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Infect Immun, April 1998, p. 1492-1499, Vol. 66, No. 4
Infectious Diseases
Laboratories,1
Division of Tissue
Pathology,2 Institute of Medical and Veterinary
Science, Adelaide, South Australia 5000, and
Microbial
Pathogenesis Unit, The University of Adelaide, Adelaide, South
Australia 5005,3 Australia
Received 30 July 1997/Returned for modification 17 October
1997/Accepted 30 December 1997
To understand the basis of pathogenesis by Legionella
longbeachae serogroup 1, the importance of the Mip protein in
this species was examined. Amino-terminal analysis of the purified,
cloned L. longbeachae serogroup 1 ATCC 33462 Mip protein
confirmed that the cloned gene protein was expressed and processed in
an Escherichia coli background. DNA sequence analysis of
plasmid pIMVS27, containing the entire L. longbeachae
serogroup 1 mip gene, revealed a high degree of homology to
the mip gene of Legionella pneumophila
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
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Copyright © 1998, American Society for Microbiology. All rights reserved.
Sequence Analysis of the mip Gene of the Soilborne
Pathogen Legionella longbeachae
10 and
35 promoter regions. Primers designed from the mip gene sequence obtained for
L. longbeachae serogroup 1 ATCC 33462 were used to
amplify the mip genes from L. longbeachae
serogroup 2 ATCC 33484 and an Australian clinical isolate of L. longbeachae serogroup 1 A5H5. The mip gene from A5H5
was 100% identical to the type strain sequence. The serogroup 2 strain
of L. longbeachae differed by 2 base pairs in third-codon positions. Allelic exchange mutagenesis was used to generate an isogenic mip mutant in ATCC 33462 and strain A5H5. The ATCC
mip mutant was unable to infect a strain of
Acanthamoebae sp. both in liquid and in a potting mix
coculture system, while the A5H5 mip mutant behaved in a
manner siilar to that of L. pneumophila serogroup 1, i.e., it displayed a reduced capacity to infect and multiply within Acanthamoebae. To determine if this
mutation resulted in reduced virulence in the guinea pig animal model,
the A5H5 mip 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
L. longbeachae serogroup 1 species and is required for full
virulence.
*
Corresponding author. Mailing address: P.O. Box 14, Rundle Mall, Adelaide, South Australia 5000, Australia. Phone: 618 8222 3274. Fax: 618 8222 3543. E-mail:
Robyn.Doyle{at}imvs.sa.gov.au.
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