Open Access Highly Accessed Research article

Macrolides decrease the minimal inhibitory concentration of anti-pseudomonal agents against Pseudomonas aeruginosa from cystic fibrosis patients in biofilm

Larissa Lutz1, Dariane Castro Pereira1, Rodrigo Minuto Paiva2, Alexandre Prehn Zavascki3 and Afonso Luis Barth4*

Author Affiliations

1 Unidade de Microbiologia, Serviço de Patologia Clínica, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil

2 Unidade de Biologia Molecular, Serviço de Patologia Clínica, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil

3 Infectious-Diseases Service, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil

4 Serviço de Patologia Clínica, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil

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BMC Microbiology 2012, 12:196  doi:10.1186/1471-2180-12-196

Published: 8 September 2012

Abstract

Background

Biofilm production is an important mechanism for bacterial survival and its association with antimicrobial resistance represents a challenge for the patient treatment. In this study we evaluated the in vitro action of macrolides in combination with anti-pseudomonal agents on biofilm-grown Pseudomonas aeruginosa recovered from cystic fibrosis (CF) patients.

Results

A total of 64 isolates were analysed. The biofilm inhibitory concentration (BIC) results were consistently higher than those obtained by the conventional method, minimal inhibitory concentration, (MIC) for most anti-pseudomonal agents tested (ceftazidime: P = 0.001, tobramycin: P = 0.001, imipenem: P < 0.001, meropenem: P = 0.005). When macrolides were associated with the anti-pseudomonal agents, the BIC values were reduced significantly for ceftazidime (P < 0.001) and tobramycin (P < 0.001), regardless the concentration of macrolides. Strong inhibitory quotient was observed when azithromycin at 8 mg/L was associated with all anti-pseudomonal agents tested in biofilm conditions.

Conclusions

P. aeruginosa from CF patients within biofilms are highly resistant to antibiotics but macrolides proved to augment the in vitro activity of anti-pseudomonal agents.

Keywords:
Antimicrobial susceptibility test; Biofilm; Azithromycin; Clarithromycin