Effects of heterophil adaptation on Salmonella enteritidis fecal shedding and egg contamination

Serial passage of wild-type Salmonella enteritidis (SE) in chicken heterophils resulted in decreased shedding of SE in chicken feces and reduced egg contamination. When serially heterophil-passaged strains (heterophil-adapted SE [HASE]) were given to groups of 12 or more laying hens in drinking water at a dose of 10(8) colony-forming units for 3 consecutive days, the inoculum persisted in the feces at low frequency for a few days only. Two challenge wild-type strains, given in similar manner, persisted in feces at high frequency for 25 days or longer. The persistence of challenge strains in hens previously exposed to HASE was considerably shorter and occurred less frequently than persistence and frequency in challenge control hens. HASE strains were not isolated from any of 494 eggs laid after exposure to HASE. The challenge strain was isolated from 15 of 208 eggs (7.2%) after challenge of control hens and never from 461 eggs laid after challenge of "vaccinated" hens. I concluded that HASE clones obtained by five or more cycles of heterophil phagocytosis were avirulent and immunogenic.