GENTAMICIN-CONTAINING PEPTONE-YEAST EXTRACT MEDIUM FOR COCULTIVATION OF HARTMANNELLA-VERMIFORMIS ATCC-50256 AND VIRULENT-STRAINS OF LEGIONELLA-PNEUMOPHILA

We Evaluated the use of peptone-yeast extract (PY) medium, different s trains of Hartmanella vermiformis, and gentamicin in a coculture syste m to improve the discrimination of virulent and avirulent strains of L egionella pneumophila. H. vermiformis ATCC 50256 was unique among four strains of H. vermiformis in that it multiplied equally well in Mediu m 1034 and PY medium (Medium 1034 without fetal calf serum, folic acid , hemin, apd yeast nucleic acid and with a 50% reduction of peptone), However, both a virulent strain of L. pneumophila and its avirulent de rivative strain multiplied in cocultures when PY medium was used. The multiplication of this avirulent strain was greatly reduced by incorpo rating gentamicin (1 mu g/ml) into the cocultivation system. Five viru lent-avirulent sets of L. pneumophila strains were then tested for mul tiplication in cocultures with H. vermiformis ATCC 50256 and the genta micin-containing PY medium. Only the virulent strains multiplied. The modified cocultivation system can discriminate between virulent and av irulent strains of L. pneumophila.