Comparison of the efficacies of oral beta-lactams in selection of Haemophilus influenzae transformants with mutated ftsI genes

[Three keys to the appropriate choice of oral antibiotic treatment in the respiratory tract infections]

Exacerbation of chronic obstructive pulmonary disease and community-acquired pneumonia are the most frequent infections of the lower respiratory tract in daily clinical practice. Antibiotic selection is a crucial component in its treatment and, in most cases, it is performed empirically. Scientific societies make therapeutic recommendations based on scientific evidence and / or expert recommendations that are of great help to clinicians. Beta-lactams, fluoroquinolones and macrolides are the most commonly used drugs for oral administration. From a practical point of view, there are three keys to the appropriate choice of oral antibiotic treatment, which are the effectiveness, safety and the ecological impact on the patient's microbiota, including the development of resistance, which will be assessed in depth in this review.

Design, synthesis, and evaluation of prodrugs of ertapenem

Carbapenems are intravenous lifesaving hospital antibiotics. Once patients leave the hospital, they are sent home with antibiotics other than carbapenems since they cannot be administered orally due to lack of oral absorption primarily because of very highly polarity. A prodrug approach is a bona fide strategy to improve oral absorption of compounds. Design and synthesis, in vitro and in vivo evaluation of diversified prodrugs of ertapenem, one of the only once daily dosed carbapenems is described. Many of the prodrugs prepared for evaluation are rapidly hydrolyzed in rat plasma. Only bis-(5-methyl-2-oxo-1,3-dioxol-4-yl)methyl (medoxomil) ester prodrug was rapidly hydrolyzed in most of the plasmas including rat, human, dog, and monkey. Although the rate of conversion of ertapenem diethyl ester prodrug (6) was slow in in vitro plasma hydrolysis, it showed the best in vivo pharmacokinetic profile in dog by an intraduodenal dosing giving >31% total oral absorption.

Efficacy of simulated cefditoren versus amoxicillin-clavulanate free concentrations in countering intrastrain ftsI gene diffusion in Haemophilus influenzae

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.

Drug resistance in community-acquired respiratory tract infections: role for an emerging antibacterial

The nasopharynx is the ecological niche where evolution towards resistance occurs in respiratory tract isolates. Dynamics of different bacterial populations in antibiotic-free multibacterial niches are the baseline that antibiotic treatments can alter by shifting the competitive balance in favor of resistant populations. For this reason, antibiotic resistance is increasingly being considered to be an ecological problem. Traditionally, resistance has implied the need for development of new antibiotics for which basic efficacy and safety data are required prior to licensing. Antibiotic development is mainly focused on demonstrating clinical efficacy and setting susceptibility breakpoints for efficacy prediction. However, additional information on pharmacodynamic data predicting absence of selection of resistance and of resistant subpopulations, and specific surveillance on resistance to core antibiotics (to detect emerging resistances and its link with antibiotic consumption in the community) are valuable data in defining the role of a new antibiotic, not only from the perspective of its therapeutic potential but also from the ecologic perspective (countering resistances to core antibiotics in the community). The documented information on cefditoren gleaned from published studies in recent years is an example of the role for an emerging oral antibacterial facing current antibiotic resistance in community-acquired respiratory tract infections.

Diverse mutations in the ftsI gene in ampicillin-resistant Haemophilus influenzae isolates from pediatric patients with acute otitis media

To clarify molecular changes in beta-lactamase-nonproducing, ampicillin-resistant (BLNAR) Haemophilus influenzae, which is increasing in pediatric patients with acute otitis media (AOM) in Japan, we identified amino acid (aa) substitutions in penicillin-binding protein 3 for the BLNAR strains. Of 191 H. influenzae strains isolated from middle ear fluid of pediatric AOM patients between October 2005 and March 2008, BLNAR strains determined by PCR accounted for 49.2%. Of the BLNAR strains, 91.5% possessed 4 aa substitutions: Met377Ile, Ser385Thr, Leu389Phe, and either Asn526Lys or Arg517His. Additionally, the emergence of BLNAR strains possessing a new aa substitution of Val329Ala in the conserved aa motif of Ser327-Thr-Val-Lys, or Val511Ala adjacent to the conserved aa motif of Lys512-Thr-Gly, was noted. Transformation of the ftsI gene into the Rd reference strain (ATCC 51907) demonstrated that these two aa substitutions reduced susceptibility to amoxicillin more than to cephalosporins. Pulsed-field gel electrophoretic profiles of BLNAR strains were highly diverse. These results suggested that inadequate antibiotic use may increase BLNAR strains by selecting mutations in the ftsI gene and that such use may have favored the new aa substitutions.