This report investigates the genetic background of L. pneumophila, provides clues to the evolution and emergence of this pathogen, and describes the identification of a worldwide-distributed epidemic clone.
Legionnaire’s disease is characterized by severe pneumonia, afflicting the elderly and individuals with weakened immune responses in particular. While L. pneumophila, a genetically diverse species and one of many Legionella species, is common in natural and drinking water supplies, the majority of Legionnaire’s disease cases worldwide (approximately 84%) are caused by a single serogroup, L. pneumophila Sg1. Recent work has suggested that even though Sg1 is responsible for most clinical cases, this serogroup accounts for only about 30% of environmental Legionella.
As the prevalence of Sg1 in Legionnaire’s disease cases does not appear to be a result of environmental predominance, the frequent occurrence of Sg1 in disease is likely due to higher virulence. In this study, researchers led by Dr. Carmen Buchrieser of the Institut Pasteur conducted a comparative genomics analysis to gain insight into the basis for the higher virulence of Sg1. To compare Sg1 and other Legionella isolates, the researchers constructed DNA-arrays containing genes known to be variable in L. pneumophila strains, including a set of known and potential virulence genes. “We screened the gene content of 217 L. pneumophila strains and 32 other Legionella (non-pneumophila) strains that were isolated from humans and the environment,” describes Buchrieser. “We discovered core virulence- and eukaryotic-like genes are highly conserved, indicating strong selection pressures for their preservation.”
Importantly, a cluster of lipopolysaccharide (LPS) biosynthesis genes was found to be common in Sg1, even in different genetic backgrounds. This suggests that the gene cluster could be transferred horizontally between strains. “The LPS of Sg1 itself may confer to Sg1 strains the high prevalence in human disease,” explains Buchrieser. Variation in LPS, a component of the cell wall normally recognized by the innate immune system, could allow the bacteria to evade host immune responses.
Most significantly, this study identified a specific clone of Sg1 that is present in both sporadic cases and outbreaks worldwide. “The identification of this clone opens exciting possibilities of research to find out which genes contribute to improved interaction with the host, or to improved fitness in the environment, or to both,” describes Buchrieser.
Buchrieser cautions that there may be other genetic factors involved in the emergence of an epidemic strain. “Although the strains carrying this LPS cluster seem to be particularly adapted for causing human disease, additional genetic factors present in the genome may have allowed a particular clone of Sg1 to evolve within this highly diverse species.”
In addition to gaining insight into the genetic basis for L. pneumophila Sg1 virulence, Buchrieser suggests this work may lead to new methods of detection. “The findings of this comparative genomics approach will be invaluable for the development of novel tools to rapidly detect Legionella-associated risk factors in water distribution systems of hospitals and other potential sites for Legionella infection.”
Peggy Calicchia | EurekAlert!
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy