“Epidemic Clones” of Listeria monocytogenes Are Widespread and Ancient Clonal Groups

Abstract

The food-borne pathogen Listeria monocytogenes is genetically heterogeneous. Although some clonal groups have been implicated in multiple outbreaks, there is currently no consensus on how "epidemic clones" should be defined. The objectives of this work were to compare the patterns of sequence diversity on two sets of genes that have been widely used to define L. monocytogenes clonal groups: multilocus sequence typing (MLST) and multi-virulence-locus sequence typing (MvLST). Further, we evaluated the diversity within clonal groups by pulsed-field gel electrophoresis (PFGE). Based on 125 isolates of diverse temporal, geographical, and source origins, MLST and MvLST genes (i) had similar patterns of sequence polymorphisms, recombination, and selection, (ii) provided concordant phylogenetic clustering, and (iii) had similar discriminatory power, which was not improved when we combined both data sets. Inclusion of representative strains of previous outbreaks demonstrated the correspondence of epidemic clones with previously recognized MLST clonal complexes. PFGE analysis demonstrated heterogeneity within major clones, most of which were isolated decades before their involvement in outbreaks. We conclude that the "epidemic clone" denominations represent a redundant but largely incomplete nomenclature system for MLST-defined clones, which must be regarded as successful genetic groups that are widely distributed across time and space.

Clonogrouping, a Rapid Multiplex PCR Method for Identification of Major Clones of Listeria monocytogenes

“…Among these, 185 were analyzed previously by MLST (6,7,15), whereas the MLST genotypes of the 97 remaining strains were determined in the present study. The latter strains were selected from the Collection of Listeria of the Institut Pasteur (CLIP) maintained at the French National Reference Centre and the WHO Collaborating Centre for Listeria.…”

“…The large-scale application of MLST led to the identification of numerically predominant and internationally widespread clonal complexes (CCs), which are considered clones, i.e., sets of isolates descending from a single common ancestor (5-9). Most major clones have been involved in outbreaks of listeriosis (7,(10)(11)(12). Rapid identification of MLST clones is important for epidemiological surveillance and outbreak investigation.…”

“…Clonal complexes were defined as groups of allelic profiles sharing at least 6 of 7 alleles with at least one other member of the group (5). Allelic profiles sharing less than 6 alleles with all other allelic profiles were designated singletons; these groups were defined based on MLST data from this study and previous studies (5)(6)(7)(8)15). The discrimination index was calculated using an online tool (http://darwin.phyloviz.net/Comparing Partitions).…”

Listeria monocytogenes Associated with New Zealand Seafood Production and Clinical Cases: Unique Sequence Types, Truncated InlA, and Attenuated Invasiveness

“…The higher level of sequence polymorphisms associated with MVLST has enabled local epidemiological studies, often differentiating outbreak and epidemic strains from other isolates (17,18). Cantinelli et al (19), however, recently compared 125 L. monocytogenes strains and found that MVLST and MLST provided similar sequence types (STs), phylogenetic clustering, and discriminatory power. Mutations in virulence genes are associated with a reduced invasion phenotype in L. monocytogenes.…”

Emergence and Prevalence of Non-H 2 S-Producing Salmonella enterica Serovar Senftenberg Isolates Belonging to Novel Sequence Type 1751 in China

“…To our knowledge, this is the first report of non-H 2 S-producing S. Senftenberg bacteria in the world. In this study, the microbiological and genetic characteristics of the non-H 2 S-producing and selected H 2 S-producing S. Senftenberg isolates were determined using a biphasic approach consisting of phenotypic (biochemical, serological, and antimicrobial susceptibility) and molecular (pulsed-field gel electrophoresis [PFGE], multilocus sequence typing [MLST], and clustered regularly interspaced short palindromic repeat [CRISPR]) analysis (15)(16)(17)(18)(19). The molecular mechanism behind the lack of H 2 S production was also explored.…”