The origin of induced Pseudomonas aeruginosa Bacteriæmia in irradiated mice

Experiments were conducted in 2 strains of mice lethally irradiated with whole-body doses of 200-kv x rays and subsequently inoculated with an organism considered to be a normal inhabitant of the mouse. The LD/sub 100/ doses for the C57B1 and CBA mice used were found to be 700 and 675 r, respectively; all animals were exposed to 700 r. A bacterial culture (P. aeruginosa) was introduced into the respiratory or intestinal tract of mice after irradiation. Nasal inoculation on the 3rd, 4th, or 5th day after irradiation always led to bacteremia, and the mean survival time after inoculation varied between 2 and 21/2 days. Gastric instillation of the organisms gave bacteremia in about 60% of animals. The frequency of Pseudomonas bacteremia following nasal inoculation on the 2nd day after irradiation was correlated with the presence of the organism in the respiratory tract and was independent of its presence in the intestine. Cervical lymph glands, liver, and spleen were infected in the prebacteremic stage. After gastric instillation, accidental infection of the larynx occurred in 60% of the animals. It is concluded that Pseudomonas bacteremia originates from the respiratory tract whether the organism is inoculated via the respiratory tract or via themore » stomach. Local damage to the respiratory mucosa, invasiveness of the inoculated strain, and impairment of cellular defense appeared to be the principal factors leading to bacteremia. The fact that the cervical lymph glands were involved, and not the mesenteric glands, indicates that the portal of entry is located in the respiratory mucosa and not in the intestinal tract. The occurrence of Pseudomonas bacteremia in about 60% of mice inoculated by gastric installation can be explained by the frequent infection of the larynx resulting from this procedure. (BBB)« less