[Cutaneous infection by Mycobacterium fortuitum biovariant "third group"--a case report and bacteriological examination of the isolate].

A 22-year-old woman with ten-year history of atopic dermatitis first noticed an erythematous ++, indurated, and fluctuant lesion on her back six month prior to visiting our hospital in February 1989. The dusky red skin lesion gradually spread to the right side of her trunk and drained small amount of purulent or serosanguineous fluid. A skin biopsy specimen showed mixed pattern of nonspecific inflammatory infiltrate and granulomatous infiltrate in the dermis. A culture of the biopsy specimen showed a rapidly growing atypical acid-fast bacteria, which was identified as Mycobacterium fortuitum and classified as biovariant "third group" by positive growth on mannitol and inositol. Minimum inhibitory concentrations (MICs) of different antimicrobial agent using broth medium showed that the isolate was susceptible to the new quinolones such as ofloxacin and ciprofloxacin. The patient responded to treatment with doxycycline followed by with ofloxacin. Subspecies classification and antibiotic susceptibilities were discussed with special reference to treatment of rapidly growing mycobacteria.