The ubiquitous nature of Listeria monocytogenes clones: a large-scale Multilocus Sequence Typing study

Area of Science:

• Microbiology
• Genomics
• Food Safety

Background:

• Listeria monocytogenes is a ubiquitous pathogen found in diverse environments.
• It poses a significant threat through foodborne transmission, causing severe illness in humans and animals.
• Understanding its population structure and host associations is crucial for public health.

Purpose of the Study:

• To investigate the association between Listeria monocytogenes clonal complexes (CCs) and their sources (environment vs. hosts).
• To analyze the population structure and evolutionary dynamics of L. monocytogenes using Multilocus Sequence Typing (MLST).

Main Methods:

• Multilocus Sequence Typing (MLST) was performed on approximately 2000 isolates of Listeria monocytogenes.
• Isolate sources, including environmental, food, animal, and human samples, were analyzed in conjunction with MLST data.

Main Results:

• The majority of L. monocytogenes CCs (72%) were not specific to a single source, being isolated from various environments, food, animals, and humans.
• The population structure is largely clonal, comprising four main lineages, with most CCs remaining stable over decades.
• A specific epidemic clone (CC101) showed a historical pattern of rarity, recent increase, and potential re-emergence.

Conclusions:

• Listeria monocytogenes exhibits broad host and environmental adaptability, with limited source specificity for most clonal complexes.
• The clonal population structure is stable, but dynamic shifts, like the re-emergence of CC101, highlight the need for ongoing surveillance.
• Historical analysis suggests that dominant sequence types within CCs arise from increased frequency rather than ancestral founding.