Activity of amoxycillin-clavulanic acid against Legionella pneumophila in vitro and in an experimental respiratory infection model.

Amoxycillin and clavulanic acid show good activity against Legionella pneumophila in vitro, and synergy has been observed between the two agents. However, in tissue culture studies, amoxycillin was inactive against intracellular legionellae, whereas clavulanic acid and amoxycillin plus clavulanic acid were as effective as erythromycin in preventing bacterial growth. These latter findings were reflected in the results of therapy of a L. pneumophila pneumonia in the neutropenic rat. Amoxycillin was ineffective in reducing bacterial counts in the lungs of infected animals, but clavulanic acid and amoxycillin-clavulanic acid produced bactericidal effects similar to those of erythromycin. The data illustrate the bactericidal activity of amoxycillin-clavulanic acid and clavulanic acid against intracellular L. pneumophila in contrast to the lack of activity of amoxycillin.