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Intervention Strategies for Escherichia coli O157:H7 and Salmonella in Organic Soil and on Fresh Produce
Nguekam Yossa, Irene Nadine
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Recently, foodborne diseases caused by Escherichia coli O157:H7 and Salmonella have been increasingly associated with the consumption of fresh produce. Consumers' demand for safe, natural products has led to research on natural antimicrobials for effective control of foodborne pathogens on fresh produce, which can be inadvertently contaminated by soil. Therefore, there is a need to control microbial loads in soil to minimize contamination. The objectives of this study were to evaluate the antimicrobial activity of cinnamaldehyde, Ecotrol®, eugenol, Sporan® and acetic acid against E. coli O157:H7 and Salmonella in organic soil, and to evaluate the antimicrobial effects of cinnamaldehyde and Sporan® alone, or in combination with acetic acid against E. coli O157:H7, Salmonella, and the native microflora of iceberg, romaine and spinach leaves. The quality parameters of the treated fresh produce were monitored, whereas the modes of action of cinnamaldehyde and Sporan® were investigated. The results showed that cinnamaldehyde had the highest bactericidal activity against E. coli O157:H7 and Salmonella in organic soil. Increases in oil concentration resulted in further reduction of both microorganisms. Up to 5 and 6 log CFU/g of E. coli O157:H7 and Salmonella, respectively, were reduced with 2% Sporan® and acetic acid after 24 h. Sporan® in combination with acetic acid (1000SV) and 800 ppm cinnamaldehyde-Tween reduced significantly E. coli O157:H7 (~3 log CFU/g) on iceberg and spinach leaves following treatment at day 0. Likewise, 1000SV treatment reduced Salmonella ~ 2.5 log CFU/g at day 0. E. coli O157:H7 and Salmonella populations in treated iceberg, spinach and romaine leaves were reduced during storage at 4°C. The native microflora of untreated and treated spinach and lettuce leaves increased during the storage time. The texture and the color of iceberg, romaine and spinach leaves treated with essential oils were not significantly different from the control lettuce after 14 days. The scanning and transmission electron microscopy of oil-treated bacterial cells indicated possible cell structural damage and leakage of cellular content. This study shows the potential use of essential oils to effectively reduce E. coli O157:H7 and Salmonella populations in soil and on fresh produce without adversely affecting leaf color and texture.