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INTRODUCTION: ESBL-producing E. coli have become abundant all over the world and especially clonal lineages like ST131 and ST648 are of utmost importance. This study investigated the influence of ESBL-plasmids on non-resistance factors like biofilm formation, competition with commensals, competitive adhesion, serum resistance and motility of the host bacteria.
MATERIAL AND METHODS: Seven triplets of ESBL-carrying wild-type (WT) strains, their corresponding ESBL-plasmid-“cured” variant (PCV) and a complementary ESBLcarrying transformant (T) where analyzed in long-term colony, competition assays with commensals in co-cultures, competitive adhesion on IPEC-J2 cell lines, serum resistance, swimming motility, Biolog phenotypic microarrays, whole-genome sequence and RNA-sequence analysis.
For some of the triplets we detected enhanced curli and/or cellulose production and a reduced swimming capacity of the WT and T strain compared to their PCV. RNA sequencing revealed the chromosomally-encoded csgD-pathway as a key factor involved. Biolog results pointed towards a similar metabolic behavior of WT, PCV and T. In addition, ESBL plasmids played protective role against serum bactericidal activity and did not no generally present a burden to the host in competition assays against commensal E. coli in co-cultures and adhesion assays on epithelial cell lines. For some of the strains carriage of ESBL-plasmids was even advantageous for competition.
Our phenotypic and RNA sequencing results clearly indicate an influence of ESBLplasmids on non-resistance factors important for virulence and survival of the pathogenic strains, presumably contributing to their pandemic success.