Protective abilities of live avirulent strains of M. tb complex vary widely.

2003 JAN 1 - (NewsRx.com & NewsRx.net) -- According to researchers in New Zealand, "A better tuberculosis vaccine is urgently required to control the continuing epidemic. Molecular techniques are now available to produce a better live vaccine than BCG [bacillus Calmette-Guerin] by producing avirulent strains of the Mycobacterium tuberculosis complex with known gene deletions."

D.M. Collins and colleagues produced 1000 illegitimate recombinants of M. bovis "by illegitimate recombination with fragments of mycobacterial DNA containing a kanamycin resistance gene."

Of these, "[e]ight recombinant strains were selected on the basis of their inability to grow when stationary-phase cultures were inoculated into minimal medium. Five of these recombinants were found to be avirulent when inoculated into guinea pigs," the researchers said.

"Two of the avirulent recombinants produced vaccine efficacy comparable to BCG against an aerosol challenge in guinea pigs with M. bovis. One of these recombinants had an inactivated glnA2 gene encoding a putative glutamine synthetase. Transcriptional analysis showed that inactivation of glnA2 did not affect expression of the downstream glnE gene," said Collins and associates.

"The other recombinant had a block of 12 genes deleted, including the sigma factor gene sigG," they wrote.

"Two avirulent ...