Occurrence of ESBL-E. coli in feces of dairy calves and nipples of teat buckets for calves before and after automatic cleaning in two dairy farms.

Extended-spectrum β-lactamase (ESBL)-producing Escherichia (E.) coli are highly prevalent in dairy calves. In calf housing, the feeding equipment can function as a reservoir, thereby constituting a risk factor for the dissemination of ESBL-E. coli. The aim of this present study was to determine if ESBL-E. coli can be detected on the inner surface of teat buckets for calves and to evaluate if an automatic wash system specifically designed for teat buckets is suitable to eliminate existing ESBL-E. coli from the surfaces. Fecal samples from calves (aged three to 14 days) and teat swabs (before and after cleaning) on two farms were analyzed. Prior to cleaning, nipple contamination was detected on both farms on different levels. Automated cleaning significantly reduced contamination (P < 0.001). Whole-genome sequencing revealed close genetic similarities between fecal and nipple isolates, indicating transmission between calves and feeding equipment. Although the automatic cleaning significantly reduced bacterial contamination in teat buckets, ESBL-E. coli were detected in all calves (40/40), suggesting additional farm-level transmission routes.