Insertion sequences as highly resolutive genomic markers for sequence type 1 Legionella pneumophila Paris
Mike Vergnes1, Christophe Ginevra, Elisabeth Kay
1Laboratoire Adaptation et Pathogénie des Microorganismes, Université Joseph Fourier, 38042 Grenoble Cedex 9, France.
Abstract:
The causative agent of legionellosis, Legionella pneumophila, colonizes all natural and human-made water networks, thus constituting the source of contaminated aerosols responsible for airborne human infections. Efficient control of infections, especially during epidemics, necessitates the fastest and most resolutive identification possible of the bacterial source for subsequent disinfection of reservoirs. We thus compared recognized typing approaches for Legionella with a method based on characterization of insertion sequence (IS) content. A total of 86 clinical or environmental isolates of L. pneumophila, including 84 Paris isolates, sampled from 25 clinical investigations in France between 2001 and 2007, were obtained from the Legionella National Reference Center. All strains were typed by monoclonal antibody subgrouping, sequence-based typing, pulsed-field gel electrophoresis, and restriction fragment length polymorphism based on the presence or absence of IS elements. We identified six different types of IS elements in L. pneumophila Paris and used them as genomic markers in hybridization experiments. One IS type, ISLpn11, revealed a high discriminatory power. Simpson's index of discrimination, calculated from the distribution of IS elements, was higher than that obtained with the other typing methods used for L. pneumophila Paris. Moreover, specific ISLpn11 copies were found only in strains isolated from particular cities. In more than half of the cases, each clinical isolate had an ISLpn11 profile that was recovered in at least one environmental isolate from the same geographical location, suggesting that our method could identify the infection source. Phylogenetic analysis suggests a clonal expansion for the L. pneumophila Paris strain.
Insights
Identifying the source of Legionella pneumophila infections is crucial for controlling outbreaks. A new method using insertion sequence (IS) elements, particularly ISLpn11, proved highly effective in pinpointing bacterial sources from environmental and clinical samples.
Area of Science:
- Microbiology
- Epidemiology
- Genomics
Background:
- Legionella pneumophila causes legionellosis, spreading through water systems via contaminated aerosols.
- Rapid identification of infection sources is vital for controlling Legionnaires' disease outbreaks and disinfecting reservoirs.
Purpose of the Study:
- To compare established Legionella typing methods with a novel approach based on insertion sequence (IS) content characterization.
- To evaluate the discriminatory power of IS elements for identifying L. pneumophila sources.
Main Methods:
- Typing of 86 L. pneumophila isolates (clinical and environmental) using monoclonal antibody subgrouping, sequence-based typing, pulsed-field gel electrophoresis, and IS element profiling.
- Characterization of six IS element types in L. pneumophila Paris, with a focus on ISLpn11 for genomic marker analysis.
Main Results:
- ISLpn11 demonstrated superior discriminatory power compared to other typing methods for L. pneumophila Paris.
- Specific ISLpn11 profiles were linked to particular cities, and over half of clinical isolates matched environmental isolates from the same location.
- Phylogenetic analysis indicated clonal expansion within the L. pneumophila Paris strain.
Conclusions:
- Insertion sequence (IS) element profiling, especially using ISLpn11, is a powerful tool for identifying the sources of Legionella pneumophila infections.
- This method facilitates rapid source tracking, crucial for effective outbreak management and disinfection strategies.
