Stoma (respiration orifice) in an Iceberg lettuce leaf that has been free of bacterial infection. Lettuce and spinach leaves contaminated with bacteria such as toxigenic Escherichia coli have been a health hazard: the bacteria congregate and propagate around and in the stomata, from where they are impossible to wash out. Clean vegetable leaves are characterized by the absence of bacteria around the stomata. Enhanced SEM. Image width: 36.5 micrometers; magnification: 2740x if the image is printed 10 cm wide.