In-Feed vs. In-Water Chlortetracycline Administration on the Fecal Prevalence of Virulence Genes and Pathotypes of Involved in Enteric Colibacillosis in Piglets.

Colibacillosis in nursery pigs, caused by (ETEC, EPEC, and STEC pathotypes), remains a major economic concern in the swine industry. This study evaluated the effects of in-feed or in-water chlortetracycline (CTC) administration on the fecal prevalence of virulence genes and pathotypes associated with colibacillosis. A total of 1296 weaned piglets (21 days old) were allocated to 48 pens (16 pens/treatment; 27 piglets/pen) and assigned randomly to no CTC, in-feed CTC, or in-water CTC groups. CTC was administered from days 0 to 14. Fecal samples from five piglets per pen on days 0, 14, and 28 were enriched, screened by 11-plex PCR, cultured for pathotypes, and tested for CTC susceptibility and tetracycline resistance genes. None of the 360 fecal samples or 3267 isolates were positive for or . Prevalence of (96.9%) and (92.8%) was highest. ETEC was the dominant pathotype (41.2%), with (29%) and (21.9%) as predominant enterotoxin genes. CTC administration had no significant effect on fecal prevalence of virulence genes or pathotypes ( > 0.05). and STEC were detected only at day 28, all harboring . All pathotypes were CTC-resistant, with as the predominant resistance gene.