Response to trisodium phosphate treatment of Salmonella Chester attached to fresh-cut green pepper slices

A laboratory model using green pepper disks was developed to investigate th e attachment of Salmonella Chester on plant tissue and to evaluate the effe ctiveness of sanitizer agents in inactivating attached bacteria on fruits. Pepper disks (14 mm in diam, and 3-4 mm in thickness) were immersed in a ba cterial suspension containing 1.5 x 10(7) cfu.mL(1) of S. Chester for 30 s and subsequently air- dried at room temperature for 10 min. Approximately 3 0% of the bacteria retained on the disk after immersion were firmly attache d and could not be removed by two washes and agitation. A positive correlat ion was observed between the number of bacteria attached and the concentrat ion 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 (cut) tissue but rarely on the unbroken skin. When inoculated disks were treated with 3% to 12% (w/v) of trisodium phosphate (TSP) at pH 12.3 for 5 min, the population of bacte ria on the disk was reduced by 10- to 100-fold. A small portion (0.7% to 7. 1%) of bacteria attached to the disk were either resistant to or protected from the TSP treatment. When the pH of TSP solution was reduced from 12.3 t o 4.5, the effectiveness of TSP in inactivating S. Chester on pepper disks was reduced by 26%. This study shows that surfaces of injured fruit tissue are the principal sites for bacterial attachment, and a small portion of th e bacteria attached to the tissue are resistant to the sanitizer treatment. Avoiding mechanical injuries to fresh fruits during and after harvest woul d reduce the chance of pathogen attachment and contamination on green peppe r and fruits of similar nature.