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Keywords:

  • food safety;
  • Salmonella ;
  • Yersinia

Abstract

Aims

The objective of this study was to investigate the survival of Salmonella and Yersinia enterocolitica strains in pig slurry and evaluate urea and ammonia as disinfection strategies.

Methods and Results

Salmonella Anatum, Salmonella Derby, Salmonella Typhimurium DT19 and Y. enterocolitica bioserotypes 4, O:3, 2, O:5,27 and 1A, O:6,30 were selectively marked by insertion of the plasmid, pGLO encoding for green fluorescent protein and for ampicillin resistance. Strain cocktails were inoculated into fresh pig slurry (control), slurry treated with urea [final concentration 2% w/w, (0·33 mol l−1)] and slurry treated with ammonia [final concentration 0·5% w/w, (0·3 mol l−1)] and stored at 4, 14 and 25°C. Bacterial counts were determined at regular intervals on xylose lysine deoxycholate agar (XLD), and XLD supplemented with ampicillin (0·1 mg ml−1) and arabinose (0·6 mg ml−1) for Salmonella and cefsulodin-irgasan-novobiocin agar (CIN) and CIN supplemented with ampicillin and arabinose for Y. enterocolitica. The pH of the control-, urea- and ammonia-treated samples ranged from 7·1 to 7·7, 8·8 to 8·9 and 8·0 to 8·3, respectively. Salmonella D4 values ranged from 2·71 to 21·29 days, D14 values from 2·72 to 11·62 days and D25 values from 1·76 to 6·85 days. The equivalent D values ranges for the Y. enterocolitica strains were 3·7–19·23, 1·8–16·67 and 1·63–7·09 days, respectively. Treatment significantly (P < 0·01) affected D values with control > ammonia > urea, as did incubation temperature; 4 > 14 > 25°C.

Conclusions

Urea and to a lesser extent ammonia may be used to disinfect Salmonella- and/or Y. enterocolitica-contaminated pig slurry, decreasing the storage time required while increasing its fertilizer value.

Significance and Impact of the Study

This study presents data supporting the treatment of pig slurry to kill important zoonotic agents, thereby reducing environmental contamination, cross-infection of other animals and decreasing zoonotic disease in the food chain.