Project Summary

Dissemination of Resistance from Multi Drug-resistant (MDR) Generic E. coli to Salmonella in Dairy Calves and the Potential Role of Ruminal Protozoa

Principle Investigator(s):
Tom S. Edrington and Todd R. Callaway
U.S. Department of Agriculture, Agricultural Research Service
Completion Date:
May 2008



Previous research conducted by our laboratory and funded in part by the Beef Checkoff, investigated the incidence of MDR Salmonella in dairy cattle and reported that individual cattle, and most often calves, can shed multiple Salmonella serotypes that vary in the degree of antibiotic resistance.  More recently, we discovered a high incidence of a MDR generic E. coli in dairy calves.  Taken together, this suggests the generic E. coli population may be an important reservoir for MDR elements that can be spread to Salmonella, E. coli O157:H7 or other pathogenic organisms.  However, this MDR generic E. coli appears to be short-lived in the calf, decreasing in prevalence with age, while other generic E. coli persist.  We hypothesize that this is related to maturation and development of the digestive tract in the young ruminant, and if so, implies that interventions could be developed to eliminate the MDR generic E. coli at a younger age, thereby reducing the risk of resistance transfer to pathogenic bacteria. 

The stated objectives for this work were: 

  • Determine if MDR generic E. coli (in naturally colonized dairy calves) transfers resistance to inoculated strains of pan-susceptible Salmonella Newport and Reading. 
  • Examine the role of protozoa on resistance transfer and duration of fecal shedding of MDR generic E. coli in dairy calves.

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