Efficacy of the Combination of Tobramycin and a Macrolide in an I n V itro Pseudomonas aeruginosa Mature Biofilm Model

Abstract

Respiratory disease is the main cause of morbidity and mortality in patients with cystic fibrosis (CF). In particular, patients suffer from chronic infection due to biofilm formation by opportunistic Pseudomonas aeruginosa (32). Therefore, there is an urgent need to develop alternative ways to treat biofilm-associated clinical infections. The aim of this study was to compare the antimicrobial effects in vitro of the combinations tobramycin-clarithromycin and tobramycin-azithromycin against five P. aeruginosa biofilms and to establish the most effective combination. We performed a kinetic study over a period of 28 days of a twice-daily coadministration of the combinations tobramycin-clarithromycin and tobramycin-azithromycin on 12-day-old, mature P. aeruginosa biofilms formed on microplate pegs for 4 clinical isolates and one laboratory strain (PAO1) to simulate the treatment of CF patients with tobramycin inhalation solution (TOBI) through aerosolization. A synergy between tobramycin and clarithromycin was recorded for 3/5 biofilms, with a bacterial decrease of more than 5 log. Conversely, we found an antagonistic activity when 4 g/ml tobramycin was administered with azithromycin at 2 g/ml for P. aeruginosa PAO1 and with azithromycin at 2, 20, 50, 100, and 200 g/ml for P. aeruginosa PYO1. Treatment with tobramycin at 4 g/ml combined with clarithromycin at 200 g/ml eradicated all five biofilms, while tobramycin-azithromycin at the same concentrations eradicated only three biofilms. Results of this study suggest that local administration of tobramycin and clarithromycin into the respiratory tract represents a better strategy than the combination tobramycin-azithromycin for the treatment of P. aeruginosa-associated pulmonary infections.

EnhancedIn VitroFormation and Antibiotic Resistance of Nonattached Pseudomonas aeruginosa Aggregates through Incorporation of Neutrophil Products

“…These early biofilms are extremely sensitive to dispersion by DNase, which restored antibiotic sensitivity. Interestingly, these simple aggregates, but not planktonic cultures, demonstrate azithromycin-induced antagonism toward tobramycin, as previously reported in other P. aeruginosa biofilm systems and in vivo (43)(44)(45)(46). Together, these findings support the usefulness of combining neutrophil products with P. aeruginosa to represent the biofilm phenotype within the CF airway more accurately.…”

“…Azithromycin has recently been found to antagonize the antipseudomonal activity of tobramycin in abiotic biofilm and mouse infection models (43)(44)(45)(46). Therefore, we tested P. aeruginosa planktonic cultures and neutrophil-enhanced aggregates for this drug interaction.…”

Inhaled antibiotics in the treatment of non-cystic fibrosis bronchiectasis: clinical and drug delivery perspectives

“…Drug Deliv. (2015) () alone [80]. Synergy was also reported in an in vitro study of ciprofloxacin and clarithromycin [81].…”

Antibiofilm Peptides: Potential as Broad-Spectrum Agents

“…For example, the aminoglycoside tobramycin and the macrolide clarithromycin show synergistic effects on clearing biofilms, although the individual antibiotics have only moderate effects (22). Conversely, combinations of tobramycin with other macrolides (such as azithromycin) show antagonistic effects, i.e., reduced effectiveness compared to that for individual usage (22). Thus, we need to gather more information about the mechanisms underlying synergistic treatment of biofilm infections.…”

“…Although some potential combinations to overcome adaptive resistance of biofilms have been demonstrated (e.g., using a colistin-tobramycin combination for clearing Pseudomonas-related pulmonary biofilm infection) (21,22), the molecular mechanisms driving the synergistic effects of two different antibiotic classes are poorly understood. For example, the aminoglycoside tobramycin and the macrolide clarithromycin show synergistic effects on clearing biofilms, although the individual antibiotics have only moderate effects (22). Conversely, combinations of tobramycin with other macrolides (such as azithromycin) show antagonistic effects, i.e., reduced effectiveness compared to that for individual usage (22).…”