title: A conservative amino acid mutation in the chromosome-encoded dihydrofolate reductase confers trimethoprim resistance in Streptococcus pneumoniae.
abstract: Multidrug-resistant Streptococcus pneumoniae strains have emerged over the past decade at an alarming rate. The molecular mechanism of trimethoprim resistance was investigated in 5 pneumococcal strains isolated in the Washington, DC, area from patients with invasive infections. Cloning and sequencing of the trimethoprim resistance determinant from these pneumococci indicated that an altered chromosome-encoded dihydrofolate reductase (DHFR) was responsible for the observed resistance. Comparison of DHFR sequences from pneumococcal strains with various susceptibilities to trimethoprim, together with site-directed mutagenesis, revealed that substitution of isoleucine-100 with a leucine residue resulted in trimethoprim resistance. Hydrogen bonding between the carbonyl oxygen of isoleucine-100 and the 4-amino group of trimethoprim is proposed to play a critical role in the inhibition of DHFR by trimethoprim. This enzyme-substrate model should facilitate the design of new antibacterial agents with improved activity against S. pneumoniae.
authors.affiliation: Vaccine and Therapeutic Development Section, Oral Infection and Immunity Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892-4350, USA. apikis@yoda.nidr.nih.gov
authors.forename: A
authors.initials: A
authors.lastname: Pikis
authors.forename: J A
authors.initials: JA
authors.lastname: Donkersloot
authors.forename: W J
authors.initials: WJ
authors.lastname: Rodriguez
authors.forename: J M
authors.initials: JM
authors.lastname: Keith
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001483:Base Sequence; D002876:Chromosomes, Bacterial; D017124:Conserved Sequence; D004269:DNA, Bacterial; D004352:Drug Resistance, Microbial / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D014295:Trimethoprim / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D014295:Trimethoprim; D013762:Tetrahydrofolate Dehydrogenase