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.