Physiological and Antigenic Characteristics of Virulent and Attenuated Strains of Legionella pneumophila (Philadelphia 3)

Abstract : Several methods were used to characterize selected virulent and attenuated strains of Legionella pneumophila serogroup 1. The cultural characteristics of these strains on solid and liquid media were similar except that The attenuated strain grew faster. Chemical analysis revealed no significant differences between virulent and attenuated strains, nor did comparisons with three other serogroups of Legionella reveal any dissimilarities. the attenuated strain was generally more sensitive to cell wall digestion by hydrolytic enzymes. The effect of trypsin and chymotrypsin demonstrated further differences between these strains. SDS-PAGE of whole cell preparations showed only a slight difference. Antiserum directed against the virulent form showed similar microagglutination titers when either the virulent or attenuated form was used as antigen. Soluble heat extracts of the two forms, when subjected to SDS-PAGE, revealed a large 200,000 MW peptide in the attenuated strain which was absent in the virulent strain. Results of immunoelectrophoresis experiments employing adsorbed and unadsorbed antisera also suggested a difference in cellular antigens between the two strains examined. (Author)