Phenotype versus genotype of the 19 kD peptido-glycan associated protein of Legionella (PpIA), among Legionellae and other gram-negative bacteria.

The protein PpIA (19 kD) cloned from a genomic library of Legionella pneumophila, Philadelphia 1, represents a peptido-glycan associated outer membrane protein in recombinant E. coli K-12 and L. pneumophila. It exhibits distinct sequence homology to lipoproteins of Haemophilus influenzae and E. coli. A ppIA specific DNA probe generated by PCR was used in Southern hybridizations of chromosomal DNA of Legionella strains and other Gram-negative pathogens. Under conditions of high stringency, hybridization could only be observed in L. pneumophila isolates, but all other Legionella strains tested displayed hybridization under lower stringency. No signals appeared after hybridization of chromosomal DNA from a variety of other bacteria. Using anti-PpIA monospecific polyclonal antibodies in Western blots, it was demonstrated that PpIA related proteins of nearly the same size are found in all L. pneumophila isolates and in a variety of, but not all, the Legionella species analysed here.