Relationship of body temperature to localization of mycetomas caused by Nocardia brasilensis in a murine model

Objective. Nocardia brasiliensis causes mycetomas localized in the cutaneou s and subcutaneous tissues as well as the muscle or bone of the feet, hands , arms, and body trunk. However, it may also cause systemic nocardiosis inv olving the lungs, brain or other internal organ systems. Mycetomas and syst emic nocardiosis caused by N. brasiliensis rarely occur in the same individ ual. The mechanisms for these differences are not known. Most strains of N. brasiliensis are sensitive to temperatures greater than 35 degreesC, and t hey do not grow above 40 degreesC. Material and methods. Two strains, which differed in their optimal growth t emperature, were selected. Strain UC-50, isolated from a patient with disse minated disease, had optimal growth in broth at 37 to 39 degreesC. In contr ast, strain UC-88, isolated from a mycetoma of the foot, grew optimally at 34 degreesC, and it did not grow at 39 degreesC. Suspensions of approximate ly 2 x 10(6) Colony Forming Unit (CFU) of either UC-50 or UC-88 at mid-log phase of growth were injected i.v. into Swiss Webster mice. At 3 hrs, 7 and 14 days, and 1, 2, 3, 4, and 5 months after infection, mice were sacrifice d, 15 regions of the body were removed, and the CFU per gram of tissue dete rmined. The body temperature of these mice was monitored rectally. Resuslts and conclusions. Animals not overtly ill, had a temperature that v aried from 38 to 39 degreesC, whereas mice that appeared sick had a reduced temperature (p < 0.01). Strain UC-50 induced progressive abscesses in the lungs, brain, kidneys, adrenals, and spleen of 100 % of the mice. In contra st, strain UC-88 rarely induced abscesses in the internal organs, but inste ad, induced mycetomas in the feet, tail, and nasal region of 100 % of the a nimals. The lesions increased in size over a 5 month time in all mice infec ted with UC-50 or UC-88. These data indicate that the differential suscepti bilities of N. brasiliensis to temperature contribute to differences in loc alization of lesions, and suggest heterogeneity within the N. brasiliensis taxon.