Affiliation:
1. Department of Pathology, University of California, San Diego, La Jolla, California 92093-0640
Abstract
ABSTRACT
Mycobacterium tuberculosis
grows within the phagocytic vacuoles of macrophages, where it encounters a moderately acidic and possibly nutrient-restricted environment. Other mycobacterial species encounter acidic conditions in soil and aquatic environments. We have evaluated the influence of pH and divalent cation levels on the growth of
M. tuberculosis
and seven other mycobacterial species. In a defined medium, the growth of
M. tuberculosis
was very restricted by acidic pH. Higher levels of Mg
2+
were required for growth of
M. tuberculosis
in mildly acidic media (pH 6.0 to 6.5) compared to pH 7.0 medium. The divalent cations Ca
2+
, Zn
2+
, or Mn
2+
could not replace Mg
2+
during growth at pH 6.25, but Ca
2+
could at least partially substitute for Mg
2+
during growth at pH 7.0. Among eight species of mycobacteria tested, there was a diversity of growth rates in media with acidic pH and low Mg
2+
levels.
M. tuberculosis
was the most restricted in growth at pH 6.0, and all of this growth required elevated levels of Mg
2+
.
M. kansasii
and
M. smegmatis
also grew very poorly in acidic media with limiting Mg
2+
.
M. fortuitum
,
M. marinum
,
M. scrofulaceum
,
M. avium
, and
M. chelonae
grew at pH 6.0 in an unrestricted manner. These results demonstrate that
M. tuberculosis
is unique among the mycobacteria in its extreme sensitivity to acid and indicate that
M. tuberculosis
must acquire sufficient Mg
2+
in order to grow in a mildly acidic environment such as within the phagosome of macrophages.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
94 articles.
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