Experimental animal infections with Mycoplasma hominis and Ureaplasma urealyticum

Subcutaneous tissue cavities in mice and guinea pigs were infected with human isolates of Ureaplasma urealyticum and Mycoplasma hominis. The minimal infective dose for M. hominis was as low as less than 10 color-changing units (CCU) for mice and 10(2) CCU for guinea pigs. The minimal infective dose for U. urealyticum was as low as less than 10 CCU for mice and 10(4) CCU for guinea pigs. Mouse infections with either U. urealyticum or M. hominis persisted for 1 day to greater than 4 months. Guinea pigs remained infected for up to 4 weeks. Two M. hominis isolates were similar in their ability to infect subcutaneous tissue cavities but two U. urealyticum isolates varied in their ability to infect the cavities. The histopathology of the M. hominis and U. urealyticum infections was similar: an initial intense polymorphonuclear response with giant cells, followed in 4 weeks by histiocytes and giant cells with some plasma cells and lymphocytes.