DescriptionPathogenicity for humans
Legionellae were first detected in 1976 after a particularly notable outbreak of pneumonia in a hotel
on the occasion of a United States army veterans’ meeting (Fraser et al., 1977). Since that time, it
has been established that these organ-isms are an important cause of pneumonia, both
community-acquired (1–15%) (Lieberman et al., 1996; Butler & Breiman, 1998) and hospitalacquired
(up to 50%) (Butler & Breiman, 1998). To date, disease due to Legionella has been
detected almost exclusively in humans, but some animals (e.g. guinea-pigs, rats, mice, marmosets,
and monkeys) are susceptible to experimental infection. One case of Legionella pneumonia has
also been reported in a calf......
Species of the genus Legionella are Gram-negative, non-spore-forming, rod-shaped, aerobic
bacteria. They contain branched-chain fatty acids, have a non-fermentative metabolism, and
require L-cysteine and iron salts for growth. They have been placed in the family Legionellaceae,
which contains the single genus Legionella; there are at least 42 species, which are listed in Table
5 (Drozanski, 1991; Adeleke et al., 1996; Hookey et al., 1996; Fry & Harrison, 1998; Riffard et al.,
1998). The type species is L. pneumophila. Two other genera have been proposed but have not
received general recognition (Garrity, Brown & Vickers, 1980): Fluoribacter for the blue-white
fluorescing species such as L. bozemanii and L. dumoffii, and Tatlockia for the species L.
micdadei. Some species of Legionella can be further differentiated into serotypes, of which there
are at least 15 for L. pneumophila but so far no more than two for any other specieS
Legionella: Molecular Microbiology Legionella pneumophila is a ubiquitous intracellular bacterium found widely in the
environment and is the cause of sporadic outbursts of opportunistic infection, mainly in immunocompromised individuals, including young children as well as aged persons.
The host response to this organism is similar to responses to other opportunistic intracellular microbes and features both innate and adoptive immune mechanisms. Innate immunity includes the responses of a variety of host cells and cytokines, including those produced by macrophages stimulated by microbial antigens. Adoptive immunity consists of activated lymphocytes and the cytokines they produce, such as interferon and other cytokines that activate macrophages to restrict the growth and spread of intracellular bacteria. The role of cytokines specifically in resistance and immunity to Legionella is exemplified by studies concerning the nature and mechanism whereby interferon produced by activated T lymphocytes influences macrophages to resist infection by this bacterium, not only by restricting growth but also killing this bacterium. This cytokine is considered to have a key role in activating macrophages in adoptive immunity to Legionella and other intracellular bacteria. In particular, interferon is known to have a crucial role in activating macrophages to resist infection by L. pneumophila. This review also describes newer findings that demonstrate that various cytokines that define Th1 vs Th2 helper cell activity also are important in regulating resistance versus susceptibility to this ubiquitous microorganism.
Legionellosis is a disease of significant medical and public interest.
Legionella is commonly found in aquatic habitats where its ability to survive and to multiply within different protozoa equips the bacterium to be transmissible and pathogenic to humans. In addition, Legionella has become a favored model system to analyze the mechanisms of bacterial survival, acquisition of nutrients, and intracellular replication. Following the recent publication of the genome sequences of four L. pneumophila strains, it is now feasible to investigate the whole genome in silico, the transcriptome via micro arrays, and the proteome by two-dimensional gel electrophoresis. Research in the fields of clinical features, diagnosis, treatment, and epidemiology continues to generate new data. The topics covered by this volume range from the history of the identification of Legionella and clinical disease treatment, to the microbe's gene expression and secretion systems, as well as its strategies for intracellular multiplication and nutrient acquisition. The main focus of the book is the current state of many of the most critical features of Legionella. Internationally renowned authors have contributed chapters describing and discussing the latest research findings with an emphasis on molecular aspects. The editors and authors have produced an excellent book that will be an extremely useful reference source. This comprehensive publication is aimed at readers with teaching or research interests in microbiology, genetics, genomics, infectious diseases, or clinical MORONS NUM INSTIPUTO QUALQUER