Bioinformatic analyses of a potential Salmonella-virus-FelixO1 biocontrol phage BPS15S6 and the characterisation and anti-Enterobacteriaceae-pathogen activity of its endolysin LyS15S6
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Foodborne Enterobacteriaceae pathogens, especially Salmonella, still seriously threaten food safety. To establish a foundation for further developing phage- and endolysin-based methods combating these pathogens, in this study, the newly isolated Salmonella-virus-FelixO1 phage BPS15S6 for biocontrol purposes was characterised by genomic bioinformatic analysis, and then its endolysin LyS15S6 was obtained using a prokaryotic expression system, characterised in vitro and evaluated in the antibacterial efficacy. It was shown that BPS15S6 had an 87,609-bp genome with 130 open reading frames and does not appear to carry known lysogeny-associated genes and other damaging genetic determinants and is unlikely to perform generalised transduction. Furthermore, LyS15S6 was determined to possess the high enzymatic activity of 1,001,000 U mg−1 and the broad spectrum of lysing 56 tested Gram-negative strains. The assays of thermostability and optimum pH revealed that LyS15S6 was stable up to 40 °C and more active at pH 7. Notably, we demonstrate that edible ε-poly-l-lysine (EPL) can be used as an outer-membrane permeabiliser to improve the antibacterial performance of endolysins. When combined with 1 μg ml−1 EPL, 2 μM LyS15S6 could cause 3–4 log viable cell reductions of the three tested Enterobacteriaceae pathogens in vitro after 2 h of reaction at 25 °C and 2.56 and 3.14 log reductions of Salmonella ATCC13076 after 15 min of reaction at 25 °C and 2 h of reaction at 8 °C respectively. A new strategy, the combined application of endolysins and edible EPL for combating Enterobacteriaceae pathogens in food, is thus presented in this work.
KeywordsGram-negative bacteria Genome Glycoside hydrolase Epsilon-poly-l-lysine Outer membrane permeabiliser
We are grateful to Prof. Baowei Yang (Northwest A&F University, China) and Dr. Hongduo Bao (Jiangsu Academy of Agricultural Sciences, China) for generously providing bacterial strains. This work was supported by the Young Scientific Talents Foundation of Guizhou Provincial Education Department [Grant Number KY(2017)211].
HH conceived and designed this study, performed a major part of experiments, analysed the data and wrote this manuscript. XL isolated the phages and performed mainly the assays of phages EOP and antibacterial activity of the endolysin. TZ was involved in the design of this study, the bioinformatic analyses, the peptidoglycan hydrolysis test and the determination of endolysin lytic spectrum. XW was involved in the overexpression, purification, detection and quantitative determination of the endolysin. JZ, CZ, HT, YZ and BC were involved in the assays of endolysin antibacterial activity. RW was involved in the data analysis and the revise of this manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interests.
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