Antimicrobial Activity of Tobramycin Against Respiratory Cystic Fibrosis Pseudomonas aeruginosa Isolates from Bulgaria

作者：Strateva T^*; Petrova G; Mitov I

来源：Journal of Chemotherapy, 2010, 22(6): 378-383.

DOI：10.1179/joc.2010.22.6.378

• Tobramycin
• antimicrobial activity
• Etest
• P. aeruginosa
• cystic fibrosis

Tobramycin solution for inhalation (TSI) (Novartis Pharmaceuticals) is indicated as chronic suppressive treatment for cystic fibrosis (CF) patients aged 6 years and older who are chronically infected by Pseudomonas aeruginosa. Inhaled administration of tobramycin assures high concentrations in the lungs of CF patients, improving the therapeutic ratio over that of parenteral tobramycin levels. Clinical and Laboratory Standards Institute (CLSI) breakpoints only consider parenteral levels and do not take into account these high antimicrobial concentrations. Therefore, the Spanish MENSURA Group has defined specific values for inhaled tobramycin when testing CF P. aeruginosa isolates (susceptible: minimal inhibitory concentration (MIC) <= 64 mu g/ml; resistant: >= 128 mu g/ml). In this study the antimicrobial activity of tobramycin against 120 respiratory CF P. aeruginosa isolates was determined by high-range Etest strips (LIOFILCHEM). Applying MENSURA breakpoints, 95% of the strains were categorized as susceptible. With CLSI breakpoints, the susceptibility rate decreased to 92.5%. The activity against non-mucoid P. aeruginosa was higher than that against mucoid isolates (MIC50=0.75 and MIC90=2 mu g/ml vs. MIC50=1 and MIC90=4 mu g/ml). The isolates obtained from patients untreated with TSI were more susceptible to the drug than those from patients receiving maintenance therapy with TSI (MIC50=0.75 and MIC90=1.5 mu g/ml vs. MIC50=1.5 and MIC90=6 mu g/ml). The isolates from patients with long-term P. aeruginosa colonization (over 5 years) revealed the highest tobramycin MICs (MIC50=1.00 and MIC90>1024 mu g/ml). In conclusion, tobramycin has excellent in vitro activity against the studied CF isolates. Some factors such as isolate morphotype, pre-administration of TSI and duration of colonization influence its activity. Whenever TSI is considered for therapy, the CF P. aeruginosa strains categorized as intermediate or resistant to tobramycin according to the CLSI criteria should be recategorized by using the MENSURA interpretive criteria.

• 出版日期2010-12