Salmonella strain. Salmonella enterica serovar Typhimurium 4232 was used
both for isolation of wild-type phages and in challenge experiments. This strain
was originally isolated from diseased pigs and contains a nalidixic acid resistance
selection marker (7, 11). The phage treatment consisted of 14 wild-type phages
isolated specifically for this study, along with the Felix O1 phage (Universite´
Laval, Quebec, Canada).