title: Novel Cadmium Resistance Determinant in Listeria monocytogenes.
abstract: Listeria monocytogenesis 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 enablesListeriato tolerate exposure to cadmium is thecadACefflux system, with CadA being a P-type ATPase. Three differentcadAgenes (designatedcadA1tocadA3) were previously characterized inL. monocytogenesA 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 characterizedcadA4inL. monocytogenesstrain 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 incadA4The 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 withcadA4CCadmium exposure inducedcadA4expression, even at noninhibitory levels. Virulence assessments in theGalleria mellonellamodel suggested that a functionalcadA4suppressed virulence, potentially promoting commensal colonization of the insect larvae. Biofilm assays suggested thatcadA4inactivation reduced biofilm formation. These data not only confirmcadA4as a novel cadmium resistance determinant inL. monocytogenesbut also provide evidence for roles in virulence and biofilm formation.IMPORTANCEListeria monocytogenesis 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 ofListeriain 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 aGalleria mellonellamodel suggested thatcadA4may suppress virulence. Additionally,cadA4may be involved in the ability ofListeriato form biofilms. Beyond the role in cadmium detoxification, the involvement ofcadA4in other cellular functions potentially explains its retention and wide distribution inL. monocytogenes.
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Cameron
authors.initials: C
authors.lastname: Parsons
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Sangmi
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Victor
authors.initials: V
authors.lastname: Jayeola
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA sophia_kathariou@ncsu.edu.
authors.forename: Sophia
authors.initials: S
authors.lastname: Kathariou
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development; D002104:Cadmium / Q000633:toxicity*; D004251:DNA Transposable Elements / Q000235:genetics; D004195:Disease Models, Animal; D024881:Drug Resistance, Bacterial; D005516:Food Microbiology; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D007814:Larva / Q000382:microbiology; D007915:Lepidoptera / Q000382:microbiology; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D008088:Listeriosis / Q000382:microbiology; D019216:Metals, Heavy; D008826:Microbial Sensitivity Tests; D016297:Mutagenesis, Site-Directed; D016415:Sequence Alignment; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D019216:Metals, Heavy; D002104:Cadmium
keywords: Listeria monocytogenes; biofilm; cadA; cadmium resistance; virulence