Mouse Foot-Pad Infections with Acid-Fast Bacilli: with Special Reference to the Effect of Environmental Temperature on Mice

Different temperatures were investigated comparatively for effect on infections of the mouse foot-pad with various acid-fast bacilli. The strains used were the Iwata, a strain of freshly isolated virulent tubercle bacilli, and the ML (M. kansasii), P5 (Group II), P25 (Group III), ATCC6841 (M. fortuitum), and ATCC927 (M. marinum), strains of atypical acid-fast bacilli. Nine or ten mice were infected with one strain after being adapted to temperatures of 10°, 20°, or 33°C in 14 days. They were inoculated subcutaneously with 105-106 viable organisms into the left hind foot-pad and examined daily for the appearance of foot-pad swelling. For each strain two to four mice were kept at one of the three different temperatures and sacrificed on the 14th, 28th, or 42nd day after inoculation. At autopsy gross finding on the foot-pad, lung, liver, kidney, and spleen were recorded, and each organ was cultured for viable unit count. The optimal temperature for the occurrence of foot-pad swelling was different with the strain, as well as by the period of observation. In general, it was higher in mice kept at 10° and/or 20°C than in those kept at 33°C, except those infected with M. kansasii. In mice infected with M. kansasii, the greatest swelling was produced at an air temperature of 33°C throughout the experiment. Acid-fast bacilli recovered from the foot-pad were larger in number in mice maintained at 10° and 20°C than in those kept at 33°C. Gross lesions in the visceral organs were rarely encountered in mice infected with strain Iwata, P5, or ATCC6841. Viable units recovered from the visceral organs were very few, if any. Histologically, the lesions produced in the foot-pads were granulomas.