Comparison of organic and conventional pig productions on prevalence, antibiotic resistance and genetic diversity of Escherichia coli

In this part of a CORE Organic II funded project, the objectives were 1) to assess the occurrence of E. coli in organic pig production, in comparison with conventional production, 2) to estimate the E. coli tetracycline resistance level in pig of the two productions, and 3) to evaluate the genetic diversity of strains isolated from these two productions. 25 organic herds and 25 conventional herds were considered in one slaughterhouse from April to October 2012. Two pigs per herds were considered. For each pig, numeration of Escherichia coli and of tetracycline resistant E. coli (TET+E.coli), were realized from colon content. Level of tetracycline resistance for each sample was then determined by the % of tetracycline resistant E. coli from the total number of E. coli. From colon content, on the 100 sampled pigs, E. coli was detected for all the organic pigs (n=50) and conventional (n=50). TET+E.coli was detected for 49 organic pigs (98%) and 48 conventional pigs (96%). The number of E. coli per gram of colon content were significantly higher (6.81 log10UFC/g) than for organic pigs (6.19 log10UFC/g) (p=0.0033). A significant difference for the number of TET+E.coli per gram of colon content was also observed between organic (5.68 log10UFC/g) and conventional pigs (6.33 log10UFC/g) (p=0.00021). The level of tetracycline resistance is significantly (p=0.0033) higher for conventional pigs (57.4%) than for organic pigs (37.9%). A total of 374 E. coli and TET+E.coli isolates were collected. After typing by PFGE using XbaI enzyme, isolates were distributed in 275 pulsotypes. No pulsotype was common between organic and conventional. The diversity is very high, ID=0.997. Inside each production, only 2 pulsotypes was common between two herds. PFGE profiles didn’t permit to associate strains to their origin