Affiliation:
1. Department of Microbiology and Immunology, The University of Michigan Medical School, Ann Arbor, Michigan
Abstract
ABSTRACT
While the majority of Legionnaire’s disease has been attributed to
Legionella pneumophila
,
Legionella micdadei
can cause a similar infection in immunocompromised people. Consistent with its epidemiological profile, the growth of
L. micdadei
in cultured macrophages is less robust than that of
L. pneumophila
. To identify those features of the
Legionella
spp. which are correlated to efficient growth in macrophages, two approaches were taken. First, a phenotypic analysis compared four clinical isolates of
L. micdadei
to one well-characterized strain of
L. pneumophila
. Seven traits previously correlated with the virulence of
L. pneumophila
were evaluated: infection and replication in cultured macrophages, evasion of phagosome-lysosome fusion, contact-dependent cytotoxicity, sodium sensitivity, osmotic resistance, and conjugal DNA transfer. By nearly every measure,
L. micdadei
appeared less virulent than
L. pneumophila
. The surprising exception was
L. micdadei
31B, which evaded lysosomes and replicated in macrophages as efficiently as
L. pneumophila
, despite lacking both contact-dependent cytopathicity and regulated sodium sensitivity. Second, in an attempt to identify virulence factors genetically, an
L. pneumophila
genomic library was screened for clones which conferred robust intracellular growth on
L. micdadei
. No such loci were isolated, consistent with the multiple phenotypic differences observed for the two species. Apparently,
L. pneumophila
and
L. micdadei
use distinct strategies to colonize alveolar macrophages, causing Legionnaire’s disease.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
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