Legionella pneumophila: The Journey from the Environment to the Blood

Abstract

An outbreak of a potentially fatal form of pneumonia in 1976 and in the annual convention of the American Legion was the first time that Legionella spp. was identified. Thereafter, the term Legionnaires’ disease (LD) was established. The infection in humans is transmitted by the inhalation of aerosols that contain the microorganisms that belong to the Legionellaceae family and the genus Legionella. The genus Legionella contains genetically heterogeneous species and serogroups. The Legionella pneumophila serogroup 1 (Lp1) is the most often detected strain in outbreaks of LD. The pathogenesis of LD infection initiates with the attachment of the bacterial cells to the host cells, and subsequent intracellular replication. Following invasion, Legionella spp. activates its virulence mechanisms: generation of specific compartments of Legionella-containing vacuole (LCV), and expression of genes that encode a type IV secretion system (T4SS) for the translocation of proteins. The ability of L. pneumophila to transmigrate across the lung’s epithelium barrier leads to bacteremia, spread, and invasion of many organs with subsequent manifestations, complications, and septic shock. The clinical manifestations of LD depend on the bacterial load in the aerosol, the virulence factors, and the immune status of the patient. The infection has two distinct forms: the non- pneumatic form or Pontiac fever, which is a milder febrile flu-like illness, and LD, a more severe form, which includes pneumonia. In addition, the extrapulmonary involvement of LD can include heart, brain, abdomen, and joints.

Legionella-Induced Hepatitis: A Case Report

“…While the most common extrapulmonary manifestation is usually in the myocardium, there have also been reports of pyelonephritis and pancreatitis [11,12]. Legionella's seemingly variable extrapulmonary and multisystem involvement can be attributed to the organism's ability to cross the lung epithelium, resulting in bacteremia and multi-system effects [13]. This explanation of Legionella's effects on various organ systems is further corroborated by Watts et al (1980), who conducted a post-mortem analysis of an immunocompromised patient who succumbed to acute pneumonia caused by Legionnaires'.…”

Long‐term monitoring of the microbial quality and Legionnaires' disease risk in tap water from mass catering establishments

“…The most used medium for the growth of Legionella spp. is buffered charcoal yeast extract (BCYE) agar, which is composed of a base derived from CYE agar providing the optimal pH (pH 6.9) (Iliadi et al, 2022). Legionella spp.…”

“…Two basic mechanisms have been proposed for aquatic L. pneumophila to reach the lungs: (1) the bacteria settles in the upper respiratory system and reaches the lungs by aspiration, or (2) the water droplets (aerosols) hanging in the air cause this bacteria to reach the lungs through respiration (Moumanis et al, 2021). L. pneumophila can proliferate in standing water at temperatures between 20 C and 45 C (Mentula et al, 2023), but there is no significant difference in growth at 46 C (Iliadi et al, 2022).…”

Whole-genome sequencing of the clinical isolate of Legionella pneumophila ALAW1 from the West Bank allows high-resolution typing and determination of pathogenicity mechanisms

“…Studies on this ubiquitous water-based pathogen should be directed towards both sides: i) the clinical side from pneumonia patients, and ii) the environmental side from DWDS of hospitals and public buildings [ 16 ]. The problem is apparent in the West Bank because awareness about the prevalence of L. pneumophila or LD is lacking, and data scarcity for such arid regions.…”