title: Efficacy of simulated cefditoren versus amoxicillin-clavulanate free concentrations in countering intrastrain ftsI gene diffusion in Haemophilus influenzae.
abstract: This study explores the effects of cefditoren (CDN) versus amoxicillin-clavulanic acid (AMC) on the evolution (within a single strain) of total and recombined populations derived from intrastrain ftsI gene diffusion in β-lactamase-positive (BL⁺) and β-lactamase-negative (BL⁻) Haemophilus influenzae. DNA from β-lactamase-negative, ampicillin-resistant (BLNAR) isolates (DNA(BLNAR)) and from β-lactamase-positive, amoxicillin-clavulanate-resistant (BLPACR) (DNA(BLPACR)) isolates was extracted and added to a 10⁷-CFU/ml suspension of one BL⁺ strain (CDN MIC, 0.007 μg/ml; AMC MIC, 1 μg/ml) or one BL⁻ strain (CDN MIC, 0.015 μg/ml; AMC MIC, 0.5 μg/ml) in Haemophilus Test Medium (HTM). The mixture was incubated for 3 h and was then inoculated into a two-compartment computerized device simulating free concentrations of CDN (400 mg twice a day [b.i.d.]) or AMC (875 and 125 mg three times a day [t.i.d.]) in serum over 24 h. Controls were antibiotic-free simulations. Colony counts were performed; the total population and the recombined population were differentiated; and postsimulation MICs were determined. At time zero, the recombined population was 0.00095% of the total population. In controls, the BL⁻ and BL⁺ total populations and the BL⁻ recombined population increased (from ≈3 log₁₀ to 4.5 to 5 log₁₀), while the BL⁺ recombined population was maintained in simulations with DNA(BLPACR) and was decreased by ≈2 log₁₀ with DNA(BLNAR). CDN was bactericidal (percentage of the dosing interval for which experimental antibiotic concentrations exceeded the MIC [ft>MIC], >88%), and no recombined populations were detected from 4 h on. AMC was bactericidal against BL⁻ strains (ft>MIC, 74.0%) in DNA(BLNAR) and DNA(BLPACR) simulations, with a small final recombined population (MIC, 4 μg/ml; ft>MIC, 30.7%) in DNA(BLPACR) simulations. When AMC was used against the BL⁺ strain (in DNA(BLNAR) or DNA(BLPACR) simulations), the bacterial load was reduced ≈2 log₁₀ (ft>MIC, 44.3%), but 6.3% and 32% of the total population corresponded to a recombined population (MIC, 16 μg/ml; ft>MIC, 0%) in DNA(BLNAR) and DNA(BLPACR) simulations, respectively. AMC, but not CDN, unmasked BL⁺ recombined populations obtained by transformation. ft>MIC values higher than those classically considered for bacteriological response are needed to counter intrastrain ftsI gene diffusion by covering recombined populations.
authors.affiliation: Microbiology Department, School of Medicine, Universidad Complutense, Avda. Complutense s/n, 28040 Madrid, Spain.
authors.forename: Natalia
authors.initials: N
authors.lastname: González
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Aguilar
authors.forename: David
authors.initials: D
authors.lastname: Sevillano
authors.forename: Maria-Jose
authors.initials: MJ
authors.lastname: Giménez
authors.forename: Luis
authors.initials: L
authors.lastname: Alou
authors.forename: Fabio
authors.initials: F
authors.lastname: Cafini
authors.forename: Martha
authors.initials: M
authors.lastname: Torrico
authors.forename: Ana-Maria
authors.initials: AM
authors.lastname: López
authors.forename: Pilar
authors.initials: P
authors.lastname: Coronel
authors.forename: Jose
authors.initials: J
authors.lastname: Prieto
mesh_terms: D019980:Amoxicillin-Potassium Clavulanate Combination / Q000493:pharmacokinetics / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002511:Cephalosporins / Q000493:pharmacokinetics / Q000494:pharmacology*; D004058:Diffusion; D024881:Drug Resistance, Bacterial; D005798:Genes, Bacterial; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D008826:Microbial Sensitivity Tests; D001618:beta-Lactamases / Q000032:analysis
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D019980:Amoxicillin-Potassium Clavulanate Combination; C073460:cefditoren; D001618:beta-Lactamases