The origin of endogenous Proteus mirabilis bacteriæmia in irradiated mice

Studies were conducted on mice which were normal carriers of Proteus mirabilis and died with Proteus bacteremia after irradiation. The distribution of P. mirabilis in male C57B1 mice was studied in an attempt to correlate the presence of Proteus in the respiratory or intestinal tract with the occurrence of Proteus bacteremia after irradiation. Nasal swabs, nasopharyngeal swabs, and fresh feces were repeatedly cultured during a period of several weeks preceding x irradiation with a LD100 of 700 r. The animals were classified as permanent carriers, temporary carriers, intermittent carriers, and noncarriers. The permanent carriers commonly died with Proteus bacteremia after irradiation; this type of bacteremia was rarely encountered in the noncarriers. The findings showed that Proteus bacteremia was positively correlated with the presence of Proteus in cultures of the nasopharynx. It concluded that the portal of entry for this type of bacteremia is located in the respiratory tract and not in the intestinal tract. Edema of the snout in irradiated mice was almost characteristic of Proteus infection and may be due to involvement of the nasal cavity. Proteus bacteremia has repeatedly been mentioned in support of the hypothesis of the enteric origin of irradiation bacteremia. The present findings, however, showmore » that it is wrong to assume that the organism must originate from the intestine.« less