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<p>Routine diagnostics for neonatal calf diarrhea largely target K99 (F5) <i>Escherichia coli</i>, overlooking atypical lineages carrying the enteroaggregative heat-stable toxin 1 (EAST1; <i>astA</i>). This study determined <i>astA</i> prevalence in K99-negative diarrheic calves and characterized the isolates, applying a stringent definition for true enteric–extraintestinal hybrids. Rectal swabs from 239 diarrheic calves (≤ 28 days) referred to Kafkas University Animal Hospital were screened by rapid test/PCR for K99 and PCR for <i>astA</i>. Isolates were clonally resolved by ERIC-PCR and characterized via PCR for enteric and ExPEC/ColV markers, Clermont phylogrouping, O-genotyping, and disk diffusion test, with DDST confirmation for ESBL. Associations were assessed by Fisher’s exact test with odds ratios (OR) and 95% CI. K99 was absent in all samples; <i>astA</i> was detected in 19.7% (47/239) of cultures, yielding 44 distinct strains. F17 was carried by 16/44 (36.4%; 15 F17a, 1 F17c); ColV plasmid markers occurred at 25.0% and <i>clpG</i> in 20.5%. Two isolates (4.5%) met the strict hybrid definition. Phylogroup A dominated (40.9%), with O101 (38.6%) clustered entirely within it. F17 was strongly linked to Phylogroup A (OR 125.0, 95% CI 11.9–1313.3; <i>P</i> &lt; 0.001). Phylogroup B1 was associated with ceftazidime resistance (OR 39.3, <i>P</i> &lt; 0.001) and complete ColV carriage (OR 12.9, <i>P</i> = 0.007). Resistance was extensive (CIP and TE 93.2%, CAZ 38.6%); 29.5% were ESBL-positive and 93.2% MDR. <i>astA</i>-positive <i>E. coli</i> comprise dual-axis populations, including high-risk MDR/ESBL clones in Phylogroup B1, supporting the need for broader diagnostic panels and updated preventive strategies.</p>

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Hybrid enteric-extraintestinal lineages in astA-positive Escherichia coli: Molecular characterization and high-risk MDR clones in Neonatal Calves

  • 期刊论文

  • 发表日期：

    2026年7月16日

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  • Mustafa Reha Coşkun,
  • Mert Sezer,
  • Yusuf Umut Batı,
  • Enes Akyüz,
  • Yunus Emre Şahin,
  • Nazlıcan Yerli

摘要

Routine diagnostics for neonatal calf diarrhea largely target K99 (F5) Escherichia coli, overlooking atypical lineages carrying the enteroaggregative heat-stable toxin 1 (EAST1; astA). This study determined astA prevalence in K99-negative diarrheic calves and characterized the isolates, applying a stringent definition for true enteric–extraintestinal hybrids. Rectal swabs from 239 diarrheic calves (≤ 28 days) referred to Kafkas University Animal Hospital were screened by rapid test/PCR for K99 and PCR for astA. Isolates were clonally resolved by ERIC-PCR and characterized via PCR for enteric and ExPEC/ColV markers, Clermont phylogrouping, O-genotyping, and disk diffusion test, with DDST confirmation for ESBL. Associations were assessed by Fisher’s exact test with odds ratios (OR) and 95% CI. K99 was absent in all samples; astA was detected in 19.7% (47/239) of cultures, yielding 44 distinct strains. F17 was carried by 16/44 (36.4%; 15 F17a, 1 F17c); ColV plasmid markers occurred at 25.0% and clpG in 20.5%. Two isolates (4.5%) met the strict hybrid definition. Phylogroup A dominated (40.9%), with O101 (38.6%) clustered entirely within it. F17 was strongly linked to Phylogroup A (OR 125.0, 95% CI 11.9–1313.3; P < 0.001). Phylogroup B1 was associated with ceftazidime resistance (OR 39.3, P < 0.001) and complete ColV carriage (OR 12.9, P = 0.007). Resistance was extensive (CIP and TE 93.2%, CAZ 38.6%); 29.5% were ESBL-positive and 93.2% MDR. astA-positive E. coli comprise dual-axis populations, including high-risk MDR/ESBL clones in Phylogroup B1, supporting the need for broader diagnostic panels and updated preventive strategies.