4.2 Emergence of ceftiofur-resistant S. Heidelberg in broilers
Let’s look at how this ceftiofur resistance emerged in salmonellae in broiler chickens.
The major factor contributing to the emergence of ceftiofur resistance in Salmonella organisms carried by broilers was found to be off-label use of ceftiofur in hatcheries that produce broiler chicks during 2003–4. Small doses of ceftiofur were injected into thousands of eggs immediately prior to hatching and/or into newly hatched chicks to prevent the occurrence of E. coli yolk sac infections (Dutil et al., 2010). This is an example of prophylactic use of antimicrobials to prevent the occurrence of clinical disease and mortality.
At the same time, an increased prevalence of ceftiofur resistance was detected in E. coli as well as in Salmonella isolates from broilers, which was likely to be associated with the same driver: prophylactic use of ceftiofur in broiler hatcheries. This was an additional concern because ceftiofur resistance is carried on a mobile genetic element and can potentially be transmitted from one species of bacteria to another.