2. Universidad Cardenal Herrera-CEU

New measures applied to reduce antimicrobial resistances (AMR) at field level in broiler production are focused on improving animals’ welfare and resilience. However, it is necessary to have better knowledge of AMR epidemiology. Thus, the aim of this study was to evaluate AMR and multidrug resistance (MDR) dynamics during the rearing of broilers under commercial (33 kg/m2 density and max. 20 ppm ammonia) and improved (17 kg/m2 density and max. 10 ppm ammonia) farm conditions. Day-old chicks were housed in two poultry houses (commercial vs. improved), and no antimicrobial agents were administered at any point. Animals were sampled at arrival day, mid-period and at slaughter day. High AMR rates were observed throughout rearing. No statistical differences were observed between groups. Moreover, both groups presented high MDR at slaughter day. These results could be explained by vertical or horizontal resistance acquisition. In conclusion, AMR and MDR are present throughout rearing. Moreover, although a lower level of MDR was observed at mid-period in animals reared under less intensive conditions, no differences were found at the end. In order to reduce the presence of AMR bacteria in poultry, further studies are needed to better understand AMR acquisition and prevalence in differing broiler growing conditions.

Phage-inducible chromosomal islands (PICIs) represent a novel and universal class of mobile genetic elements, which have broad impact on bacterial virulence. In spite of their relevance, how the Gramnegative PICIs hijack the phage machinery for their own specific packaging and how they block phage reproduction remains to be determined. Using genetic and structural analyses, we solve the mystery here by showing that the Gram-negative PICIs encode a protein that simultaneously performs these processes. This protein, which we have named Rpp (for redirecting phage packaging), interacts with the phage terminase small subunit, forming a heterocomplex. This complex is unable to recognize the phage DNA, blocking phage packaging, but specifically binds to the PICI genome, promoting PICI packaging. Our studies reveal the mechanism of action that allows PICI dissemination in nature, introducing a new paradigm in the understanding of the biology of pathogenicity islands and therefore of bacterial pathogen evolution.

Phage-inducible chromosomal islands (PICIs) are a recently discovered family of pathogenicity islands that contribute substantively to horizontal gene transfer, host adaptation and virulence in Gram-positive cocci. Here we report that similar elements also occur widely in Gram-negative bacteria. As with the PICIs from Gram-positive cocci, their uniqueness is defined by a constellation of features: unique and specific attachment sites, exclusive PICI genes, a phage-dependent mechanism of induction, conserved replication origin organization, convergent mechanisms of phage interference, and specific packaging of PICI DNA into phage-like infectious particles, resulting in very high transfer frequencies. We suggest that the PICIs represent two or more distinct lineages, have spread widely throughout the bacterial world, and have diverged much more slowly than their host organisms or their prophage cousins. Overall, these findings represent the discovery of a universal class of mobile genetic elements.