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 proteinor 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.

Co-occurrence of free-living protozoa and foodborne pathogens on dishcloths: Implications for food safety

“…Amoebae were present in all FLP positive dishcloths, whereas ciliates and flagellates never occurred without amoebae. Flagellates were the most abundant group, which is in agreement with the studies of Vaerewijck et al (2011) and Gourabathini et al (2008) of FLP on food. The lowest numbers were counted for ciliates.…”

“…are common and widely distributed terrestrial ciliates (Foissner, 1993) and are also able to form cysts to survive unfavorable conditions such as desiccation (Maeda et al, 2005). Colpoda steinii has also been recovered from spinach (Gourabathini et al, 2008).…”

“…They are also present on food, like vegetables (Gourabathini et al, 2008;Vaerewijck et al, 2011), and in food-related environments, such as broiler houses (Baré et al, 2009Snelling et al, 2005), meatcutting plants (Vaerewijck et al, 2008), and domestic refrigerators (Vaerewijck et al, 2010).…”

“…In addition, they can also act as a protective niche or shelter for bacteria against harsh environmental conditions (Barker and Brown, 1994;King et al, 1988;Snelling et al, 2005), or even as training grounds and evolutionary cribs for foodborne pathogens (Molmeret et al, 2005), enhancing bacterial virulence and mediating bacterial gene transfer. This points toward a role of FLP in the epidemiology of foodborne pathogenic bacteria with significant implications for food safety and public health International Journal of Food Microbiology 191 (2014) [89][90][91][92][93][94][95][96] (Gourabathini et al, 2008;Greub and Raoult, 2004;Thomas et al, 2010;Vaerewijck et al, 2014).…”

Salmonella transcriptional signature in Tetrahymena phagosomes and role of acid tolerance in passage through the protist

“…This is in contrast with L. monocytogenes, which is digested by the protist and detected infrequently in its fecal pellets (Brandl et al, 2005;Gourabathini et al, 2008). In addition, S. Typhimurium does not decrease the viability of Tetrahymena during its intravacuolar passage (Gourabathini et al, 2008).…”