Investigation On The Contamination Of Drug-resistant Salmonella In Catering Food And Its Phage Ecological Control

Salmonella is a kind of food-borne zoonotic pathogen,which can directly or indirectly contaminate food,cause food poisoning,and cause great harm to food safety.The large abuse of antibiotics has led to the development of resistance and cross-resistance of Salmonella,making it difficult to control.Therefore,studying the contamination status of Salmonella in daily catering foods,drug resistance and phage ecological control strategies are of great significance for the control of Salmonella and keep food safety.First,a method based on polymerase chain reaction(PCR)was established to evaluate the contamination status of Salmonella in daily catering foods.A specific 284 bp specific DNA fragment was amplified using specific primers,and the minimum detection limit of Salmonella template DNA was 4 ng/L.The Salmonella contamination in 23 food samples collected by the market was evaluated by PCR and conventional methods.14 of them were detected by conventional methods,and 12 of them were detected by PCR.The average contamination rate of the food-selling Salmonella is high and needs to be paid attention to by consumers.Secondly,45 strains from the laboratory of Animal and Plant Food Testing Center of Jiangsu Entry-Exit Inspection and Quarantine Bureau were serotyped,and 21 strains of Salmonella were obtained by bacterial screening,identification and biochemical tests.The detection rate was 46.67%.At the same time,the resistance and drug resistance genes of 23 strains were studied.The results showed that there are 6,0,0,11,6,2,8 and 5 strains resistant ampicillin,amikacin,kanamycin,streptomycin,tetracycline,norfloxacin,cotrimoxazole,and chloramphenicol,respectively.The resistant strains can amplify related drug resistance genes.Finally,a strain of S.enterilidis was used as the host strain to study the effect of using phage to control it.A strong lytic phage was isolated and purified from chicken manure by double-layer plate agar method,named as SpapYZUOl,which was identified as phage phage virus by morphological identification.The host infection experiment showed that the multiplicity of MOI was 1,000,the progeny The titer was the highest;a one-step growth experiment showed that the incubation period of the infected host was 10 min,the lysis period was 90 min,and the average lysis amount was about 290.The genome sequencing results showed that the SpapYZUOI genome was 88,539 bp in length and GC content was 42.32%.There were 126 open reading frames(ORFs),of which 28 encoded known functional protein genes.The phage SpapYZU01 is less acquainted with known viral sequences and may be a new class of viruses.The phage has a significant inhibitory effect on the growth of S.enteritidis in both the medium and the pork.It has the potential to be formulated as a green biocontrol agent for S.enteritidis.