title: Interactions between food-borne pathogens and protozoa isolated from lettuce and spinach.
abstract: The survival of Salmonella enterica was recently shown to increase when the bacteria were sequestered in expelled food vacuoles (vesicles) of Tetrahymena. Because fresh produce is increasingly linked to outbreaks of enteric illness, the present investigation aimed to determine the prevalence of protozoa on spinach and lettuce and to examine their interactions with S. enterica, Escherichia coli O157:H7, and Listeria monocytogenes. Glaucoma sp., Colpoda steinii, and Acanthamoeba palestinensis were cultured from store-bought spinach and lettuce and used in our study. A strain of Tetrahymena pyriformis previously isolated from spinach and a soil-borne Tetrahymena sp. were also used. Washed protozoa were allowed to graze on green fluorescent protein- or red fluorescent protein-labeled enteric pathogens. Significant differences in interactions among the various protist-enteric pathogen combinations were observed. Vesicles were produced by Glaucoma with all of the bacterial strains, although L. monocytogenes resulted in the smallest number per ciliate. Vesicle production was observed also during grazing of Tetrahymena on E. coli O157:H7 and S. enterica but not during grazing on L. monocytogenes, in vitro and on leaves. All vesicles contained intact fluorescing bacteria. In contrast, C. steinii and the amoeba did not produce vesicles from any of the enteric pathogens, nor were pathogens trapped within their cysts. Studies of the fate of E. coli O157:H7 in expelled vesicles revealed that by 4 h after addition of spinach extract, the bacteria multiplied and escaped the vesicles. The presence of protozoa on leafy vegetables and their sequestration of enteric bacteria in vesicles indicate that they may play an important role in the ecology of human pathogens on produce.
authors.affiliation: Center for the Management, Utilization, and Protection of Water Resources, Tennessee Technological University, Cookeville, TN 38505, USA. sberk@tntech.edu
authors.forename: Poornima
authors.initials: P
authors.lastname: Gourabathini
authors.forename: Maria T
authors.initials: MT
authors.lastname: Brandl
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Redding
authors.forename: John H
authors.initials: JH
authors.lastname: Gunderson
authors.forename: Sharon G
authors.initials: SG
authors.lastname: Berk
mesh_terms: D000818:Animals; D002452:Cell Count; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology*; D056890:Eukaryota / Q000254:growth & development / Q000302:isolation & purification / Q000382:microbiology*; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D018545:Lactuca / Q000382:microbiology* / Q000469:parasitology*; D008089:Listeria monocytogenes / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D019779:Salmonella enterica / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology*; D018724:Spinacia oleracea / Q000382:microbiology* / Q000469:parasitology*; D013194:Staining and Labeling; D022161:Transport Vesicles / Q000382:microbiology; D000097573:Red Fluorescent Protein
chemical_list: D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D000097573:Red Fluorescent Protein