Setting: University-affiliated Mycobacteriology Reference Laboratory.
Objective: To determine the genetic differences of 25 BCG isolates rep
resenting 16 referenced substrains. Design: Non-randomized, observatio
nal study based on the visual comparison of the large restriction frag
ment (LRF) patterns created by digesting each BCG isolate's DNA with a
n infrequent cutting restriction endonuclease (DraI, AsnI, XbaI or Spe
I) and separating the resultant DNA fragments with pulsed field gel el
ectrophoresis. Results: The 25 BCG isolates gave 13 different DraI LRF
patterns, 11 different XbaI LRF patterns, 11 different AsnI LRF patte
rns, and 15 different SpeI LRF patterns. Examples of the same BCG subs
trains from different sources produced the same LRF patterns for only
2 of 6 substrains studied. These findings suggest a significant degree
of genetic diversity in this group of isolates despite a common origi
n. Four clinical BCG isolates gave LRF patterns identical to BCG Tice,
BCG Connaught or BCG Glare. The BCG LRF patterns more closely resembl
ed patterns of Mycobacterium bovis than M. tuberculosis. Conclusions:
LRF patterns can accurately identify specific BCG substrains and will
be useful in epidemiologic studies, monitoring vaccine production and
studies of BCG vaccine efficacy.