| Salmonella is a ubiquitous bacterial pathogen for anthropozoonosis in nature,and it has been identified as the dominating cause of foodborne illness worldwide.With the long-term and large-scale use of antibiotics, antibiotic resistance rates havebeen increasing in various regions throughout the world, which makes it an urgentproblem to be solved. Bacteriophage has been widely applied to food safety byscientists, and it has showed great potential as the alternative biocontrol agents.Therefore, it is necessary to study on the safety assessement, production andapplication of bacteriophage. The main points and results of this work are shown asfollows with bacteriophage STP4-a as the research object.1. Safety analysis of bacteriophage STP4-a: In silico, the safety evaluation wasperformed by comparing all the open reading frames (ORFs) of bacteriophage STP4-athrough BLAST, and then protein sequences were compared through allergendatabase. In the acute toxicity test, the morbidity, mortality, and variation of weight,food and states of life were surveilled and recorded, and all animals were examinedfor gross pathology. The results revealed that none of the putative phage proteins hasany homologies to any phage lysogeny factors, toxins, pathogen-related genes orfoodborne allergens. A single-dose test of oral toxicity in mice revealed no morbidity,mortality or abnormal clinical observation, and no difference between thebacteriophage treatment groups and control groups on body weight, organ weight orother histopathology. In conclusion, bacteriophage is a relatively safe biocontrolagent.2. Optimization and production of bacteriophage STP4-a: In200mL liquidproliferation system, incubation time, temperature, pH and multiplication of infection (MOI) value were optimized, with Ca2+、Mg2+、Fe2+、Zn2+further enhancing theeffects. The optimization effects were determined by phage titer. Thereafter, theoptimal conditions were confirmed through5L fermentation system. Bacteriophagein liquid form was freeze-dried to powder for further storage, the activity of whichwas also estimated by phage titer. The results showed that the optimal conditions in200mL liquid proliferation system were determined as: incubation temperature37℃,rotation rate200r/min, ion concentration10mmol/L CaCl2in Nutrient Broth, MOIvalue10-5and incubated time10-12h. Then it has been indicated in5L fermentationsystem that control groups increased by3log (pfu/mL) after fermentation, whileoptimal groups increased by8log (pfu/mL), which makes it possible for the furtherindustrialized fermentation of bacteriophage. The storage experiment showed that itmade beneficial effects both on titer and appearance with10%skim milk as theprotective agent in freeze-drying process.3. Application of bacteriophage STP4-a for biocontrol of Salmonella in chicken:The potential of the application of bacteriophage STP4-a was performed through lyticspectrum and the effects of therapy. The results revealed that bacteriophage STP4-awas lytic to10Salmonella isolated from poultry, while non-Salmonella species wereresistant to bacteriophage STP4-a. It can be inferred that bacteriophage STP4-a is abroad-spectrum bacteriophage lytic to Salmonella specifically. In the therapyexperiment, the layer chicken were oral administrated with107cfu Salmonella; twoweeks later, the counts of Salmonella in the intestines of bacteriophage treatmentgroups decreased by one log (cfu/g) significantly (P<0.05) compared with controlgroups. In general, bacteriophage STP4-a has showed a positive prospect inapplication on livestock and poultry, food or medicine areas. |
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