Effect of repeated irradiation on various characteristics of Salmonella.

Four Salmonella serotypes which had been subjected to either 15 or 20 cycles of irradiation and subculture were examined for possible changes induced by the treatment. With three serotypes virulence remained unchanged, and with one serotype a reduction had occurred. A few minor changes in the biochemical characteristics occurred in some instances, but with all cultures the serological property was affected to some extent. Lag times and growth rates of the treated cultures were not altered, but the maximal viable population was usually less than that for untreated cultures.