Evaluation of a lytic bacteriophage, Φ st1, for biocontrol of Salmonella enterica serovar Typhimurium in chickens

Abstract

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.

Prevention of bacterial foodborne disease using nanobiotechnology

“…Bardina et al63 were able to reduce concentrations of Salmonella in chicken ceca by 4.4 log 10 CFU/g in 2 days and up to 2 log 10 CFU/g, compared with controls, at 8 days (end of experiment) following oral administration of phages. In a similar trial, Wong et al64 achieved a 2.9 log 10 CFU/mL reduction in bacterial concentrations after 6 hours, with Salmonella becoming undetectable in the cecum at 24 hours. A novel approach taken by Waseh et al65 was to purify the receptor (tail-spike) protein from a phage and feed it to chickens, attaining a 1–2 log 10 CFU/mL reduction in Salmonella concentration in chicken ceca.…”

Bacteriophages and their applications

“…In some cases, PEG precipitation is applied in the concentration of phage particles procedure. It was used to prepare high titers of Salmonella-specific phages by Bao et al (2011), Wong et al (2014, Bao et al (2015) and other researchers.…”

“…Centrifugation in CsCl gradients is ideal for purifying large amounts of phage, where the contaminant like bacterial lipopolysaccharide (i.e. endotoxin) can be removed from the phage preparations, resulting highly purified yields (Carlson, 2005 Bacillus cereus phage JBP901 (Shin et al, 2011), Salmonella enterica serovar Typhimurium phage Φst1 (Wong et al, 2014) and Staphylococcus aureus phage SPW .…”

“…On the contrary, a lower MOI ratio of 0.0001 was reported for bacteriophage AB1 of Acinetobacter baumannii (Yang et al, 2010). Recently, higher ratio of 0.1 was considered as the optimal MOI for Escherichia phage CICC 80001 (Xu et al, 2016) and Salmonella Typhimurium phage Φst1 (Wong et al, 2014). Meanwhile, the proliferation rate of bacteriophages always depends on their latent period and burst size along with the number of infected cells.…”

“…Reports showed that the viability of bacteriophages is greatly affected by temperature (Yang et al, 2010;Baudoux et al, 2012;Kęsik-Szeloch et al, 2013;Wong et al, 2014), which specifically influencing in their attachment, penetration, multiplication, and the length of the latent period (Jończyk et al, 2011). Most bacteriophages act optimally at temperatures between 30 -50˚C (Bao et al, 2015;Ji et al, 2015;Zhang et al, 2015).…”