Beschreibung:
<jats:title>ABSTRACT</jats:title>
<jats:p>
To understand the basis of pathogenesis by
<jats:italic>Legionella longbeachae</jats:italic>
serogroup 1, the importance of the Mip protein in this species was examined. Amino-terminal analysis of the purified, cloned
<jats:italic>L. longbeachae</jats:italic>
serogroup 1 ATCC 33462 Mip protein confirmed that the cloned gene protein was expressed and processed in an
<jats:italic>Escherichia coli</jats:italic>
background. DNA sequence analysis of plasmid pIMVS27, containing the entire
<jats:italic>L. longbeachae</jats:italic>
serogroup 1
<jats:italic>mip</jats:italic>
gene, revealed a high degree of homology to the
<jats:italic>mip</jats:italic>
gene of
<jats:italic>Legionella pneumophila</jats:italic>
serogroup 1, 76% homology at the DNA level and 87% identity at the amino acid level. Primer extension analysis determined that the start site of transcription was the same for both species, with some differences observed for the −10 and −35 promoter regions. Primers designed from the
<jats:italic>mip</jats:italic>
gene sequence obtained for
<jats:italic>L. longbeachae</jats:italic>
serogroup 1 ATCC 33462 were used to amplify the
<jats:italic>mip</jats:italic>
genes from
<jats:italic>L. longbeachae</jats:italic>
serogroup 2 ATCC 33484 and an Australian clinical isolate of
<jats:italic>L. longbeachae</jats:italic>
serogroup 1 A5H5. The
<jats:italic>mip</jats:italic>
gene from A5H5 was 100% identical to the type strain sequence. The serogroup 2 strain of
<jats:italic>L. longbeachae</jats:italic>
differed by 2 base pairs in third-codon positions. Allelic exchange mutagenesis was used to generate an isogenic
<jats:italic>mip</jats:italic>
mutant in ATCC 33462 and strain A5H5. The ATCC
<jats:italic>mip</jats:italic>
mutant was unable to infect a strain of
<jats:italic>Acanthamoebae</jats:italic>
sp. both in liquid and in a potting mix coculture system, while the A5H5
<jats:italic>mip</jats:italic>
mutant behaved in a manner siilar to that of
<jats:italic>L. pneumophila</jats:italic>
serogroup 1, i.e., it displayed a reduced capacity to infect and multiply within
<jats:italic>Acanthamoebae</jats:italic>
. To determine if this mutation resulted in reduced virulence in the guinea pig animal model, the A5H5
<jats:italic>mip</jats:italic>
mutant and its parent strain were assessed for their abilities to establish an infection after aerosol exposure. Unlike the virulent parent strain, the mutant strain did not kill any animals under two different dose regimes. The data indicate that the Mip protein plays an important role in the intracellular life cycle of
<jats:italic>L. longbeachae</jats:italic>
serogroup 1 species and is required for full virulence.
</jats:p>