The effect of antibiotics that inhibit cell-wall, protein, and DNA synthesis on the growth and morphology of Legionella pneumophila.

The response of Legionella pneumophila to antibiotics that inhibit cell-wall, protein and DNA synthesis was examined by electronmicroscopy, MIC estimations and viable counts. Ampicillin, cefotaxime, methicillin, erythromycin, rifampicin and ciprofloxacin, each used separately at 20 times their respective MIC values, showed activity against L. pneumophila in these studies. The inhibitors of cell-wall synthesis--ampicillin, cefotaxime and methicillin--effected the greatest bactericidal activity and induced the most extensive morphological changes, which included the formation of membranous lesions through which cytoplasmic contents were lost. In terms of ultrastructural damage and loss of viability, the inhibitors of protein and DNA synthesis were less effective than the antibiotics that acted on the microbial cell wall. Erythromycin- and rifampicin-treated cells possessed irregular membranes and were partially or fully lysed, whereas ciprofloxacin induced abnormally elongated organisms with intermittently lysed and detached inner membranes. These results illustrated the ability of antibiotics of putative clinical value, with diverse modes of action, to affect the ultrastructural cytology as well as the viability of L. pneumophila in vitro.