Y-019. Association of Multiple-Locus VNTR Clusters and Phage Type Lineages among Salmonella Enteritidis Isolates from Sporadic Human Cases in the United States

S. Cho¹, T. S. Whittam¹, D. J. Boxrud², J. M. Bartkus², S. C. Rankin³, M. J. Wilkins⁴, P. Somsel⁴, F. P. Downes⁴, L. D. Warnick⁵, M. Wiedmann⁵, A. M. Saeed¹;
¹Michigan State Univ., East Lansing, MI, ²Minnesota Dept. of Hlth., St. Paul, MN, ³Univ. of Pennsylvania, Philadelphia, PA, ⁴Michigan Dept. of Community Hlth., Lansing, MI, ⁵Cornell Univ., Ithaca, NY.

Background: Salmonella enterica serotype Enteritidis (S. Enteritidis) has emerged in the last three decades as the most common serotype in Europe and other parts of the world. Homogeneity of S. Enteritidis genome renders subtyping tools insufficient for molecular characterization and therefore, more efficient subtyping methods are required. Methods: S. Enteritidis isolates were systematically collected from sporadic cases of S. Enteritidis infections in Michigan (n=51), Minnesota (n=112), New York (n=58), and Washington (n=24) between 2000 and 2007. We performed Multiple-Locus Variable Number Tandem Repeat Analysis (MLVA) on all isolates that were phage typed at the CDC /or Univ. of Pennsylvania Salmonella Reference Center. Results: We identified 94 unique MLVA types and 22 different phage types (PT) among the 245 isolates. Nei’s diversity index of 9 VNTR loci markers ranged from 4.0 to 78.9 (Median: 50.3). Some specific phage types were found to be associated with a predominant allele for certain VNTR loci. For example, PT8, PT13a, and PT13 were significantly associated with a predominant allele (accounting for 55%) at locus SE1. Cluster analysis using minimum-spanning tree demonstrated 2 major clusters (I, II) and 1 minor cluster of isolates. Cluster I included 65 distinct MLVA types among 166 isolates. Cluster II included 21 unique MLVA types from 69 isolates. We found significant association between MLVA-based clusters and phage types: PT8, PT13a, PT13, and PT34 were significantly associated with MLVA cluster I while PT4, PT1, PT6a, and PT18 were significantly associated with MLVA cluster II. S. Enteritidis isolates from NY and MI were associated with MLVA-based cluster I, whereas isolates from MN were associated with cluster II. Conclusion: We demonstrated that specific phage types were associated with a predominant allele for certain VNTR loci. We found significant association between MLVA clusters and phage types. We conclude that diverse profiles of the VNTR loci can be correlated with specific phage type lineages and could serve as useful molecular markers for S. Enteritidis.