Affiliation:
1. Center for Biologics Evaluation and Research, Food and Drug Administration, Kensington, Maryland 20895
2. Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, Maryland 20740-3835
Abstract
ABSTRACT
We found seven
Listeria
isolates, initially identified as isolates with the Xyl
+
Rha
−
biotype of
Listeria welshimeri
by phenotypic tests, which exhibited discrepant genotypic properties in a well-validated
Listeria
species identification oligonucleotide microarray. The microarray gives results of these seven isolates being atypical
hly
-negative
L. seeligeri
isolates, not
L. welshimeri
isolates. The aberrant
L. seeligeri
isolates were
d
-xylose fermentation positive,
l
-rhamnose fermentation negative (Xyl
+
Rha
−
), and nonhemolytic on blood agar and in the CAMP test with both
Staphylococcus aureus
(S
−
reaction) and
Rhodococcus equi
(R
−
reaction). All genes of the
prfA
cluster of
L. seeligeri
, located in the
prs-ldh
region, including the
orfA2
,
orfD
,
prfA
,
orfE
,
plcA
,
hly
,
orfK
,
mpl
,
actA
,
dplcB
,
plcB
,
orfH
,
orfX
,
orfI
,
orfP
,
orfB
, and
orfA
genes, were checked by PCR and direct sequencing for evidence of their presence in the atypical isolates. The
prs-prfA
cluster-
ldh
region of the
L. seeligeri
isolates was approximately threefold shorter due to the loss of
orfD
,
prfA
,
orfE
,
plcA
,
hly
,
orfK
,
mpl
,
actA
,
dplcB
,
plcB
,
orfH
,
orfX
, and
orfI
. The genetic map order of the cluster genes of all the atypical
L. seeligeri
isolates was
prs-orfA2-orfP-orfB-orfA-ldh
, which was comparable to the similar region in
L. welshimeri
, with the exception of the presence of
orfA2
. DNA sequencing and phylogenetic analysis of 17 housekeeping genes indicated an
L. seeligeri
genomic background in all seven of the atypical
hly
-negative
L. seeligeri
isolates. Thus, the novel biotype of Xyl
+
Rha
−
Hly
−
L. seeligeri
strains can only be distinguished from Xyl
+
Rha
−
L. welshimeri
strains genotypically, not phenotypically. In contrast, the Rha
+
Xyl
+
biotype of
L. welshimeri
would not present an identification issue.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
15 articles.
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