Susceptibility of newborn and adult guinea pigs to Mycobacterium intracellulare and M. kansasii.

Six groups of guinea pigs, each consisting of 30 3-month-old and 20 7-day-old animals, received intraperitoneal inoculations with one of four strains of Mycobacterium intracellulare or one of two strains of M. kansasii. Three similar control groups received either an intraperitoneal injection of M. tuberculosis, no injection, or a sterile injection. Guinea pigs were sacrificed at 3, 5, 10, 20, 30, and 90 days. Lungs, spleen, liver and peritoneal fluid were cultured. Lungs were also examined histologically for inflammatory response. All the guinea pigs sacrificed within 20 days after inoculation showed positive cultures at nearly all sites. Thirty days after inoculation significantly more of the young guinea pigs had positive cultures, and the distribution of mycobacteria in their tissues was wider than was observed with the adult animals. At 90 days, the bacteriological results were similar for both groups. This histological findings were generally similar for both age groups, although acute reactions persisted longer in the young animals. All guinea pigs injected with M. tuberculosis died spontaneously within 90 days after inoculation and showed positive cultures at all sites. The results of the present study indicate that young guinea pigs are more susceptible to M. intracellulare and M. kansasii than are adult animals and should be preferred to old animals for diagnostic inoculations.