Genetic markers unique to Listeria monocytogenes serotype 4b differentiate epidemic clone II (hot dog outbreak strains) from other lineages.
A small number of closely related strains of Listeria monocytogenes serotype 4b, designated epidemic clone I (ECI), have been implicated in numerous outbreaks of food-borne listeriosis described during the past two decades in Europe and North America. In 1998 to 1999, a multistate outbreak traced to contaminated hot dogs involved a different strain type of serotype 4b, with genetic fingerprints rarely encountered before. In spite of the profound economic and public health impact of this outbreak, the implicated bacteria (designated epidemic clone II [ECII]) have remained poorly characterized genetically, and nucleotide sequences specific for these strains have not been reported. Using genome sequence information, PCR, and Southern blots, we identified DNA fragments which appeared to be either absent or markedly divergent in the hot dog outbreak strains but conserved among other serotype 4b strains. PCR with primers derived from these fragments as well as Southern blots with the amplicons as probes readily differentiated ECII from other serotype 4b strains. The serotype 4b-specific region harboring these fragments was adjacent to inlA, which encodes a well-characterized virulence determinant. The findings suggest that ECII strains have undergone divergence in portions of a serotype-specific region that is conserved in other serotype 4b strains. Although the mechanisms that drive this divergence remain to be identified, DNA-based tools from this region can facilitate the detection and further characterization of strains belonging to this lineage.
Evans
Matthew R
MR
Department of Food Science, North Carolina State University, Raleigh, North Carolina 27695, USA.
Swaminathan
Bala
B
Graves
Lewis M
LM
Altermann
Eric
E
Klaenhammer
Todd R
TR
Fink
Ryan C
RC
Kernodle
Sheri
S
Kathariou
Sophia
S
D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004196:Disease Outbreaks; D005060:Europe / Q000453:epidemiology; D005516:Food Microbiology; D005517:Foodborne Diseases / Q000453:epidemiology / Q000382:microbiology; D005798:Genes, Bacterial; D005819:Genetic Markers; D006801:Humans; D008089:Listeria monocytogenes / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D008461:Meat Products / Q000382:microbiology*; D009656:North America / Q000453:epidemiology; D016133:Polymerase Chain Reaction; D012703:Serotyping
D017931:DNA Primers; D004269:DNA, Bacterial; D005819:Genetic Markers