Objective To isolate and identify Escherichia coli (E. coli) from the intestinal contents of dead piglets, and to evaluate its virulence, drug resistance, and pathogenicity. This study aims to investigate the etiology of yellowish-white diarrhea in piglets on a farm in Fujian Province, thereby providing a basis for precise clinical medication and effective prevention and control.

Method Intestinal contents were collected from diarrheic deceased piglets. Pathogen isolation and identification were performed using selective culture, Gram staining, biochemical tests, 16S rRNA gene amplification, and serotyping. Virulence and resistance characteristics were analyzed through virulence gene detection, resistance gene detection, antimicrobial susceptibility testing, and mouse pathogenicity testing.

Result A pathogenic strain was isolated, which formed red colonies on MacConkey (MAC) agar and pale yellow colonies on xylose lysine deoxycholate (XLD) agar. Gram staining revealed Gram-negative short rods. 16S rRNA gene sequencing showed ＞99% sequence similarity to E.coli sequences in GenBank, confirming its identification as E. coli. Serotyping identified it as O2. Virulence gene detection showed the strain carried irp2, iucD, and sta genes. Resistance gene detection revealed it simultaneously harbored 11 resistance genes, including those for quinolones, tetracyclines, β-lactams, macrolides, phenicols, and sulfonamides. Antimicrobial susceptibility testing demonstrated resistance to 15 agents including ofloxacin, streptomycin, ampicillin, tetracycline, erythromycin, lincomycin, and sulfisoxazole, while exhibiting sensitivity to amikacin and spectinomycin. Mouse pathogenicity testing confirmed the isolate was pathogenic, with a median lethal dose (LD₅₀) of 1.60×10⁸ CFU.

Conclusion This study isolated an O2 serotype diarrheagenic E.coli strain from piglets in a large-scale pig farm in Fujian Province. The strain carries multiple virulence genes, exhibits severe multidrug resistance, and is highly pathogenic, providing important insights for the monitoring and control of colibacillosis in the Fujian region.