Open AccessIn Vitro Efficacy of New Antifolates against Trimethoprim-Resistant Bacillus anthracis
Author(s) -
Esther W. Barrow,
Jürg Dreier,
Stefan Reinelt,
Philip C. Bourne,
William W. Barrow
Publication year - 2007
Publication title -
antimicrobial agents and chemotherapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.07
H-Index - 259
eISSN - 1070-6283
pISSN - 0066-4804
DOI - 10.1128/aac.00628-07
Subject(s) - bacillus anthracis , broth microdilution , in vitro , microbiology and biotechnology , antifolate , trimethoprim , minimum inhibitory concentration , bacillaceae , biology , bacillales , chemistry , biochemistry , bacteria , antibiotics , immunology , methotrexate , antimetabolite , genetics , bacillus subtilis
Bacillus anthracis is innately resistant to trimethoprim (TMP), a synthetic antifolate that selectively inhibits several bacterial dihydrofolate reductases (DHFRs) but not human DHFR. Previously, we were able to confirm that TMP resistance inB. anthracis (MIC > 2,048 μg/ml) is due to the lack of selectivity of TMP for theB. anthracis DHFR (E. W. Barrow, P. C. Bourne, and W. W. Barrow, Antimicrob. Agents Chemother. 48:4643-4649, 2004). In this investigation, 24 2,4-diaminopyrimidine derivatives, representing a class of compounds with dihydrophthalazine side chains, were screened for their in vitro effects onB. anthracis Sterne and their selectivities for theB. anthracis DHFR. MICs were obtained by a colorimetric (Alamar blue) broth microdilution assay. Purified human recombinant DHFR (rDHFR) andB. anthracis rDHFR were used in a validated enzyme assay to determine the 50% inhibitory concentrations (IC50 s) and the selectivity ratios of the derivatives. The MICs ranged from 12.8 to 128 μg/ml for all but nine compounds, for which the MICs were ≥128 μg/ml. The IC50 values forB. anthracis rDHFR ranged from 46 to 600 nM, whereas the IC50 values for human rDHFR were >16,000 nM. This is the first report on the in vitro inhibitory actions of this class of antifolates against TMP-resistantB. anthracis isolates. The selective inhibition ofB. anthracis rDHFR and the in vitro activity againstB. anthracis demonstrate that members of this class of compounds have the potential to be developed into clinically important therapeutic choices for the treatment of infections caused by TMP-resistant bacteria, such asB. anthracis .