Invasion of avian reproductive tissues by Salmonella typhimurium and Salmonella enteritidis
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In recent decades salmonellosis has been on the rise as a food related illness worldwide. Causing over 24% of all non-typhoidal Salmonellosis cases, SE is the most frequently isolated serovar of Salmonella. Increased isolation of SE from eggs has paralleled an increase in the number of transovarian infections associated with laying hens in the poultry industry. This route of infection is a fairly new line of study when compared to the more traditional path where SE originates from fecal contamination through the shell. Salmonella Typhimurium (ST) is another concern for the egg industry. ST has caused 23.5% of all non-typhoidal salmonellosis cases. Understanding these two egg pathogens requires an in depth look at the mechanisms by which an egg may support infection and bacterial growth. Eggs were inoculated with both SE and ST onto the vitelline membrane and incubated for 24 hours. It was hoped that by gathering samples from the interior of the egg membrane, the albumen of the egg, and the membrane itself, some clarification as to when Salmonella is allowed to grow within the egg could be gathered. Albumen and membrane were found to be more hospitable environments to bacterial growth with increased storage times. In order to better understand the movement of bacteria into pre-ovulatory tissues, samples were gathered from mature laying hens. Follicular tissues were separated into divisions based on maturity, and bacteria were added to an in vitro cell culture broth containing the follicles. The point of this experiment was to determine if either species of Salmonella preferentially moved into follicles of different maturity when inoculated in vitro. A third experiment looked into the role of developmental stages of the vitelline membrane in exclusion of bacteria from the nutrient rich yolk. Tissues were gathered in the method described above. The follicular sack was removed from half of these samples and left intact for the other half. Another treatment group included was the yolks of eggs which had been laid by the same flock of birds. Results showed that follicles with intact follicular sacks were more susceptible to bacterial colonization than other treatment groups.
Howard, Zoe R. (2003). Invasion of avian reproductive tissues by Salmonella typhimurium and Salmonella enteritidis. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from