[Evaluation of the extra- and intracellular activity of clarithromycin against Mycobacterium chelonae]

The in vitro activity of clarithromycin alone and in combination with amikacin, ethambutol and rifabutin was tested against twelve strains of M. chelonae abscessus and eight strains of M. chelonae chelonae isolated from patients. Extracellular activity of clarithromycin was assessed by determining MICs using the 1 p. cent proportion method in Middlebrook 7H11 agar media compared to the radiometric methodology in 7H12 broth at two pHs 6.8 and 7.4. The MICs obtained at pH 7.4 were 2 to 4 more dilutions lower than those obtained at pH 6.8. By both methods, clarithromycin appeared more active against isolates of M. chelonae chelonae than against isolates of M. chelonae abscessus. Clarithromycin- amikacin combination demonstrated the most important additive effect. The use of three drugs in association resulted in syngergistic effect. Studies of intracellular bacteria showed that the most effective bactericidal combination was clarithromycin amikacin and ethambutol together.