Methods for inoculation and recovery of Salmonella from chicken eggs

Various methods of applying inoculum and recovering low numbers of artificially inoculated Salmonella typhimurium on eggs were evaluated. Inoculation methods tested were suspending cells in 1) .85% saline; 2) 1% peptone; 3) sterile chicken fecal paste; or 4) a 1:10 dilution of chicken feces in .85% saline. Sampling methods tested were 1) shell and membrane massage; and 2) mortar and pestle grinding of shells and membranes. The method that yielded the best recovery of low numbers of Salmonella was as follows: 1) apply cell suspension in 1% peptone to egg; 2) sample egg by a hand crush and massage of shell and membranes in 50 mL of buffered peptone; 3) incubate shell and membranes in buffered peptone overnight and then plate onto selective agar. Methods that did not improve sensitivity of recovery included varying the inoculum drying time, addition of FeSO4 or Cleland's reagent to the recovery medium, and varying the temperature of the inoculum to affect penetration.