Affiliation:
1. Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom
Abstract
ABSTRACT
Auxotrophic mutants of
Mycobacterium tuberculosis
have been proposed as new vaccine candidates. We have analyzed the virulence and vaccine potential of
M. tuberculosis
strains containing defined mutations in genes involved in methionine (
metB
), proline (
proC
), or tryptophan (
trpD
) amino acid biosynthesis. The
metB
mutant was a prototrophic strain, whereas the
proC
and
trpD
mutants were auxotrophic for proline and tryptophan, respectively. Following infection of murine bone marrow-derived macrophages, H37Rv and the
metB
mutant strain survived intracellularly for over 10 days, whereas over 90% of
proC
and
trpD
mutants were killed during this time. In SCID mice, both H37Rv and the
metB
mutant were highly virulent, with mouse median survival times (MST) of 28.5 and 42 days, respectively. The
proC
mutant was significantly attenuated (MST, 130 days), whereas the
trpD
mutant was essentially avirulent in an immunocompromised host. Following infection of immunocompetent DBA mice with H37Rv, mice survived for a median of 83.5 days and the
metB
mutant now showed a clear reduction in virulence, with two of five infected mice surviving for 360 days. Both
proC
and
trpD
mutants were avirulent (MST of >360 days). In vaccination studies, prior infection with either the
proC
or
trpD
mutant gave protection equivalent (
proC
mutant) to or better (
trpD
mutant) than BCG against challenge with
M. tuberculosis
H37Rv. In summary,
proC
and
trpD
genes are essential for the virulence of
M. tuberculosis
, and mutants with disruptions in either of these genes show strong potential as vaccine candidates.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology