The effect of antibiotics on the cell morphology of Legionella pneumophila.

Legionella pneumophila, in Buffered Yeast Extract broth, was treated for 5 h at 37 degrees C with rosaramicin, erythromycin, cefotaxime, dibekacin, penicillin, methicillin, cefoxitin, cephalothin, ticarcillin, carbenicillin or polymyxin B at near-MIC levels and above. Electronmicroscopy demonstrated morphological changes to the bacteria in some, but not all, of the antibiotic-treated suspensions. Penicillin, at 1000 micrograms/ml (40 X MIC) but not less, produced smooth bubble-like structures on cell surfaces; methicillin produced rough bubble-like structures at 100 micrograms/ml (MIC) but not at 1000 micrograms/ml. In each case, these structures resembled spheroplasts. Polymyxin B induced small-bleb formation on the bacterial cell surfaces at all concentrations tested (MIC-10 X MIC). The other eight antibiotics did not induce any morphological changes at any concentration tested.