ORAL: E. coli O157:H7 and Salmonella attachment and internalization in fresh cut iceberg lettuce packed in modified atmosphere and stored at 7 °C

VAN DER LINDEN I.; AVALOS LLANO, KARINA ROXANA; ERIKSSON M.; DE VOS W.; VAN DAMME E; UYTTENDAELE M.; DEVLIEGHERE F.

Santiago

Congreso; IX Congreso Iberoamericano de Tecnología Postcosecha y Agroexportaciones; 2017

Facultad de Ciencias Agronómicas de la Universidad de Chile. Instituto de Investigaciones Agropecuarias (INIA). Asociación Iberoamericana de Tecnología Postcosecha (AITEP)

The effect of modified atmosphere packaging (MAP) and storage conditions on the attachment and internalization of Escherichia coli O157:H7 and Salmonella enterica in fresh cut iceberg lettuce was studied. Pieces inoculated with green fluorescent protein labeled E. coli O157:H7 BRMS ID 188 or Salmonella Typhimurium were packed under near ambient atmospheric air conditions or equilibrium modified atmosphere with 3% O2, and stored in dark conditions or under light conditions for 2 days at 7 °C. During storage, the pathogen?s capacity to attach to the lettuce surface and cut edge was evaluated with conventional plating technique and internalization was investigated with confocal microscopy. Furthermore, the effect of decontamination (40 ppm NaOCl or 40 ppm peracetic acid + lactic acid) of the lettuce prior to packaging was evaluated as well. Although around 90% of the pathogens could be easily removed from the central part of the lettuce surface by washing, no significant reduction of the bacteria from the cut edges was obtained. Storage time, light or MAP conditions had no significant influence regarding attachment of the pathogens. Analysis by quantitative confocal microscopy showed that the pathogens were present on the lettuce surface and were sometimes found associated with the stomata, but the bacteria did not enter the tissue through the stomata. Moreover, most of the pathogens penetrated the wounded tissue of the cut edge and were situated inside the lettuce tissue, where they were protected against washing. Prior washing with decontamination agents was not more effective than a rinse with precooled tap water. Our results indicate that at 7 °C, storage conditions (atmospheric conditions, time, light) have no substantial influence on the internalization and attachment of Salmonella and E. coli O157:H7 on cut iceberg lettuce. Cut edges of the lettuce are associated with the highest risk for internalization of the pathogens.