Tobramycin resistance in Pseudomonas aeruginosa isolates from children with cystic fibrosis on nebulised tobramycin – temporal relationship with antibiotic usage

Abstract number: 1733_1594

Doyle M., McNally P., Leen G., Dier J., Greally P., Murphy P.

Objectives: High level resistance (HLR) isolates of P. aeruginosa with a Minimum inhibitory concentration (MIC) >1024 for Tobramycin have been cultured from patients on Tobramycin Inhaled Solution (TSI). In the patients with isolates with an MIC > 1024 mg/mL, there is a tendency towards a more rapid fall off in both weight z scores and FEV1 [1].

The aim of this study is to explore the temporal relationship between use of (TSI) and fluctuations in the (MIC) in P. aeruginosa isolated from sputum of children with cystic fibrosis receiving inhaled Tobramycin.

Methods: Sputum was collected prospectively from all children with a persistent growth of P. aeruginosa receiving (TSI). Isolates were collected from Oct 2005 to Oct 2006. Patients were requested to send sputum for culture before and after a course of TSI therapy. All isolates were tested to evaluate the MIC. The timing and duration of TSI usage was recorded prospectively. The data was examined to establish if a temporal relationship exists between use of TSI and the changes in Tobramycin MIC of the P. aeruginosa isolates cultured.

Results: Thirty patients were treated with TSI during the study period. Two-hundred and twenty isolates were tested. The Tobramycin MIC in P. aeruginosa isolates from each patient fluctuated during the study period. No relationship could be demonstrated between the Tobramycin MIC from the P. aeruginosa isolated and the timing of TSI. Ten of the patients had a high level resistant (HLR) strain of P. aeruginosa isolated with a Tobramycin MIC of >1024 mg/mL. Seven patients remained colonised with a HLR isolate. One patient discontinued therapy with TSI during the study period. This patient continued to culture P. aeruginosa with a Tobramycin MIC >1024 one year after discontinuing TSI.

Conclusions: Isolates of P aeruginosa cultured from patients on TSI have a fluctuating Tobramycin MIC. The fluctuations in MIC do not appear to be related to the timing of therapy with TSI. Once a patient is colonised with an isolate with high level resistance to Tobramycin, most will remain colonised (7/10). The isolation of HLR P aeruginosa didn't cease once TSI therapy was stopped.


[1] Longitudinal development of tobramycin resistance in Pseudomonas aeruginosa isolates from children with cystic fibrosis on nebulised tobramycin – effects on clinical outcomes. Doyle M, McNally P, Leen G, Dier J, Greally P, Murphy P. ECCMID, 2006.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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