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Open Access Research article

CRISPR-MVLST subtyping of Salmonella enterica subsp. enterica serovars Typhimurium and Heidelberg and application in identifying outbreak isolates

Nikki Shariat1, Carol H Sandt2, Michael J DiMarzio1, Rodolphe Barrangou13 and Edward G Dudley1*

Author Affiliations

1 Department of Food Science, The Pennsylvania State University, University Park, PA 16802, USA

2 The Pennsylvania Department of Health, Bureau of Laboratories, Division of Clinical Microbiology, Exton, PA 19341, USA

3 Current address: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695, USA

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BMC Microbiology 2013, 13:254  doi:10.1186/1471-2180-13-254

Published: 12 November 2013

Abstract

Background

Salmonella enterica subsp. enterica serovars Typhimurium (S. Typhimurium) and Heidelberg (S. Heidelberg) are major causes of foodborne salmonellosis, accounting for a fifth of all annual salmonellosis cases in the United States. Rapid, efficient and accurate methods for identification are required for routine surveillance and to track specific strains during outbreaks. We used Pulsed-field Gel Electrophoresis (PFGE) and a recently developed molecular subtyping approach termed CRISPR-MVLST that exploits the hypervariable nature of virulence genes and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) to subtype clinical S. Typhimurium and S. Heidelberg isolates.

Results

We analyzed a broad set of 175 S. Heidelberg and S. Typhimurium isolates collected over a five-year period. We identified 21 Heidelberg Sequence Types (HSTs) and 37 Typhimurium STs (TSTs) that were represented by 27 and 45 PFGE pulsotypes, respectively, and determined the discriminatory power of each method.

Conclusions

For S. Heidelberg, our data shows that combined typing by both CRISPR-MVLST and PFGE provided a discriminatory power of 0.9213. Importantly, CRISPR-MVLST was able to separate common PFGE patterns such as JF6X01.0022 into distinct STs, thus providing significantly greater discriminatory power. Conversely, we show that subtyping by either CRISPR-MVLST or PFGE independently provides a sufficient discriminatory power (0.9345 and 0.9456, respectively) for S. Typhimurium. Additionally, using isolates from two S. Typhimurium outbreaks, we demonstrate that CRISPR-MVLST provides excellent epidemiologic concordance.

Keywords:
CRISPR subtyping; CRISPR-MVLST; Molecular subtyping; Salmonella Heidelberg; Salmonella Typhimurium