Listeria seeligeri isolates from food processing environments form two phylogenetic lineages

Abstract

Seven different actA subtypes forming two phylogenetic lineages could be distinguished by sequencing the actA gene of Listeria seeligeri isolates from different habitats. Isolates of the two lineages differ in hemolytic as well as phospholipase activities and in the arrangement of the virulence gene cluster. The presence of a serine protease gene resembling orf2110 of L. monocytogenes in some isolates further supports the hypothesis that L. seeligeri is subject to ongoing adaptation to changing environments.

FIG. 1.

Hypothetical protein sequences of the seven identified ActA subtypes of L. seeligeri (Ls). The protein sequences correspond to the hypothetical translation products of the 253-bp actA gene fragments (Fig. 2). For every subtype, an example is given. Alignments were done with the program BioEdit. The asterisk within the type 4 sequence denominates a stop codon. Gaps are indicated by the “∼” symbol.

FIG. 2.

Dendrogram showing phylogenetic relationship among L. seeligeri (Ls) isolates based on partial actA sequences (253 bp) from L. seeligeri isolates obtained in Upper Franconia, Germany, and reference strains L. seeligeri ATCC 35967 (AY878348) and L. seeligeri NRRL (AY510074). The tree was constructed by the minimum evolution method in the MEGA version 4 package. The bootstrap values presented at corresponding branches were evaluated from 1,000 replications. The phylogenetic lineages of the strains are symbolized with Roman numerals and the corresponding actA subtypes with Arabic numerals. The bar indicates 1.0% sequence divergence. Strains marked with an asterisk carried a gene similar to the orf2110 gene of L. monocytogenes F2365 (AE017262).

FIG. 3.

Phosphatidylinositol-specific phospholipase activity on ALOA agar plates (Merck, Darmstadt, Germany). For analysis of the phospholipase activity, 10 μl of a overnight culture in brain heart infusion (BHI) liquid medium of L. monocytogenes 1 (A), L. seeligeri 90 (B), and L. seeligeri 187 (C) was dropped onto ALOA agar plates and incubated at 37°C for 48 h.