Poultry meat is the most common protein source of animal origin for humans. However, intensive breeding of animals in confined spaces has led to poultry colonisation by microbiota with a zoonotic potential or encoding antibiotic resistances. In this study we were therefore interested in the prevalence of selected antibiotic resistance genes and microbiota composition in feces of egg laying hens and broilers originating from 4 different Central European countries determined by real-time PCR and 16S rRNA gene pyrosequencing, respectively. strA gene was present in 1 out of 10,000 bacteria. The prevalence of sul1, sul2 and tet(B) in poultry microbiota was approx. 6 times lower than that of the strA gene. tet(A) and cat were the least prevalent being present in around 3 out of 10,000,000 bacteria forming fecal microbiome. The core chicken fecal microbiota was formed by 26 different families. Rather unexpectedly, representatives of Desulfovibrionaceae and Campylobacteraceae, both capable of hydrogen utilisation in complex microbial communities, belonged among core microbiota families. Understanding the roles of individual population members in the total metabolism of the complex community may allow for interventions which might result in the replacement of Campylobacteraceae with Desulfovibrionaceae and a reduction of Campylobacter colonisation in broilers, carcasses, and consequently poultry meat products.

1Salmonella Infantis (SI) became endemic in Hungary where the PFGE cluster B, 2 characterized by a large multiresistance (MDR) plasmid emerged among broilers leading to 3 an increased occurrence in humans. We hypothesised that this plasmid (pSI54/04) assisted 4 dissemination of SI. Indeed, Nal-Sul-Tet phenotypes carrying pSI54/04 occurred increasingly 5 between 2011-2013 among SI isolates from broilers and humans. Characterization of 6 pSI54/04 based on genome sequence data of the MDR strain SI54/04 indicated a size of ~277 7 kb and a high sequence similarity with the megaplasmid pESI of SI predominant in Israel. 8Molecular characterization of 78 representative broiler and human isolates detected the 9 prototype plasmid pSI54/04 and its variants of together with novel plasmid associations 10 within the emerging cluster B. To test in vitro and in vivo pathogenicity of pSI54/04 we 11 produced plasmidic transconjugant of the plasmid-free pre-emergent strain SI69/94. This 12 parental strain and its transconjugant have been tested on chicken embryo fibroblasts (CEFs) 13 and in orally infected day old chicks. The uptake of pSI54/04 did not increase the 14 pathogenicity of the strain SI69/94 in these systems. Thus, dissemination of SI in poultry 15 could be assisted by antimicrobial resistance rather than by virulence modules of the endemic 16 plasmid pSI54/04 in Hungary. 17