Salmonella Typhimurium internalization is variable in leafy vegetables and fresh herbs.
Despite washing and decontamination, outbreaks linked to consumption of fresh or minimally-processed leafy greens have been increasingly reported in recent years. In order to assure the safety of produce it is necessary to gain knowledge regarding the exact routes of contamination. Leaf internalization through stomata was previously reported as a potential route of contamination, which renders food-borne pathogens protected from washing and disinfection by sanitizers. In the present study we have examined the incidence (percentage of microscopic fields harboring ≥ 1 GFP-tagged bacteria) of Salmonella Typhimurium on the surface and underneath the epidermis in detached leaves of seven vegetables and fresh herbs. The incidence of internalized Salmonella varied considerably among the different plants. The highest incidence was observed in iceberg lettuce (81 ± 16%) and arugula leaves (88 ± 16%), while romaine (16 ± 16%) and red-lettuce (20 ± 15%), showed significantly lower incidence (P < 0.05). Internalization incidence in fresh basil was 46 ± 12%, while parsley and tomato leaves demonstrated only marginal internalization (1.9 ± 3.3% and 0.56 ± 1.36%, respectively). Internalization of Salmonella in iceberg lettuce largely varied (0-100%) through a 2 year survey, with a higher incidence occurring mainly in the summer. These results imply that Salmonella internalization occurs in several leafy vegetables and fresh herbs, other than iceberg lettuce, yet the level of internalization largely varies among plants and within the same crop. Since internalized bacteria may evade disinfection, it is of great interest to identify plants which are more susceptible to bacterial internalization, as well as plant and environmental factors that affect internalization.
Microbial Food-Safety Research Unit, Department of Food Quality & Safety, Institute for Postharvest and Food Sciences, Agricultural Research Organization, The Volcani Center, POB 6, Beth-Dagan 50250, Israel.
Dana
D
Golberg
Yulia
Y
Kroupitski
Eduard
E
Belausov
Riky
R
Pinto
Shlomo
S
Sela
D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004203:Disinfection / Q000379:methods; D005506:Food Contamination; D018545:Lactuca / Q000382:microbiology; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D019441:Plant Epidermis / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000302:isolation & purification*; D012621:Seasons; D014675:Vegetables / Q000382:microbiology*