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Title: RADIATION SENSITIVITY AND RECOVERABILITY OF LISTERIA MONOCYTOGENES AND SALMONELLA ON FOUR LETTUCE TYPES

Author
item Niemira, Brendan

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2003
Publication Date: 8/29/2003
Citation: NIEMIRA, B.A. RADIATION SENSITIVITY AND RECOVERABILITY OF LISTERIA MONOCYTOGENES AND SALMONELLA ON FOUR LETTUCE TYPES. JOURNAL OF FOOD SCIENCE. 2003. V. 68 (9). P. 2784-2787.

Interpretive Summary: Lettuce can be contaminated with harmful bacteria such as Listeria monocytogenes (L. mono) and Salmonella. Ionizing radiation can effectively eliminate these pathogens from foods. Outbreak strains of L. mono. or Salmonella were inoculated onto cut leaf pieces of four closely related but structurally distinct types of lettuce: Boston (butterhead lettuce), Iceberg (crisphead lettuce), Green leaf and Red leaf (colored variants of looseleaf lettuce). Samples were gamma-irradiated and the radiation sensitivity of the inoculated bacteria determined. Recovery of bacteria from nonirradiated leaf pieces was also measured. While the radiation sensitivity of L. mono. was not influenced by the associated lettuce type, Salmonella was significantly less sensitive on Green leaf lettuce than on Boston, Iceberg or Red leaf lettuces. For each pathogen, the recoverability from inoculated leaf pieces was significantly different among the four lettuce types. The pattern of recovery of L. mono. was distinct from that of Salmonella. Recovery was apparently related to the complexity of the leaf surface topology. These data show that while irradiation effectively reduced pathogen populations on inoculated lettuce, relatively subtle differences between lettuce types can significantly influence the radiation sensitivity of some associated pathogenic bacteria.

Technical Abstract: Outbreak strain cocktails of Listeria monocytogenes (L. mono) or Salmonella were inoculated onto cut leaf pieces of closely related but structurally distinct types of lettuce (Lactuca sativa): Boston (butterhead lettuce), Iceberg (crisphead lettuce), Green leaf and Red leaf (colored variants of looseleaf lettuce). Samples were gamma-irradiated and the radiation sensitivity of the inoculated bacteria and expressed as a D10-value (the amount of ionizing radiation necessary to reduce the bacterial population by 90%, in kGy). Recovery of bacteria from nonirradiated leaf pieces was also measured. While the radiation sensitivity of L. mono. was not influenced by the associated lettuce type (D10 = 0.19-0.20 kGy), Salmonella was significantly less sensitive on Green leaf lettuce (0.31 kGy) than on Boston (0.24 kGy), Iceberg (0.25 kGy) or Red leaf (0.23 kGy) lettuces. For each pathogen, the recoverability of cfu from inoculated leaf pieces was significantly different among the four lettuce types; the pattern of recovery of L. mono. was distinct from that of Salmonella. Recovery was apparently related to the complexity of the leaf surface topology. These data show that while irradiation effectively reduced pathogen populations on inoculated lettuce, relatively subtle differences between lettuce types can significantly influence the radiation sensitivity of some associated pathogenic bacteria.