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Open Access Research article

Atypical Listeria innocua strains possess an intact LIPI-3

Evelyn M Clayton1, Karen M Daly1, Caitriona M Guinane3, Colin Hill12*, Paul D Cotter23* and Paul R Ross23

Author Affiliations

1 Department of Microbiology, University College Cork, Cork, Ireland

2 Alimentary Pharmabiotic Centre, Cork, Ireland

3 Teagasc, Moorepark Food Research Centre, Fermoy, Co, Cork, Ireland

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BMC Microbiology 2014, 14:58  doi:10.1186/1471-2180-14-58

Published: 8 March 2014

Abstract

Background

Listeria monocytogenes is a food-borne pathogen which is the causative agent of listeriosis and can be divided into three evolutionary lineages I, II and III. While all strains possess the well established virulence factors associated with the Listeria pathogenicity island I (LIPI-1), lineage I strains also possess an additional pathogenicity island designated LIPI-3 which encodes listeriolysin S (LLS), a post-translationally modified cytolytic peptide. Up until now, this pathogenicity island has been identified exclusively in a subset of lineage I isolates of the pathogen Listeria monocytogenes.

Results

In total 64‚ÄČL. innocua strains were screened for the presence of LIPI-3. Here we report the identification of an intact LIPI-3 in 11 isolates of L. innocua and the remnants of the cluster in several others. Significantly, we can reveal that placing the L. innocua lls genes under the control of a constitutive promoter results in a haemolytic phenotype, confirming that the cluster is capable of encoding a functional haemolysin.

Conclusions

Although the presence of the LIPI-3 gene cluster is confined to lineage I isolates of L. monocytogenes, a corresponding gene cluster or its remnants have been identified in many L. innocua strains.