedding is added to calf hutches.

The prevalence of bacteria from calves with the new resistance factor, blaCTX-M, according to the herd size in terms of number of adult cows and how frequently new bedding was added to the calf hutches.


This novel resistance factor rapidly became widespread globally. Although antibiotic use may promote the emergence of new resistance factors, allowing for dissemination of the bacteria is also important. Biosecurity measures like fly control, limiting animal movement and hutch management may help to prevent dissemination of blaCTX-M in the E. coli of cattle.


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