Salmonella enteriditis serotype Amsterdam in a commercial rat colony

Salmonella enteriditis serotype Amsterdam was isolated from the feces of 10 of 25 barrier maintained Fischer 344 rats in a commercial colony of over 35,000 animals. During the subsequent 3-month period, a small percentage of asymptomatic rats remained culture-positive for Salmonella despite an extensive program of killing animals with positive fecal cultures. The failure of this procedure to eradicate Salmonella from the colony led to the eventual destruction of the entire colony. Salmonella enteriditis serotype Amsterdam was cultured from wild rodent feces on a cracked well head casing which covered the shaft to the well that provided water for the barrier facility; an identical Salmonella serotype was also isolated from an animal care technician working with animals in this barriered colony. The technician was asymptomatic, and the organism was cultured on only one occasion. This outbreak was retrospectively attributed to water-borne Salmonella which apparently survived treatment with a faulty chlorinator.