Related Experiment Video

Updated: Jun 4, 2026

Purification of Pathogen Vacuoles from Legionella-infected Phagocytes
09:25

Purification of Pathogen Vacuoles from Legionella-infected Phagocytes

Published on: June 19, 2012

12.4K

Rapid Icm/Dot T4SS Inactivation Prevents Resuscitation of Heat-Induced VBNC Legionella pneumophila by Amoebae

Camille Schmid1, Hubert Hilbi1

  • 1Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland.

Environmental Microbiology
|January 15, 2025
PubMed

Insights

Heat stress induces viable but non-culturable (VBNC) Legionella pneumophila, impairing its Type IV secretion system (T4SS) before VBNC state induction. This prevents resuscitation in amoebae and macrophages.

Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Stress Response

Background:

  • Legionella pneumophila causes Legionnaires' disease, utilizing the Icm/Dot Type IV secretion system (T4SS) for intracellular replication.
  • The pathogen forms 'viable but non-culturable' (VBNC) cells under stress, evading detection by standard methods.

Purpose of the Study:

  • To investigate the effects of heat stress on L. pneumophila's transition to the VBNC state.
  • To determine the impact of heat-induced VBNC state on bacterial resuscitation and T4SS function.
  • To explore the role of the Legionella quorum sensing (Lqs)-LvbR network in heat-induced VBNC formation.

Main Methods:

  • Exposure of L. pneumophila to various heat stress conditions (50°C, 55°C, 60°C).
  • Assessment of bacterial viability, metabolic activity, cell membrane integrity, and culturability.
  • Evaluation of phagocyte uptake, Legionella-containing vacuole (LCV) formation, and effector protein secretion.
  • Analysis of T4SS activity and the role of Lqs-LvbR network mutants (∆lvbR, ∆lqsR, ∆lqsA) in heat sensitivity.

Main Results:

  • L. pneumophila entered the VBNC state after heat exposure (e.g., 50°C for 30h), retaining metabolic activity and membrane integrity.
  • Heat-induced VBNC L. pneumophila failed to resuscitate in amoebae or macrophages.
  • Phagocyte uptake, LCV formation, and Icm/Dot-dependent effector secretion were impaired in VBNC cells.
  • The Icm/Dot T4SS was rapidly inactivated upon heat exposure (50°C for 3-5h), preceding VBNC induction.
  • Mutant strains (∆lvbR, ∆lqsR) exhibited increased heat sensitivity, while ∆lqsA showed reduced sensitivity, implicating the Lqs-LvbR network in VBNC induction.

Conclusions:

  • Heat stress rapidly inactivates the Icm/Dot T4SS in L. pneumophila before the VBNC state is fully established.
  • This premature T4SS inactivation significantly hinders the resuscitation of heat-stressed VBNC L. pneumophila within host cells.
  • The Lqs-LvbR network plays a crucial role in regulating the heat-induced VBNC state in L. pneumophila.
Keywords:
AcanthamoebaDictyosteliumLegionellaVBNCdormancymacrophagepersistencequorum sensingsecretion systemtemperature

More Related Videos

Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection12:30

Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection

Published on: November 22, 2013

40.3K
Applying Live Cell Imaging and Cryo-Electron Tomography to Resolve Spatiotemporal Features of the Legionella pneumophila Dot/Icm Secretion System09:12

Applying Live Cell Imaging and Cryo-Electron Tomography to Resolve Spatiotemporal Features of the Legionella pneumophila Dot/Icm Secretion System

Published on: March 10, 2020

6.9K

Related Concept Videos

Defense Against Bacterial Pathogens01:31

Defense Against Bacterial Pathogens

The human immune system is a complex network of cells, tissues, and organs that work together to defend the body against bacterial infections. It consists of various immune cells, each playing a specific role in the defense mechanism.
Phagocytes
Phagocytes are the frontline soldiers of the immune system. They include neutrophils and macrophages. Neutrophils are the most abundant type of white blood cell and are quickly mobilized to the site of infection. Macrophages are larger cells that patrol...
Pulmonary Tuberculosis IV01:26

Pulmonary Tuberculosis IV

Tuberculosis, more commonly referred to as TB, is an infectious disease stemming from Mycobacterium tuberculosis. While it primarily impacts the lungs, TB can also affect other body areas. Given its severity and global impact, timely and accurate diagnosis is crucial for controlling its spread and improving patient outcomes.
Several diagnostic approaches are used to detect TB. The conventional method is the Tuberculin Skin Test (TST), also known as the Mantoux test. However, this method has...
Regulation of Bacterial Virulence01:28

Regulation of Bacterial Virulence

Pathogenic bacteria employ a range of regulatory mechanisms to modulate the expression of virulence genes in response to environmental and host-derived signals. These mechanisms ensure that virulence factors are expressed only under favorable conditions, thereby optimizing infection and survival strategies.Mechanisms of Virulence RegulationKey regulatory strategies include:Two-Component Systems: These consist of a membrane-bound sensor kinase and a cytoplasmic response regulator. Environmental...
Bacterial Meningitis01:24

Bacterial Meningitis

Bacterial meningitis is a severe infectious disease involving inflammation of the meninges, the protective membranes surrounding the brain and spinal cord. It occurs when pathogenic bacteria cross the blood–brain barrier and enter the cerebrospinal fluid. Common causative organisms include Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae type b, Listeria monocytogenes, and Escherichia coli K1. The exact route of entry varies by pathogen and host condition.Routes of Entry...
Tuberculosis01:23

Tuberculosis

Tuberculosis (TB) remains a significant global health concern, primarily targeting the lungs and spreading through airborne transmission. Infection begins when aerosolized droplet nuclei, expelled by an individual with active TB, are inhaled by another person. These microscopic particles carry Mycobacterium tuberculosis, the causative agent of TB. Upon reaching the alveoli, the bacilli are engulfed by alveolar macrophages. However, due to their specialized lipid-rich cell wall, these pathogens...
Bacterial Meningitis II: Pathophysiology01:26

Bacterial Meningitis II: Pathophysiology

Bacterial meningitis typically begins when pathogens such as Neisseria meningitidis and Streptococcus pneumoniae colonize the nasopharynx and invade the bloodstream. This process is facilitated by bacterial virulence factors, such as polysaccharide capsules, which resist phagocytosis and complement-mediated killing. Less commonly, bacteria reach the central nervous system via contiguous spread from infections like otitis media or sinusitis, through congenital or acquired dural defects, or...