Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/10/2005
Publication Date: 12/1/2005
Citation: Gilbreth, S.E., Call, J.E., Wallace, F.M., Scott, V., Chen, Y., Luchansky, J.B. 2005. Relatedness of listeria monocytogenes recovered from selected ready-to-eat foods and listeriosis patients in the united states. Applied and Environmental Microbiology. pg. 8115-8122. Interpretive Summary: Listeria monocytogenes is a bacterium frequently found in ready-to-eat (RTE) foods and in the environment that can cause foodborne illness. In collaboration with the Food Products Association, 31,705 RTE foods including luncheon meats, soft/mold-ripened cheese, and seafood salads were sampled for contamination by this bacterium. A total of 502 isolates were recovered from 577 products that tested positive for L. monocytogenes. An additional 42 clinical isolates from human cases of listeriosis were included in the analysis to examine their relatedness to the food isolates. All of the 544 isolates were recovered from Maryland and Northern California in 2000 and 2001. The genetic relatedness of these isolates were examined using pulsed-field gel electrophoresis (PFGE), a technique used to trace outbreaks and contamination routes by the Centers for Disease Control and Prevention. Using this technique the isolates displayed 139 genetic types and associated into 16 groups. However, 50% of the food isolates displayed only 13 of these genetic types. Additionally, there were 13 clinical isolates that displayed a genetic type that was also found in the food isolates. These data indicate that the majority of L. monocytogenes isolates recovered from the RTE foods sampled in the present study belong to relatively few genetic types. These data will help define the genetic types and relatedness of isolates found in RTE foods and those that cause listeriosis.
Technical Abstract: Pulsed-field gel electrophoresis (PFGE) and serotyping were performed on 544 isolates of Listeria monocytogenes: 502 isolates recovered from 577 contaminated products from among 31,705 ready-to-eat food (RTE) retail samples and 42 isolates recovered from human cases of listeriosis. Isolates were from Maryland (294) and California (250) and were collected in 2000 and 2001. The isolates associated into 16 AscI pulsogroups (greater than or equal to 66% relatedness within each group), 139 AscI pulsotypes (percent relatedness ranging from greater than or equal to 25%-100%), and 8 serotypes (1/2a, 1/2b, 1/2c, 3a, 3b, 4b, 4c, and 4d). The most frequently found pulsotypes belonged to either pulsogroup A (150 food plus 4 clinical isolates) or pulsogroup B (104 food plus 5 clinical isolates). The majority of the 502 food isolates were either serotype 1/2a (298 isolates) or 1/2b (133 isolates), whereas the majority of the 42 clinical isolates were either serotype 1/2a (19 isolates) or 4b (15 isolates). Additionally, 13 clinical isolates displayed pulsotypes also found in food isolates, whereas the remaining 29 clinical isolates contributed 24 unique pulsotypes. There was no appreciable difference in the pulsotype or serotype of the isolates based on geography or seasonality. These data indicate that approximately 50% of the L. monocytogenes isolates found among the numerous RTE foods sampled herein displayed thirteen pulsotypes and only two serotypes. These data will help define the distribution and relatedness of isolates found in RTE foods and those that cause listeriosis.