Résistance à la tétracycline et diversité génétique d’Escherichia coli isolés de porcs biologiques et de porcs conventionnels

Summary

The objectives of this study were to assess the prevalence, tetracycline resistance level and genetic diversity of Escherichia coli isolated from organic pigs in comparison with conventional pigs. 25 organic and 25 conventional herds were considered in one slaughterhouse from April to October 2012. Colon content of 2 pigs per herd was sampled. For each pig, E. coli and tetracycline resistant E. coli (TET+E. coli) were enumerated. Level of tetracycline resistance was then calculated. Isolates were typed by PFGE using XbaI enzyme.
E. coli was detected for all the organic (n=50) and conventional pigs (n=50). TET+E. coli was detected for 49 organic (98%) and 48 conventional pigs (96%). The number of E. coli per gram of colon content was significantly higher for conventional (6.81 log10 UFC/g) than for organic pigs (6.19 log10 UFC/g) as well as the number of TET+E. coli with 6.33 log10 UFC/g for conventional pigs and 5.68 log10 UFC/g for organic pigs. Finally, the level of tetracycline resistance was also significantly higher (p=0.0033) for conventional (57.4%) than for organic pigs (37.9%). PFGE was carried out on 374 E. coli; they were distributed in 275 pulsotypes. The genetic diversity was very high (Dvalue=0.997). No pulsotype was common to both organic and conventional pigs.
Results suggest that farm managements may have an impact on the amount of E. coli excreted and on their antibiotic resistance. However, it is difficult to estimate the impact on human health with 0.65 log10 UFC/g difference between the two productions. Diversity of strains is so high that it is difficult to associate strains to a production.