Colonization with nontuberculous mycobacteria is associated with positive tuberculin skin test reactions in the common marmoset (Callithrix jacchus).

Mycobacterium tuberculosis infections can result in significant morbidity and mortality in nonhuman primate colonies. Preventative health programs designed to detect infection routinely include tuberculin skin testing (TST). Because Mammalian Old Tuberculin used for TST contains antigens common to a variety of mycobacterial species, false-positive results can occur in animals sensitized to nontuberculous mycobacteria (NTM). Over 11 mo, a large colony of common marmosets (Callithrix jacchus) demonstrated a 3.6% prevalence of equivocal or positive TST reactions (termed 'suspect reactions'). Culture of gastric aspirates, bronchoalveolar lavage fluid, and feces revealed a single animal with a positive fecal culture for Mycobacterium gordonae. PCR amplification of M. gordonae DNA in feces collected from animals with suspect TST reactions (demonstrating a 66.7% colonization rate) and colony controls (demonstrating a 14.3% colonization rate) revealed a significant association between suspect TST reactions and intestinal colonization. Gross and histopathologic evaluation revealed a multifocal lymphadenopathy and granulomatous lymphadenitis in 2 of 4 TST-positive marmosets examined. Counter to expectations, granulomatous lymphoid tissue was culture-positive for M. kansasii rather than M. gordonae. Detection of M. gordonae in the feces of TST-suspect animals likely represents an apathogenic intestinal colonization that may serve as an indicator of NTM exposure, whereas evidence of histopathologic disease is associated with the more pathogenic M. kansasii. Although a high index of suspicion for M. tuberculosis should always be maintained, colonization with NTM organisms represents a cause of suspect TST reactions in common marmosets.