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Title: RESPONSE TO TRISODIUM PHOSPHATE TREATMENT OF SALMONELLA CHESTER ATTACHED TO FRESH-CUT GREEN PEPPER SLICES

Author
item Liao, Ching Hsing
item Cooke, Peter

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2000
Publication Date: 12/7/2000
Citation: Liao, C., Cooke, P.H. 2001. Response to trisodium phosphate treatment of salmonella chester attached to fresh-cut green pepper slices. Canadian Journal of Microbiology. V. 47:25-32.

Interpretive Summary: The incidence of human illness associated with the consumption of fresh fruits and vegetables has increased very dramatically during the past ten years. Disease-causing bacteria such as E. coli and Salmonella have been implicated as the cause of several large and well publicized outbreaks related to the eating of raw or minimally processed produce. Very little is sknown about the sources and routes by which fruits and vegetables become contaminated. The authors demonstrated that Salmonella, when exposed to fresh-cut green pepper slices, attached to the pepper slice almost instantly. Approximately 30% of the bacteria remaining on the slices were firmly attached and could not be removed by repeated washes with agitation. Attached bacteria were located mainly at the surfaces of injured tissues but in much smaller numbers on the unbroken skin. When pepper disks containing attached Salmonella were treated with a commercial disinfectant, ,a small portion of attached bacteria was resistant to or was protected from the disinfectant treatment. A better understanding of the mechanism by which attached bacteria become resistant to the disinfectant treatment would lead to the development of more effective methods for eliminating bacteria from contaminated fruits. Preventing mechanical injury of fresh fruits during and after harvest could also reduce the chance of bacterial attachment and contamination.

Technical Abstract: A laboratory model using green disks to investigate the attachment of Salmonella chester on plant tissue was described. Pepper disks were immersed in a bacterial suspension for 30 seconds and subsequently air-dried at room temperature for 10 min. Approximately 30% of the bacteria retained on the disk after immersion were firmly attached and could not be removed by two washes and agitation. A positive correlation was observed between the number of bacteria attached and the concentration of bacteria in the suspension. Population studies and scanning electron microscopic examinations revealed that attachment of S. chester on pepper disks occurred mainly on the surfaces of injured tissue but rarely on the unbroken skin. When inoculated disks were treated with 3 to 12 % of trisodium phosphate (TSP) at pH 12.3 for 5 min, the population of bacteria on the disk was reduced by 10- to 100-fold. A small portion (0.7 to 7.1 %) )of bacteria attached to the disk was either resistant to or protected from the TSP treatment. When the pH of TSP solution was reduced from 12.3 to 4.5, the effectiveness of TSP in inactivating S. chester on pepper disks was reduced by 26 %. This study shows that surfaces of injured tissue are the principal sites for bacterial attachment . Avoiding mechanical injuries of fresh fruits during and after harvest would reduce the chance of pathogen contamination and improve the effectiveness of sanitizer treatment.