Multilocus sequence typing of outbreak-associated XXXX isolates to identify epidemic clones.

@entity1 @entity5599 @entity28620 @entity5125 @entity14821
OBJECTIVE: @entity5125 is a foodborne pathogen found in a wide variety of environments. Subtype characterization of @entity5125 isolates from listeriosis outbreaks that have occurred over the last three decades has suggested that a number of outbreaks were caused by a small number of @entity5125 epidemic clones (ECs). In this study we compared the prevalence, ecology, and phylogenetic position of outbreak-associated isolates and non-outbreak-associated isolates to probe the evolutionary and ecological characteristics of outbreak-associated @entity5125 subtypes, including those representing previously described ECs. METHODS: Multilocus sequence typing data for isolates from 15 listeriosis outbreaks in Europe and North America were generated and compared, using a phylogenetic framework, with 180 isolates representing a local sampling of diverse sources, including @entity1 sporadic cases. RESULTS: Isolates from 15 listeriosis outbreaks represented eight @entity5599 ( @entity5599 ). @entity5599 corresponding to previously designated ECI ( @entity28620 and @entity14821 ) and ECIa (ST29) represented isolates from eight outbreaks. ST17 (corresponding to ECII) was involved in two outbreaks in the United States (1998 and 2002). No other @entity5599 were involved in multiple outbreaks. While @entity28620 was the most common ST among sporadic @entity1 cases and non- @entity1 listeriosis-related isolates, ST29 was rare among non- @entity1 listeriosis-related isolates and was significantly overrepresented among isolates from @entity1 listeriosis outbreaks and sporadic cases as compared to isolates from other sources in our local sampling. CONCLUSIONS: @entity5599 associated with outbreaks (and representing previously designated ECs) appear to differ in their ecology. While association of ECI with multiple @entity1 listeriosis outbreaks appears to reflect strain abundance across environments, ECIa seems to represent an @entity5125 EC that appears to be overrepresented among outbreaks and sporadic cases and thus may have increased transmission potential.
