Atypical mycobacteria and the xenograft valve.

During a 4 month interval, cultures taken at the time of porcine xenograft valve implantation grew a fastidious atypical mycobacterium, Mycobacterium chelonei (Runyon's groups IV), in eight of 20 patients. Initial growth occurred at 2 to 3 weeks in thioglycollate broth only; detailed biochemical and bacteriologic evaluation demonstrates altered catalase activity accounting for its initial slow growth. Only one patient has manifested clinical evidence of infection 5 months after mitral valve replacement. A large pericardial effusion required pericardiectomy. Pericardial tissue and fluid have grown M. chelonei with the same growth characteristics as the initial valve culture. It is recommended that manufacturers of xenograft valve bioprostheses maintain a quarantine of 6 weeks until cultures, smears of culture broth, and microscopic evaluation of aortic wall coupons are negative. Users of these prostheses should keep cultures for a minimum of 3 weeks. Should positive cultures result, antimicrobial therapy should be considered only with clinical evidence of infection.