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 penicillinbinding 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 3V) (one strain) or PBP2b (T 445 3A) (one strain). All eight PISP strains had at least two alterations--T 338 3P or A or H 394 3Y in PBP2X and T 445 3A in BPB2b. All PRSP strains had the same changes seen in PISP strains, as well as T 371 3A or S substitutions in PBP1a. The two most resistant PRSP strains had a second change in PBP2x (M 339 3F) 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.The worldwide incidence of infections caused by Streptococcus pneumoniae isolates resistant to penicillin and other antimicrobial agents has increased at an alarming rate during the past 2 decades (2). In a recent U.S. study, penicillin-nonsusceptible pneumococci were found in 50.4% of 1,476 strains, and the prevalence of macrolide-resistant strains was 65.6% in penicillin-resistant strains (20). The higher the penicillin MIC, the more likely it is that the strain will be multidrug resistant. Multidrug-resistant (including resistance to fluoroquinolones) pneumococci have been reported in Hong Kong (19), Canada (7), and Spain (24), and the clonal spread of these strains from country to country and continent to continent is of concern. There is an urgent need for oral ␤-lactams that can be used for outpatient treatment of infections, such as pneumonia, bronchitis, sinusitis, and otitis media, caused by penicillin-and macrolide-nonsusceptible pneumococci. Amoxicillin has excellent in vitro antipneumococcal activity (1, 3, 18) and has been shown to select for resistant laboratory mutants less frequently than other compounds (27,29). Previous studies have documented the potent in vitro antipneumococcal activity of cefditoren, with MICs at which 50 and 90% of isolates are inhibited of 0.5 and 1.0 g/ml, respectively, against penicillin-resistant strains (35,36). Cefditoren a...

Sulfonamide-1,2,4-thiadiazole Derivatives as Antifungal and Antibacterial Agents: Synthesis, Biological Evaluation, Lipophilicity, and Conformational Studies

“…Here we demonstrate the conformational properties of the most active compounds 5m, 5h and of the lowest activity compound 5a. The solvent used in NMR analysis is DMSO-d 6 and not D 2 O because of little solubility of tested compounds in aqueous media. Selection of the solvent though is not inadequate since drug's bioactive conformation is finally determined from the environment of the active site of the target protein.…”

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Antibiotic Resistance in Bacteria and Its Future for Novel Antibiotic Development

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Clonal spread of β-lactamase-producing amoxicillin–clavulanate-resistant (BLPACR) strains of non-typeable Haemophilus influenzae among young children attending a day care in Japan

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