Rapid differentiation of "Mycobacterium canettii" from other mycobacteriumtuberculosis complex organisms by PCR-Restriction analysis of the hsp65 gene

A total of 102 isolates of the Mycobacterium tuberculosis complex, includin g available "M. canettii" isolates, were studied by PCR-restriction analysi s of a 441-bp fragment of the hsp65 gene. PRA upon HhaI enzyme digestion (G CGC) allowed easy differentiatiation of "M. canettii" from other members of the M. tuberculosis complex (three bands of 260, 105, and 60 bp for "M. ca netti," compared to four bands of 185, 105, 75, and 60 bp for other members of the M. tuberculosis complex). Sequencing of the 441-bp hsp65 fragment o f "M. canettii" isolates showed the disappearance of an HhaI site at positi on 235 due to a C-to-T transition that corresponded to position 631 of the homologous hsp65 gene of M. tuberculosis H37Rv. Considering that "M. canett ii" may also exist as a stable rough morphotype, we suggest that the true n umber of "M. canettii" isolates may be underestimated in clinical microbiol ogy laboratories.