Elucidating Escherichia Coli O157:H7 Colonization and Internalization in Cucumbers Using an Inverted Fluorescence Microscope and Hyperspectral Microscopy

Antibacterial mechanism of lysine against Escherichia coli O157:H7, its action on lettuce and in reducing the severity of murine colitis

The aim of the present study was to evaluate the mechanism of antimicrobial action of Lysine (Lys) against Escherichia coli (E. coli) O157:H7. Lys alters the permeability and morphology of bacterial cell membranes, leading to leakage of intracellular material. Using agarose gel electrophoresis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE), it was found that high concentrations of Lys disrupted the DNA and protein primary structure of E. coli O157:H7. Lys also inhibited the ability of E. coli biofilm formation in a concentration-dependent manner. Subinhibitory concentration of Lys reduces the swimming and swarming ability of E. coli O157:H7 and its ability to adhere and to invade Caco-2 cells. The use of Lys on lettuce inoculated with E. coli O157:H7 showed good disinfection efficiency. Further studies revealed that Lys had both preventive and therapeutic effects on the severity of colitis induced by E. coli O157:H7 infected mice, and that the preventive effect was greater than the therapeutic effect.

Colonization of Raphanus sativus by human pathogenic microorganisms

Contamination of vegetables with human pathogenic microorganisms (HPMOs) is considered one of the most important problems in the food industry, as current nutritional guidelines include increased consumption of raw or minimally processed organic vegetables due to healthy lifestyle promotion. Vegetables are known to be potential vehicles for HPMOs and sources of disease outbreaks. In this study, we tested the susceptibility of radish (Raphanus sativus) to colonization by different HPMOs, including Escherichia coli PCM 2561, Salmonella enterica subsp. enterica PCM 2565, Listeria monocytogenes PCM 2191 and Bacillus cereus PCM 1948. We hypothesized that host plant roots containing bactericidal compounds are less prone to HPMO colonization than shoots and leaves. We also determined the effect of selected pathogens on radish growth to check host plant-microbe interactions. We found that one-week-old radish is susceptible to colonization by selected HPMOs, as the presence of the tested HPMOs was demonstrated in all organs of R. sativus. The differences were noticed 2 weeks after inoculation because B. cereus was most abundant in roots (log10 CFU - 2.54), S. enterica was observed exclusively in stems (log10 CFU - 3.15), and L. monocytogenes and E. coli were most abundant in leaves (log10 CFU - 4.80 and 3.23, respectively). The results suggest that E. coli and L. monocytogenes show a higher ability to colonize and move across the plant than B. cereus and S. enterica. Based on fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) approach HPMOs were detected in extracellular matrix and in some individual cells of all analyzed organs. The presence of pathogens adversely affected the growth parameters of one-week-old R. sativus, especially leaf and stem fresh weight (decreased by 47-66 and 17-57%, respectively). In two-week-old plants, no reduction in plant biomass development was noted. This observation may result from plant adaptation to biotic stress caused by the presence of HPMOs, but confirmation of this assumption is needed. Among the investigated HPMOs, L. monocytogenes turned out to be the pathogen that most intensively colonized the aboveground part of R. sativus and at the same time negatively affected the largest number of radish growth parameters.

Infection behavior of Listeria monocytogenes on iceberg lettuce (Lactuca sativa var. capitata)

Iceberg lettuce among leafy vegetables is susceptible to contamination with foodborne pathogens, posing a risk of food microbial safety. Listeria monocytogenes (L. monocytogenes) is a highly lethal pathogen that can survive and proliferate on leafy vegetables. In this paper, the contamination stage, attachment site, internalization pathway, proliferation process, extracellular substance secretion and virulence factors expression of L. monocytogenes on iceberg lettuce were researched. Results showed that the contamination stage of L. monocytogenes on iceberg lettuce was 0-20 min, the proliferation stage was after 20 min. The attachment tissues were stomata and winkles. The internalization distance of L. monocytogenes in the midrib was farther than that in the leaf blade. They enhanced the movement ability of cells by up-regulating the expression of flaA and motA genes, and enhanced the adhesion ability of cells by up-regulating the expression of actA and inla genes, which was beneficial to the proliferation. During proliferation, cells gradually secreted extracellular substances to promote the biofilm formation on iceberg lettuce. The formation of biofilms experienced: individual bacteria, cell aggregation and biofilm maturation. Biofilms were more likely to form on the leaf blade of iceberg lettuce.

Research advances on the contamination of vegetables by Enterohemorrhagic Escherichia coli: pathways, processes and interaction

Enterohemorrhagic Escherichia coli is considered one of the primary bacterial pathogens that cause foodborne diseases because it can survive in meat, vegetables and so on. Understanding of the effect of vegetable characteristics on the adhesion and proliferation process of EHEC is necessary to develop control measures. In this review, the amount and methods of adhesion, the internalization pathway and proliferation process of EHEC have been described during the vegetable contamination. Types, cultivars, tissue characteristics, leaf age, and damage degree can affect EHEC adhesion on vegetables. EHEC cells contaminate the root surface of vegetables through soil and further internalize. It can also contaminate the stem scar tissue of vegetables by rain or irrigation water and internalize the vertical axis, as well as the stomata, necrotic lesions and damaged tissues of vegetable leaves. After EHEC adhered to the vegetables, they may further proliferate and form biofilms. Leaf and fruit tissues were more sensitive to biofilm formation, and shedding rate of biofilms on epidermis tissue was faster. Insights into the mechanisms of vegetable contamination by EHEC, including the role of exopolysaccharides and proteins responsible for movement, adhesion and oxidative stress response could reveal the molecular mechanism by which EHEC contaminates vegetables.

Inhibitory effect of modified atmosphere packaging on Escherichia coli O157:H7 in fresh-cut cucumbers (Cucumis sativus L.) and effectively maintain quality during storage

Modified atmosphere packaging (MAP) can inhibit microbial growth and prolong shelf life of fresh-cut cucumbers. This study compared the effects of different packaging gases on the growth of E. coli O157:H7 and sensory characteristics of fresh-cut cucumbers. Changes in key movement, adhesion, and oxidative stress genes expression of strain under optimal MAP and air were determined. Cell population density, the extracellular carbohydrate complex content and expression of curli fimbriae were evaluated. Results revealed that the growth of E. coli O157:H7 in fresh-cut cucumbers could be effectively inhibited under MAP (atmosphere = 2% O₂, 7% CO₂, 91% N₂), and better maintained the sensory characteristics. Furthermore, the inhibition mechanism was revealed by inhibiting the expression of movement (fliC), adhesion (eaeA) and oxidative stress (rpoS and sodB) genes in E. coli O157:H7, reducing biofilm formation, extracellular carbohydrate production and curli fimbriae expression. Proper MAP can maintain the quality and safety of fresh-cut cucumbers.

Monitoring of transfer and internalization of Escherichia coli from inoculated knives to fresh cut cucumbers (Cucumis sativus L.) using bioluminescence imaging

Slicing may cause the risk of cross-contamination in cucumber. In this study, knife inoculated with Escherichia coli (E. coli) was used to cut cucumbers, bioluminescence imaging (BLI) was used to visualize the possible distribution and internalization of E. coli during cutting and storage. Results showed that the initial two slices resulted in greater bacterial transfer. The bacterial transfer exhibited a fluctuating decay trend, E. coli was most distributed at the initial cutting site. The contaminated area on the surface of cucumber slices decreased during the storage period, which can be attributed to the death and internalization of E. coli. The maximum internalization distance of E. coli was about 2–3 mm, and did not further spread after 30 min from inoculation. Hence, our results provide useful information for risk management in both home and industrial environment.