The diversity of the Escherichia coli species is in part due to the large number of mobile genetic elements that are exchanged between strains. We report here the identification of a new integrative and conjugative element (ICE) of the pKLC102/PAGI-2 family located downstream of the tRNA gene pheU in the E. coli strain BEN374. Indeed, this new region, which we called ICEEc2, can be transferred by conjugation from strain BEN374 to the E. coli strain C600. We were also able to transfer this region into a Salmonella enterica serovar Typhimurium strain and into a Yersinia pseudotuberculosis strain. This transfer was then followed by the integration of ICEEc2 into the host chromosome downstream of a phe tRNA gene. Our data indicated that this transfer involved a set of three genes encoding DNA mobility enzymes and a type IV pilus encoded by genes present on ICEEc2. Given the wide distribution of members of this family, these mobile genetic elements are likely to play an important role in the diversification of bacteria.
Coccidiosis is a widespread intestinal disease of poultry caused by a parasite of the genus Eimeria. Eimeria tenella, is one of the most virulent species that specifically colonizes the caeca, an organ which harbors a rich and complex microbiota. Our objective was to study the impact of the intestinal microbiota on parasite infection and development using an original model of germ-free broilers. We observed that germ-free chickens presented significantly much lower load of oocysts in caecal contents than conventional chickens. This decrease in parasite load was measurable in caecal tissue by RT-qPCR at early time points. Histological analysis revealed the presence of much less first (day 2pi) and second generation schizonts (day 3.5pi) in germ-free chickens than conventional chickens. Indeed, at day 3.5pi, second generation schizonts were respectively immature only in germ-free chickens suggesting a lengthening of the asexual phase of the parasite in the absence of microbiota. Accordingly to the consequence of this lengthening, a delay in specific gamete gene expressions, and a reduction of gamete detection by histological analysis in caeca of germ-free chickens were observed. These differences in parasite load might result from an initial reduction of the excystation efficiency of the parasite in the gut of germ-free chickens. However, as bile salts involved in the excystation step led to an even higher excystation efficiency in germ-free compared to conventional chickens, this result could not explain the difference in parasite load. Interestingly, when we shunted the excystation step in vivo by infecting chickens with sporozoites using the cloacal route of inoculation, parasite invasion was similar in germ-free and in conventional chickens but still resulted in significantly lower parasite load in germ-free chickens at day 7pi. Overall, these data highlighted that the absence of intestinal microbiota alters E. tenella replication. Strategies to modulate the microbiota and/or its metabolites could therefore be an alternative approach to limit the negative impact of coccidiosis in poultry.
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