Stressors may influence chicken susceptibility to pathogens such as Salmonella enterica. Feed withdrawal stress can cause changes in normal intestinal epithelial structure and may lead to increased attachment and colonization of Salmonella. This study aimed to investigate modulatory effects of epigenetic modification by feed restriction on S. enterica serovar Enteritidis colonization in broiler chickens subjected to feed withdrawal stress. Chicks were divided into four groups: ad libitum feeding; ad libitum feeding with 24-h feed withdrawal on day 42; 60% feed restriction on days 4, 5, and 6; and 60% feed restriction on days 4, 5, and 6 with 24-h feed withdrawal on day 42. Attachment of S. Enteritidis to ileal tissue was determined using an ex vivo ileal loop assay, and heat shock protein 70 (Hsp70) expression was evaluated using sodium dodecyl sulphate-polyacrylamide gel electrophoresis and western blotting. Feed withdrawal stress increased S. Enteritidis attachment to ileal tissue. However, following feed withdrawal the epigenetically modified chickens had significantly lower attachment of S. Enteritidis than their control counterparts. A similar trend with a very positive correlation was observed for Hsp70 expression. It appears that epigenetic modification can enhance resistance to S. Enteritidis colonization later in life in chickens under stress conditions. The underlying mechanism could be associated with the lower Hsp70 expression in the epigenetically modified chickens.
In this study, a Salmonella Typhimurium lytic bacteriophage, Φ st1, which was isolated from chicken faecal material, was evaluated as a candidate for biocontrol of Salmonella in chickens. The morphology of Φ st1 showed strong resemblance to members of the Siphoviridae family. Φ st1 was observed to be a DNA phage with an estimated genome size of 121 kbp. It was found to be able to infect S. Typhimurium and S. Hadar, with a stronger lytic activity against the former. Subsequent characterisation of Φ st1 against S. Typhimurium showed that Φ st1 has a latent period of 40 min with an average burst size of 22 particles per infective centre. Approximately 86.1% of the phage adsorbed to the host cells within the initial 5 min of infection. At the optimum multiplicity of infection (MOI) (0.1), the highest reduction rate of S. Typhimurium (6.6 log₁₀ CFU/ml) and increment in phage titre (3.8 log₁₀ PFU/ml) was observed. Φ st1 produced adsorption rates of 88.4-92.2% at pH7-9 and demonstrated the highest bacteria reduction (6.6 log₁₀ CFU/ml) at pH9. Φ st1 also showed an insignificant different (P>0.05) reduction rate of host cells at 37 °C (6.4 log₁₀ CFU/ml) and 42 °C (6.0 log₁₀ CFU/ml). The in vivo study using Φ st1 showed that intracloacal inoculation of ~10¹² PFU/ml of the phage in the chickens challenged with ~10¹⁰ CFU/ml of S. Typhimurium was able to reduce (P<0.05) the S. Typhimurium more rapidly than the untreated group. The Salmonella count reduced to 2.9 log₁₀ CFU/ml within 6h of post-challenge and S. Typhimurium was not detected at and after 24h of post-challenge. Reduction of Salmonella count in visceral organs was also observed at 6h post-challenge. Approximately 1.6 log₁₀ FU/ml Φ st1 was found to persist in the caecal wall of the chicks at 72 h of post-challenge. The present study indicated that Φ st1 may serve as a potential biocontrol agent to reduce the Salmonella count in caecal content of chickens.