Prevalence And Characteristics Of Salmonella In Large-Scale Chicken Farms And Evaluation Of Phage Disinfectants As New Biological Measures

According to WHO records,Salmonella spp.is a main pathogen that endangers food safety worldwide.Chickens and their products contaminated with Salmonella are one of the major sources of human salmonellosis.China is a large producer and consumer for poultry and poultry products,and it needs pay more attentions.However,during chickens raising,many food-borne zoonotic Salmonella serovars are latent infections and are easily overlooked.In current,large-scale breeding farms are main source of poultry production and also a source of Salmonella transmission.Healthy breeding farms of chicken can guarantee safety downstream production,which can ensure healthy food supply from farm to fork in China.In this study,Salmonella survey was conducted in three large-scale chicken farms in China,in order to reveal Salmonella prevalence in large-scale chicken farms,and to defermine key points of Salmonella transmission and to evaluate phage disinfectants as new biological measures.1 Prevalence and characteristics of Salmonella in large-scale chicken farmsAt first,Salmonella sero-epidemiological survey was performed,780 serum samples from three different breeder farms in were detected.The positive rate of Salmonella infection in A farm was 5.30%,B farm was 16.72%,and C farms was 11.57%.And then,Salmonella etiology was carried out.539 Salmonella strains were isolated from 2,033 samples.Among them,518 isolates were identified as Salmonella Enteritidis(SE)(96.10%),the remains are other serovars(3.90%)Antimicrobial resistance results showed that the rate of nalidixic acid resistance was highest(99.13%),followed by nitrofurantoin(72.60%)and ampicillin(62.60%);the resistance rate of streptomycin was 62.17%and the enrofloxacin was 44.78%,amoxicillin was 36.08%.The drug-resistance of other detected antibitics was below 8.26%120 out of reandom 122 SE isolates from 3 farms were consistant,all of 6 virulence genes were positant.CRISPR results showed that all detected isolates were SET1 type,which was same with P1251209.WGS results showed that they belonged to a same clonal cluster because their similarity was 99.80-100.00%.These results showed that this kind of SE isolates might be a same endemic strain on these farms.To find critical points of Salmonella transmission,57 SE isolates from one farm were analyzed,using PFGE technigue.The results showed that the SE isolates in this chicken farm were mainly derived from drink water and environment,and clarified that drink water and environment were possible major sources of transmission.2 Evaluation of phage disinfectants as new biological measuresAfter drink water and environment were determined as the key points,Salmonella clearance measures were further explored.5 different types of chemical disinfectants were selected for measurement of their minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC).The results showed that five different types of disinfectants had good effects on Salmonella clearance,and MIC was 10.42 ?g/mL for Didecyl dimethyl ammonium bromide,250 ?g/mL for Compound Peroxymonealphate,and 500 ?g/mL for Dichloroisocyanurate,5,000?g/mL for Povidone Iodine,312.5 ?g/mL for Dilute Glutaral,31.25 ?g/mL for Glutaral and Deciquam,62.5 ?g/mL for Glutaral and Benzalkonium Bromide,and their MBC results were basically consistent with the MIC results,except for the Dilute Glutaral,which were changed from 312.5 ?g/mL to 625 ?g/mL.Furthermore,the effect of phages was evaluated as a novel Salmonella-specific biological disinfectant,and the results showed in vitro assary,phage LP31 could completely kill SE in water at 25? and 37?.SE on the ground environment could be killed by sprayed phage,SP55 and LP31 could be reduced SE at the level of 0.643 and 0.951 log CFU/mL,compared to the control group.And further in vivo assary with oral inoculation of phage LP31,SE in chicken body could be reduced significantly by oral phage LP31 at the level of 3.021 logCFU/mL,compared to the control group.In summary,we found that Salmonella infection are still serious in breeder poultry farms.SE was the dominant serotype.Drink water and environment are important key points in trainsmistion of Salmonella infection.Phage could be used as a new biological disinfectant to reduce Salmonella and block its propagation.