Experimental horizontal transmission of Salmonella enteritidis strains (phage types 4, 8, and 13a) in chicks

The recent isolation of phage type 4 Salmonella enteritidis strains from poultry and humans in the United States has generated considerable concern because this phage type is predominant in both animals and humans in many other nations. Understanding whether the presence of these strains in poultry flocks poses an elevated threat to public health is a critical issue for developing effective disease control programs. The present study evaluated whether S. enteritidis strains of various phage types found in poultry in the United States (phage types 4, 8, and 13a) differed in their potential for horizontal transmission from experimentally infected chicks to uninoculated chicks housed in the same isolator units. Five days after two seeder chicks in each group of 12 were inoculated with oral doses of approximately 10(3) S. enteritidis cells at 8 days of age, ceca and livers were sampled from seeder chicks and from their contact-exposed penmates. On the basis of the detection of S. enteritidis in cecal samples, phage type 4 strains were transmitted horizontally at a significantly lower frequency than were strains of other phage types. Nevertheless, two of three phage type 4 strains evaluated were very highly invasive.