TABLE 1.

Description of L. monocytogenes isolate sets used for this study

Isolate set no.	Description	Purpose and use of isolate seta
1	36 food isolates representing all 36 EcoRI ribotypes found among food isolates collected in the United States, as described by Gray et al. (6)	Isolates were screened by sequencing an ∼1,600-bp 3′ fragment of inlA to identify premature stop codon mutations associated with food isolates
2	58 isolates representing L. monocytogenes EcoRI ribotypes commonly detected in feces from healthy ruminants, selected from a previously described collection of 108 L. monocytogenes fecal isolates from healthy ruminants (25)	Isolates were screened by sequencing an ∼1,600-bp 3′ fragment of inlA to identify premature stop codon mutations associated with isolates from healthy cattle
3	62 ribotype DUP-1062A isolates, representing all available DUP-1062A isolates from human listeriosis infections (n = 12), and 50 DUP-1062A food isolates selected from the 151 DUP-1062A food isolates described by Gray et al. (6) to represent a variety of different ready-to-eat foods	Isolates were screened by PCR-RFLP to identify the presence of premature stop codon mutation type 3; all DUP-1062A isolates characterized by serotyping (n = 11) were serotype 1/2a
4	54 ribotype DUP-1052A isolates, representing all 30 DUP-1052A isolates from human listeriosis infections that were not previously characterized and 24 food isolates selected from the 58 DUP-1052A food isolates described by Gray et al. (6) to represent a variety of different ready-to-eat foods	Isolates were screened by sequencing an ∼800-bp 3′ fragment of inlA to identify the presence of premature stop codon mutation type 1; all DUP-1052A isolates characterized by serotyping (n = 10) were serotype 1/2b
5	Eight ribotype DUP-1025A isolates, representing all four DUP-1025A isolates from human listeriosis infections that were not previously characterized and selected food isolates (n = 4)	Isolates were screened by sequencing an ∼800-bp 3′ fragment of inlA to identify the presence of premature stop codon mutation type 2; all DUP-1025A isolates characterized by serotyping (n = 9) were serotype 1/2b
6	All DUP-16635A isolates from foods (n = 4) that were not previously characterized	Isolates were screened by sequencing an ∼800-bp 3′ fragment of inlA to identify the presence of premature stop codon mutation type 1; all DUP-16635A isolates (n = 5) were serotype 1/2b

^aThe number of isolates characterized by serotyping included 8 DUP-1052A, 2 DUP-1025A, 1 DUP-1031A, 3 DUP-1062A, and 2 DUP-1046B isolates serotyped by Nightingale et al. (24) as well as 24 isolates that were not previously reported.