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Cilantro Cilantro (Coriandrum sativuum) is one of the most widely used fresh herbs. It is featured in the cuisines of China, Southeast Asia, India, and Central and South America. It is commonly found in salsas and in poultry and seafood dishes. It is also known as coriander and Chinese parsley(Potter 1996). In March of 1999 an outbreak of Salmonella Thompson occurred. Illness was associated with eating fresh uncooked cilantro or eating a salsa containing fresh cilantro. No farm investigations were carried out due to the lack of records. It was impossible to determine if there was a common grower who supplied the restaurants involved in the outbreak.All restaurants reported washing and chopping the cilantro. Whole and chopped cilantro and the salsa were stored under refrigerated conditions.Campbell and others (2001) examined the ability of Salmonella to survive on cilantro and in fresh salsa containing cilantro. At room temperature a log increase was observed in the Salmonella population on cilantro. A 3-order-of-magnitude increase was observed on chopped cilantro. The organisms grew faster on chopped cilantro due to the release of nutrients from broken plant tissue. Refrigeration can impede the growth of Salmonella on cilantro for 3 days and in fresh salsa for 1 day. Even though salsa has a low pH it will support the growth of Salmonella. A 300-fold increase was observed in the Salmonella population of salsa stored at room temperature after 1 day(Campbell and others 2001). Brandl and Mandrell (2002) examined the ability of Salmonella serovar Thompson to survive on cilantro plants. On cilantro Salmonella grew rapidly at elevated temperatures.Populations of Pantoea agglomerans and Pseudomonas cbloroaphis,organisms that are commonly found on the surface of plants, were 10 times greater than that of Salmonella serovar Thompson on cilantro plants incubated at 22C. At 30C Salmonella serovar Thompson reached significantly higher populations and represented a greater portion of the total portion of microorganisms on the surface of the cilantro. Higher temperature conditions may have allowed Salmonella serovar Thompson to utilize a greater share of the available nutrients, therefore increasing the competitive fitness of the organism. Salmonella serovar Thompson may not have achieved populations as high as the other organisms, because it may be unable to use the wide variety of nutrients on the surface of the cilantro leaf. This organism may be better adapted to metabolize carbon and nitrogen found in the human gut. Salmonella serovar Thompson was able to survive in dry conditions such as 60 or 50% relative humidity for several days and was able to grow to maximal levels when high humidity conditions were restored. Several serovars of Salmonella including S. enterica serovar Derby, S. enterica serovar Newport, S. enterica serovar Enteritidis, and S. enterica serovar Thompson exhibited similar colonization trends on cilantro. Cilantro plants were inoculated with a GFP Salmonella serovar Thompson and observed using confocal laser scanning microscopy. The organisms were observed on leaf veins and adjacent areas as well as the base of the leaf where the petiole joins the leaf. This may be attributed to the waxy trichnome of the cllantro leaf surface as well as the tendency of surface water to accumulate in the depressions of leaf veins. When the GFP Salmonella together with a DsRed P. agglomerans were used to inoculate the surface of cilantro leaves the organisms were detected in large mixed aggregates. Salmonella also formed mixed colonies with the native microflora. Salmonella serovar Thompson was found to infect damaged tissue and reach higher cell densities than on healthy cilantro tissue. Lesions may provide access to the nutritious inner leaf tissue as well as protection from environmental stresses. This clearly demonstrates that human pathogens can colonize plants in the field prior to harvest (Brandl and Mandrell 2002). In a survey of domestic fresh produce conducted by the FDA 1 of 62 cilantro samples tested was contaminated with Sbigella (FDA 2001). One of the cilantro samples was also contaminated with Salmonella. [ Last edited by telomerase on 2009-1-9 at 12:28 ] |
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