Mo1766 Short Chain Fatty Acids and Bile Salts Modulate the Growth of Crohn's-Associated Adherent and InvasiveE. coli(AIEC)

in RNA polymerase (the bacterial target for rifaximin ) and E. coli phylogroup (A,B1,B2,D), evaluated by sequencing a1027 bp fragment of rpoB and triplex PCR respectively.RESULTS: Resistance to rifaximin was present in E. coli from 9/29 patients with IBD (7/24 CD, 2/5 UC) and correlated with prior rifaximin use (P<0.0001:CD, 6/8 treated vs 1/16 untreated; UC 2/2 treated vs 0/3 untreated).All rifaximin resistant strains were highly resistant (MIC = 1024 μg/ml, threshold value = 32 μg /ml).E. coli phylogroup was not associated with resistance.Mutations in rpoB were identified in 8/10 rifaximin-resistant strains vs 0/17 sensitive strains (P<0.0001).Mutations in rpoB were encoded by single amino acid substitutions: D516N (2 strains), H526N (3 strains), H526L (1 strain), N518D (1 strain), S574F (1 strain), previously described In Vitro.CONCLUSION: E. coli isolated from 31% of 29 patients with IBD exhibited high level resistance to rifaximin.The presence of resistance was strongly associated with prior use of rifaximin and amino acid substitutions in rpoB.These findings indicate that E. coli associated with IBD are commonly resistant to rifaximin and have significant implications for treatment trials targeting IBD-associated E. coli.