Affiliation:
1. Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA
Abstract
ABSTRACT
Listeria monocytogenes
is a foodborne pathogen that can cause severe disease (listeriosis) in susceptible individuals. It is ubiquitous in the environment and often exhibits resistance to heavy metals. One of the determinants that enables
Listeria
to tolerate exposure to cadmium is the
cadAC
efflux system, with CadA being a P-type ATPase. Three different
cadA
genes (designated
cadA1
to
cadA3
) were previously characterized in
L. monocytogenes
. A novel putative cadmium resistance gene (
cadA4
) was recently identified through whole-genome sequencing, but experimental confirmation for its involvement in cadmium resistance is lacking. In this study, we characterized
cadA4
in
L. monocytogenes
strain F8027, a cadmium-resistant strain of serotype 4b. By screening a mariner-based transposon library of this strain, we identified a mutant with reduced tolerance to cadmium and that harbored a single transposon insertion in
cadA4
. The tolerance to cadmium was restored by genetic complementation with the cadmium resistance cassette (
cadA4C
), and enhanced cadmium tolerance was conferred to two unrelated cadmium-sensitive strains via heterologous complementation with
cadA4C
. Cadmium exposure induced
cadA4
expression, even at noninhibitory levels. Virulence assessments in the
Galleria mellonella
model suggested that a functional
cadA4
suppressed virulence, potentially promoting commensal colonization of the insect larvae. Biofilm assays suggested that
cadA4
inactivation reduced biofilm formation. These data not only confirm
cadA4
as a novel cadmium resistance determinant in
L. monocytogenes
but also provide evidence for roles in virulence and biofilm formation.
IMPORTANCE
Listeria monocytogenes
is an intracellular foodborne pathogen causing the disease listeriosis, which is responsible for numerous hospitalizations and deaths every year. Among the adaptations that enable the survival of
Listeria
in the environment are the abilities to persist in biofilms, grow in the cold, and tolerate toxic compounds, such as heavy metals. Here, we characterized a novel determinant that was recently identified on a larger mobile genetic island through whole-genome sequencing. This gene (
cadA4
) was found to be responsible for cadmium detoxification and to be a divergent member of the Cad family of cadmium efflux pumps. Virulence assessments in a
Galleria mellonella
model suggested that
cadA4
may suppress virulence. Additionally,
cadA4
may be involved in the ability of
Listeria
to form biofilms. Beyond the role in cadmium detoxification, the involvement of
cadA4
in other cellular functions potentially explains its retention and wide distribution in
L. monocytogenes
.
Funder
USDA | National Institute of Food and Agriculture
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
39 articles.
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