Location of Salmonella typhimurium during incubation and hatching of inoculated eggs.

Location of Salmonella during hatching of broiler chicks was studied in three experiments. Unincubated, fertile hatching eggs heated to 42 C were inoculated by immersion for 15 min in a 16 C physiological saline solution containing approximately 1 x 10(5) cfu/mL of a nalidixic acid-resistant strain of Salmonella typhimurium. All eggs were sanitized externally by wiping with a paper towel wet with 70% ethanol. When incubating eggs were transferred to a hatcher, each was placed in a closed paper bag to minimize cross-contamination. Unhatched eggs were sampled by cutting away the shell over the air cell, sanitizing the inner air cell membrane with 70% ethanol, and removing the contents through the membrane. Shells and membranes were crushed and mixed in 10 mL buffered peptone (BP). Yolks were dissected out, dipped in 70% ethanol, and mixed with 10 mL BP. Embryos or chicks and all surrounding fluid were rinsed in 100 mL BP. A total of 172 eggs was sampled. Shells and membranes were 100% Salmonella-positive 30 min after inoculation, but only 38% were positive after 17 to 21 days of incubation. No chick rinses were positive before pipping, but 15% were positive after pipping. Yolk samples were 2% positive before pipping versus 8% after pipping. A majority of chicks hatching from positive shells and membranes were Salmonella-negative.