Molecular Microbiology Research 2024, Vol.14, No.1, 1-9 http://microbescipublisher.com/index.php/mmr 6 SPI-2. These proteins help Salmonella evade the attack of the host immune system while also acquiring necessary nutrients and growth conditions within the host cell. In addition to invading the host cell interior, Salmonella can also interact with host cells in other ways. For example, Salmonella can release toxins that disrupt the structure and function of host cells. These toxins include endotoxins, cytotoxins, and hemolysins. These toxins can cause the death of host cells and tissue damage, the 3.2 The impact of Salmonella on the host immune system After Salmonella infection, the host immune system initiates a series of immune responses, such as the inflammatory response and adaptive immune response mentioned earlier. However, Salmonella can also influence the host immune system in various ways to promote its growth and reproduction. Salmonella first alters the balance of the host immune system. It can release specific molecules that act as inflammatory cytokines and cause inflammation and tissue damage. Additionally, Salmonella can suppress certain components of the host immune system, such as T cells and macrophages, reducing the host's ability to fight the infection. Salmonella also interferes with signal transduction in the host immune system. For example, Salmonella can release proteins such as SipA and SopB through its T3SS to alter signal transduction pathways in host cells. These proteins can interfere with key molecules in cell signaling pathways, such as Rho GTPase, thereby affecting the biological behavior of host cells. Salmonella also exploits the host immune system to promote its own growth and reproduction. For instance, Salmonella can regulate the host immune response by releasing molecules such as flagellin and bile acids. Bile acids are compounds found in bile that are released by Salmonella upon infection. Flagellin stimulates the production of bile acids by host intestinal epithelial cells. Bile acids can interact with the host's TGR5 receptor to inhibit the inflammatory response of immune cells, thereby helping Salmonella evade the host's immune attack (Flynn and Chan, 2003; Raffatellu et al., 2006). 3.3 The immune evasion mechanisms of Salmonella against immune responses Salmonella can evade the attack of the host immune system through various mechanisms. For example, Salmonella can alter its surface structure to avoid recognition and attack by the host immune system. Salmonella can change the structure of its LPS molecules to evade antibodies and immune cells produced by the host immune system. Salmonella also releases molecules that interfere with the function of the host immune system. These proteins can affect the biological behavior of host cells, making it difficult for them to effectively fight Salmonella infections. Salmonella can also use its T3SS to evade the attack of the host immune system. The T3SS injects Salmonella proteins directly into host cells, altering their biological activity. These proteins can help Salmonella evade the attack of the host immune system while also acquiring necessary nutrients and growth conditions within the host cell (Arciola et al., 2018). Salmonella can also interfere with the balance of the host immune system. Salmonella can activate the host immune system by releasing specific molecules, such as LPS and flagellin. These molecules stimulate the production of large amounts of inflammatory cytokines, such as TNF-α, IL-1β, IL-6, etc. (Bueno et al., 2007). These inflammatory cytokines cause inflammation and tissue damage, weakening the host's ability to fight the infection and providing a better growth environment for Salmonella. 4 Diagnosis and Treatment of Salmonella Infection 4.1 Diagnostic methods for Salmonella infection The diagnosis of Salmonella infection is achieved by isolating and identifying Salmonella. Traditional diagnostic methods include cultivation and biochemical analysis. In these methods, samples are usually collected from biological fluids such as blood, feces, urine, etc. of patients. After processing, the samples are cultured and biochemically analyzed to detect the presence of Salmonella. The advantages of these methods are simplicity and ease of operation, but they require a relatively long time and usually take several days to obtain results.
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