Differences in attachment of Salmonella enterica serovars to cabbage and lettuce leaves

Authors: Patel, Jitu; Sharma, Manan

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2010
Publication Date: 4/30/2010
Citation: Patel, J.R., Sharma, M. 2010. Differences in attachment of Salmonella enterica serovars to cabbage and lettuce leaves. International Journal of Food Microbiology. 139(1-2):41-47.

Interpretive Summary: The first step in the contamination of produce by human pathogens, such as Salmonella, is attachment to plant surfaces. We determined the ability of different Salmonella enterica strains to attach to and colonize intact and cut lettuce and cabbage surfaces. All Salmonella strains attached rapidly on intact and cut leaf surfaces; although they attached preferentially to cut surfaces of all plants. Salmonella strains attached to Romaine lettuce at significantly higher numbers compared with Iceberg lettuce or cabbage. The attachment strength was also higher on Romaine lettuce, followed by Iceberg lettuce and cabbage. Salmonella Tennessee and Salmonella Thompson attached more tenaciously to leaf surfaces than Salmonella Newport, Salmonella Negev, or Salmonella Braenderup. An understanding of the attachment mechanisms of Salmonella to different produce leaves will be useful in developing new intervention strategies to prevent produce outbreaks. This research is of interest to food scientists and the produce industry.

Technical Abstract: This study investigated the ability of five Salmonella enterica serovars to attach to and colonize intact and cut lettuce (Iceberg, Romaine) and cabbage surfaces. Biofilm assay and attachment of Salmonella serovars to intact and cut leaves were determined. Bacterial populations of loosely and strongly attached Salmonella were obtained to calculate the attachment strength (SR). Biofilm formation as determined by microtiter plate assay varied with strain and the growth medium used. Salmonella Tennessee and Salmonella Thompson produced stronger biofilms compared to Salmonella Newport, Salmonella Negev, and Salmonella Braenderup. Biofilm formation was also stronger when Salmonella spp. were grown in diluted TSB (1:10). All Salmonella serovars attached rapidly on intact and cut produce surfaces. Salmonella attached to Romaine lettuce at significantly higher number than those attached to Iceberg lettuce or cabbage. Salmonella attached preferentially to cut surface of all produce; however, the difference between Salmonella populations attached to intact and cut surfaces was similar (P<0.05). Strong biofilm producing S. Tennessee attached to produce surfaces at significantly higher numbers than the populations of S. Negev. Salmonella attachment to both intact and cut produce surfaces increased with time. The attachment strength of Salmonella was significantly lower on cabbage followed by Iceberg and Romaine lettuce. Overall, S. Tennessee displayed more biofilm formation in vitro and attached more strongly to lettuce than other serovars. Cabbage, intact or cut, did not support attachment of Salmonella as well as Romaine lettuce. Understanding the attachment mechanisms of Salmonella to produce may be useful in developing new intervention strategies to prevent produce outbreaks.