Effect of in-water administration of quorum system inhibitors in broilers' productive performance and intestinal microbiome in a mild necrotic enteritis challenge.

The poultry industry has been facing the impact of necrotic enteritis (NE), a disease caused by the bacterium Clostridium perfringens producing the haemolytic toxin NetB. NE severity may vary from mild clinical to prominent enteric signs causing reduced growth rates and affecting feed conversion ratio. NetB production is controlled by the Agr-like quorum-sensing (QS) system, which coordinates virulence gene expression in response to bacterial cell density. In this study, the peptide-containing cell-free spent media (CFSM) from Enterococcus faecium was tested in NE challenged broilers in two battery cage and one floor pen studies. Results showed a significant reduction of NE mortality. Metagenomic sequencing of the jejunum microbiome revealed no impact of the CFSM on the microbial community, and growth of C. perfringens was unaffected by CFSM in vitro. The expression of QS-controlled virulence genes netB, plc and pfoA was found to be significantly repressed by CFSM during the mid-logarithmic stage of C. perfringens growth and this corresponded with a significant decrease in haemolytic activity. Purified fractions of CFSM containing bioactive peptides were found to cause reduced haemolysis. These results showed that bioactive peptides reduce NE mortality in broilers by interfering with the QS system of C. perfringens and reducing bacterial virulence. Furthermore, the microbiome of C. perfringens-challenged broilers is not affected by quorum sensing inhibitor containing CFSM.

Overexpression of hns in the plant growth-promoting bacterium Enterobacter cloacae UW5 increases root colonization.

AIMS: Plant growth-promoting rhizobacteria (PGPR) introduced into soil often do not compete effectively with indigenous micro-organisms for plant colonization. The aim of this study was to identify novel genes that are important for root colonization by the PGPR Enterobacter cloacae UW5. METHODS AND RESULTS: A library of transposon mutants of Ent. cloacae UW5 was screened for mutants with altered ability to colonize canola roots using a thermal asymmetric interlaced (TAIL)-PCR-based approach. A PCR fragment from one mutant was reproducibly amplified at greater levels from genomic DNA extracted from mutant pools recovered from seedling roots 6 days after seed inoculation compared to that from the cognate inoculum cultures. Competition assays confirmed that the purified mutant designated Ent. cloacae J28 outcompetes the wild-type strain on roots but not in liquid cultures. In Ent. cloacae J28, the transposon is inserted upstream of the hns gene. Quantitative RT-PCR showed that transposon insertion increased expression of hns on roots. CONCLUSIONS: These results indicate that increased expression of hns in Ent. cloacae enhances competitive colonization of roots. SIGNIFICANCE AND IMPACT OF THE STUDY: A better understanding of the genes involved in plant colonization will contribute to the development of PGPR that can compete more effectively in agricultural soils.