Decreased Resistance to Broad-Spectrum Cephalosporin in Escherichia coli from Healthy Broilers at Farms in Japan After Voluntary Withdrawal of Ceftiofur

The high prevalence of broad-spectrum cephalosporin (BSC) resistance in Escherichia coli isolates from healthy broilers at farms is a source of grave concern in Japan. In an effort to solve this problem, the off-label use of ceftiofur (CTF) at hatcheries was voluntarily withdrawn around March 2012. The objective of this study was to assess the effect of the voluntary withdrawal on the prevalence of BSC resistance in E. coli from healthy broilers at farms. A total of 693 E. coli isolates collected from 362 fecal samples of healthy broilers at farms between 2010 and 2013 were examined to determine their antimicrobial resistance profiles and β-lactamase genes. β-Lactamase genes were characterized by polymerase chain reaction and sequencing. BSC resistance was detected in 84 of the 693 E. coli isolates (12.1%) from healthy broilers between 2010 and 2013. The percentage of BSC-resistant E. coli isolates was significantly decreased: from 16.4% (32/195) in 2010 and 16.8% (27/161) in 2011 to 9.2% (19/206) in 2012 and 4.6% (6/131) in 2013 (2010 versus 2012: p=0.024, 2010 versus 2013: p=0.001, 2011 versus 2012: p=0.038, and 2011 versus 2013: p=0.001). Regarding ß-lactamase genes, 58 of the 84 BSC-resistant E. coli isolates (69.0%) harbored blaCMY-2. The prevalence of BSC resistance in E. coli isolated from healthy broilers at farms was markedly decreased within a year after the voluntary withdrawal from CTF use at hatcheries. This indicates that BSC resistance in E. coli isolates from broilers could be controlled by restricting the use of CTF at the hatchery level.