Intrinsic drug resistance of M. aviumM. intracellulare complex: the role played by efflux pumps

Abstract number: P1818

Rodrigues L., Wagner D., Viveiros M., Sampaio D., Martins M., Couto I., Vavra M., Kern W., Amaral L.

Objectives: The Mycobacterium aviumM. intracellulare complex (MAC) accounts for the nontuberculous mycobacteria most frequently found in clinical specimens, especially in AIDS patients in industrialised countries. Treatment of infections caused by MAC is problematic due to its intrinsic resistance to antibiotics. Although efflux pumps (EPs) have been shown to be of clinical relevance in other bacteria, the importance of drug efflux in mycobacteria is not yet fully understood. In this work, we have characterised the EPs activity in ten MAC clinical strains through an automated fluorometric method and correlated it with intrinsic resistance to antibiotics.

Methods: Two MAC reference strains (M. avium ATCC25291T and M. intracellulare ATCC13950T) and ten clinical strains isolated from AIDS patients were evaluated for accumulation and efflux of ethidium bromide (EtBr) in the presence or absence of the EPs inhibitors (EPIs) thioridazine (TZ), chlorpromazine (CPZ), verapamil (VP) and the proton uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). For this purpose, an automated real-time fluorometric method that separately assesses accumulation and extrusion of EtBr was used. The effect of the above agents on the MICs of several antibiotics was determined by the broth microdilution method (CLSI).

Results: The automated real-time fluorometric method allowed the detection and quantification of EtBr transport across MAC cell wall. Accumulation of EtBr inside the cell was found to be temperature-dependent and significantly increased by the EPIs TZ, CPZ, CCCP and VP, at half their MICs. The removal of these agents from the medium resulted in energy dependent efflux of EtBr. EPIs promoted the reduction of MICs of MAC strains towards clarithromycin, erythromycin, ethambutol and to a minor extent, rifampicin and amikacin.

Conclusion: The results presented in this work are the first clear evidence of the role played by EPs in the intrinsic resistance of MAC to drugs. In particular, we were able to demonstrate active efflux contribution to intrinsic drug resistance in ten clinical MAC strains isolated from AIDS patients. Furthermore, we found that MAC intrinsic resistance to antibiotics is affected by EPIs such as TZ or CPZ, an effect that might be important in research and development of new and more effective antimycobacterial therapies.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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