Multidrug- and extensively drug-resistant strains of
Mycobacterium tuberculosis are resistant to first- and second-line drug
regimens and resulted in 210,000 fatalities in 2013. In the current
study, we screened a library of aquatic bacterial natural product
fractions for their ability to inhibit this pathogen. A fraction from a
Lake Michigan bacterium exhibited significant inhibitory activity, from
which we characterized novel diazaquinomycins H and J. This
antibiotic class displayed an in vitro activity profile similar or superior
to clinically used anti-tuberculosis agents and maintained this potency
against a panel of drug-resistant M. tuberculosis strains. Importantly,
these are among the only freshwater-derived actinomycete bacterial
metabolites described to date. Further in vitro profiling against a broad panel of bacteria indicated that this antibiotic class
selectively targets M. tuberculosis. Additionally, in the case of this pathogen we present evidence counter to previous reports that
claim the diazaquinomycins target thymidylate synthase in Gram-positive bacteria. Thus, we establish freshwater environments as
potential sources for novel antibiotic leads and present the diazaquinomycins as potent and selective inhibitors of M. tuberculosis.