Members of the
beta-lactam class of
antibiotics, which inhibit the bacterial
d,d-
transpeptidases involved in cell wall biosynthesis, have never been used systematically in the treatment of
Mycobacterium tuberculosis infections because of this organism's resistance to
beta-lactams. The critical resistance factor is the constitutive production of a chromosomally encoded, Ambler class A
beta-lactamase, BlaC in M.
tuberculosis. We show that BlaC is an extended spectrum
beta-lactamase (ESBL) with high levels of
penicillinase and
cephalosporinase activity as well as measurable activity with
carbapenems, including
imipenem and
meropenem. We have characterized the
enzyme's inhibition by three FDA-approved
beta-lactamase inhibitors:
sulbactam,
tazobactam, and
clavulanate.
Sulbactam inhibits the
enzyme competitively and reversibly with respect to
nitrocefin.
Tazobactam inhibits the
enzyme in a time-dependent manner, but the activity of the
enzyme reappears due to the slow hydrolysis of the covalently acylated
enzyme. In contrast,
clavulanate reacts with the
enzyme quickly to form hydrolytically stable, inactive forms of the
enzyme that have been characterized by mass spectrometry.
Clavulanate has potential to be used in combination with approved
beta-lactam antibiotics to treat multi-
drug resistant (MDR) and extremely
drug resistant (XDR) strains of M.
tuberculosis.