Translocation of Orally Inoculated Salmonella Following Mild Immunosuppression via Dexamethasone Infusions in Dairy Steers and the Presence of the Salmonella in Atypical Anatomical Locations.
Type of DegreeMaster's Thesis
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Salmonella is a foodborne pathogen of increasing concern in the U.S. as foodborne and legislative action against foods containing this pathogen is being developed. Salmonella is the leading bacteria associated with foodborne illness in the U.S. (CDC, 2018). The objective of this study was to determine if immunosuppression via daily dexamethasone (DEX) infusion altered Salmonella Typhimurium (SAL) translocation from the GI tract to atypical locations. Weaned Holstein steer calves (n = 20; BW = 102 ± 2.7kg) received DEX (n = 10; 0.5mg/kg BW) or saline (CON; n = 10; 0.5mg/kg BW) for 4 d (from d -1 to d 2) prior to oral inoculation of SAL (3.4 x 106 CFU/animal) via milk replacer on d 0. Fecal swabs for SAL shedding were obtained daily and samples were confirmed positive beginning 24 h post inoculation (d 1) to harvest (d 5). Dexamethasone administration was achieved via indwelling jugular catheters fitted simultaneously with rectal temperature (RT) recording devices on d −2 relative to inoculation and placed in individual pens in an environmentally controlled facility. Whole blood was collected at -24, -12, and 0 h; and 8-h intervals from 8 to 120 h for hematology. Upon harvest (d 5), the ileum, cecal content, lymph nodes (ileocecal, mandibular, popliteal, and prescapular), and synovial (stifle, coxofemoral and shoulder) swabs were collected for the isolation of the inoculated strain of SAL. Following inoculation, 100% of DEX calves shed the experimental strain of SAL for 5 d, 90% of CON calves shed from d 1 to 3, and 100% of CON calves shed from d 4 to 5. There was a time x treatment (P < 0.01) for RT such that the DEX treatment resulted in a decreased RT on d -1 to 2. There were increased WBC and neutrophils in DEX steers (P < 0.0001), and lymphocytes increased following DEX administration (P = 0.02 at 24 and 48h, respectively. Greater (P < 0.01) concentrations of SAL were quantified from the cecum of DEX calves (3.86 ± 0.37 log CFU) than CON (1.37 ± 0.37 log CFU); There was no difference in SAL concentrations between DEX and CON calves in ileal tissue (P = 0.07), nor ileocecal (P = 0.57), mandibular (P =0.12), popliteal (P = 0.99), nor prescapular (P = 0.83) lymph nodes. Salmonella was isolated from the stifle joint of one calf in the CON group; however, SAL was not isolated from any other joint fluids sampled. Of the stifle samples collected, 3.3% were positive for SAL indicating the opportunity of contaminating the meat during hind quarter fabrication. These data may be interpreted as either a mild immunosuppression due to multiple DEX exposures, or a combination of both mild immunosuppression and slight return of immune function when juxtaposing DEX with Salmonella inoculation. While more research is needed to elucidate the interactions of immunosuppression and pathogen migration patterns, these data confirm that orally inoculated SAL can translocate from the G.I. and be harbored in atypical locations representing a food safety risk.