title: Effects of amino acid alterations in penicillin-binding proteins (PBPs) 1a, 2b, and 2x on PBP affinities of penicillin, ampicillin, amoxicillin, cefditoren, cefuroxime, cefprozil, and cefaclor in 18 clinical isolates of penicillin-susceptible, -intermediate, and -resistant pneumococci.
abstract: Amino acid alterations in or flanking conserved motifs making up the active binding sites of penicillin-binding proteins (PBPs) 1a, 2b, and 2x of pneumococci were correlated with changes in affinities of penicillin, ampicillin, amoxicillin, cefditoren, cefuroxime, cefprozil, and cefaclor for these PBPs. Four penicillin-susceptible (PSSP), eight penicillin-intermediate (PISP), and six penicillin-resistant (PRSP) pneumococci were studied by DNA sequencing of the penicillin-binding sites of the pbp1a, -2x, and -2b genes of strains and by determining 50% inhibitory concentrations of the seven agents for PBP1a, -2x, and -2b. Two PSSP strains had alterations in PBP2x (L(546)-->V) (one strain) or PBP2b (T(445)-->A) (one strain). All eight PISP strains had at least two alterations--T(338)-->P or A or H(394)-->Y in PBP2X and T(445)-->A in BPB2b. All PRSP strains had the same changes seen in PISP strains, as well as T(371)-->A or S substitutions in PBP1a. The two most resistant PRSP strains had a second change in PBP2x (M(339)-->F) in a conserved motif. The affinities of penicillin and ampicillin for all three PBPs were decreased for PRSP and most PISP strains. The affinity of amoxicillin for PBP1a and -2x was decreased only for PRSP. Cefaclor and cefprozil showed decreased affinity of PRSP but not PISP for all three PBPs. Cefuroxime showed decreased affinity of PISP and PRSP for PBP1a and -2x but no change for PBP2b. Cefditoren showed no difference in PBP affinity based on penicillin or cefditoren MICs, indicating a different PBP target for this agent. Overall, the MICs for and PBP affinities of the strains correlated with the changes found in the PBP active binding sites.
authors.affiliation: Department of Pathology, Hershey Medical Center, Hershey, Pennsylvania, USA.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Nagai
authors.forename: Todd A
authors.initials: TA
authors.lastname: Davies
authors.forename: Michael R
authors.initials: MR
authors.lastname: Jacobs
authors.forename: Peter C
authors.initials: PC
authors.lastname: Appelbaum
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D019881:Aminoacyltransferases; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D001426:Bacterial Proteins; D001665:Binding Sites / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002648:Child; D002675:Child, Preschool; D006602:Hexosyltransferases; D006801:Humans; D007223:Infant; D007769:Lactams / Q000378:metabolism* / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D008969:Molecular Sequence Data; D002267:Muramoylpentapeptide Carboxypeptidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010403:Penicillin Resistance; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000494:pharmacology; D010458:Peptidyl Transferases; D011008:Pneumococcal Infections / Q000382:microbiology; D017422:Sequence Analysis, DNA; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D007769:Lactams; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D019881:Aminoacyltransferases; C478701:penicillin-binding protein 2b, Streptococcus; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase