Changes in Fecal Carriage of Extended-Spectrum -Lactamase Producing Enterobacterales in Dutch Veal Calves by Clonal Spread of .

This study aimed to characterize the changes in fecal carriage of Extended-Spectrum β-Lactamase (ESBL) producing Enterobacterales (ESBL-PE) in a single Dutch veal calves. During the rearing period at the Dutch veal farm, a decrease in fecal carriage of cefotaxime-resistant isolates was observed after 2 weeks at the veal farm, while an increase of cefotaxime-resistant isolates was demonstrated. and were isolated from rectal swabs collected from 110 veal calves in week 2, 6, 10, 18, and 24 after their arrival at the farm. ESBL-PE isolates were selectively cultured and identified by MALDI-TOF. ESBL genes were characterized by RT-PCR, PCRs, and amplicon sequencing. A total of 80 and 174 strains were isolated from 104 out of 110 veal calves. The prevalence of ESBL- decreased from week 2 (61%) to week 6 (7%), while an unexpected increase in ESBL- colonization was detected in week 6 (80%). The predominant ESBL genes detected in isolates were and the non-ESBL gene , while in gene was detected in all isolates. Four cefotaxime-resistant isolates were randomly selected and characterized in deep by transformation, PCR-based replicon typing, and whole-genome sequencing (WGS). The clonal relatedness of a subgroup of nine animals carrying ESBL genes was investigated by Multi Locus sequence typing (MLST). In four ESBL- isolates, was located on IncFII and IncFII plasmid replicons and the isolates were multi-drug resistant (MDR). MLST demonstrated a clonal spread of ESBL- ST107. To the best of our knowledge, this is the first study to report a change in fecal carriage of ESBL-PE over time in the same veal calf during the rearing period.