Pathogenicity analysis of Salmonella pullorum infection in laying hens
To understand the pathogenic characteristics of Salmonella pullorum-infected laying hens,liver and other tissues of infected hens from February to November 2022 were collected for the study.The livers of diseased chickens were isolated,and the isolates were identified by multi-plex PCR and serotyped;pathological sections were prepared from the diseased livers and other tis-sues to observe the pathological changes;the expression levels of virulence genes and cytokine mR-NA of Salmonella pullorum in liver and spleen tissues were analyzed by qRT-PCR.The results showed 18 strains of bacteria were isolated from the submitted laying hens,and small colorless col-onies grown on MacConkey medium,they were identified by multiplex PCR and serotyped as Sal-monella fowl dysentery;pathological sections showed infiltration of inflammatory cell clusters and cell necrosis in the myocardium,liver,and lungs.qRT-PCR assay showing upregulation of the ex-pression levels of virulence genes such as biofilm-related genes(CsgB,RpoS,bcsA and PagC),SPI-1 genes(HilA,InvA,PrgH and SipC)and SPI-2 genes(SteE,RcsC,SseL and SpiC)in-duced in sick chickens infected with Salmonella pullorum;the expression levels of IL-1β,IL-6,IL-4 and IL-13 were up-regulated and the expression levels of IL-18 and IFN-γ were decreased in the liver of infected laying hens;IL-6 was highly expressed and IL-1β and IL-18 expression levels were significantly decreased in the spleen.In this study,the expression of biofilm-related genes,SPI-1,SPI-2-related virulence genes and TH2-secreted cytokines was up-regulated in the tissues of infec-ted chickens,indicating that Salmonella pullorum invaded the host in different ways intracellularly and extracellularly,leading to its massive proliferation and dissemination,causing pathological changes and autoimmune responses.
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