Genetic analysis of Mycobacterium avium complex strains used for producing purified protein derivatives

For over a century, purified protein derivatives (PPD) have been used to detect mycobacterial infections in humans and livestock. Among these, reagents to detect infections by Mycobacterium avium complex organisms have been produced, but the utility of these reagents has not been clearly established due in part to limited biologic and immunologic standardization. Because there is little information about the strains used to produce these reagents (avian PPD, intracellulare PPD, scrofulaceum PPD, and Johnin), we have performed genetic characterizations of strains used to produce these products. Sequence analysis of 16S rRNA and the hsp65 gene provided results concordant with species designations provided for M. avium, Mycobacterium intracellulare, and Mycobacterium scrofulaceum organisms. For M. avium strains, comparative genomic hybridization was performed on a whole-genome DNA microarray, revealing one novel 7.9-kilobase genomic deletion in certain Johnin-producing strains, in addition to genomic variability inherent to the particular M. avium subspecies. Our findings indicate that considerable genomic differences exist between organisms used for reagents and the infecting organism being studied. These results serve as a baseline for potency studies of different preparations and should aid in comparative studies of newly discovered antigens for the diagnosis of infection and disease by M. avium complex organisms.