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

Liao, Ching-Hsing; Cooke, Peter H
January 2001
Canadian Journal of Microbiology;Jan2001, Vol. 47 Issue 1, p25
Academic Journal
A laboratory model using green pepper disks was developed to investigate the attachment of Salmonella Chester on plant tissue and to evaluate the effectiveness 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 bacterial suspension containing 1.5 × 10[sup 7] cfu·mL[sup -1] of S. Chester for 30 s 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 (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 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 were 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 fruit tissue are the principal sites for bacterial attachment, and a small portion of the bacteria attached to the tissue are resistant to the sanitizer treatment. Avoiding mechanical injuries to fresh fruits during and after harvest would reduce the chance of pathogen attachment and contamination on green pepper and fruits of similar nature.Key words: Salmonella, attachment, detachment, plant tissue, sanitizer treatment.Nous avons développé une modèle de laboratoire en utilisant des disques de poivrons verts afin d'étudier l'adhérence de Salmonella Chester à des tissus végétaux et d'évaluer l'efficacité d'agents aseptisants à inactiver les bactéries fixées aux fruits. Les disques de poivrons (14 mm de diamètre et 3-4 mm d'épaisseur) furent immergés pendant 30 secondes dans une suspension bactérienne renfermant 1.5 × 10[sup 7] UFC·mL[sup -1] de S. Chester et ensuite séchés à l'air à température pièce pendant 10 min. Environ 30% des bactéries maintenues dans le disque après immersion étaient fermement attachées et impossible à enlever après deux lavages et agitation. Une corrélation positive a été observée entre le nombre de bactéries fixées et la concentration de bactéries en suspension. Des études de population et des examens au microscope électronique à balayage ont montré que S. chester adhérait surtout aux surfaces meurtries (coupures) des disques de poivrons, rarement à la peau en bon état. Les disques inoculés furent traités pendant 5 min. avec de 3% à 12% (m/v) de phosphate trisodique (PTS) d'un pH de 12,3. La tailles des populations bactériennes dans ces disques ont diminué d'un facteur de 10 à 100. Une petite fraction (0,7% à 7,1%) des bactéries fixées étaient soit résistantes au traitement par le PTS, soit protégées de ses effets. Lorsque le pH de la solution de PTS fut ramené à 4,5, l'efficacité d'inactivation du PTS diminua de 26%. Cette étude démontre que la surface des tissus meurtris de fruits représente le principal site d'attachement pour les bactéries et confère une résistance au traitement aseptisant. En évitant les meurtrissures mécaniques de fruits frais pendant et après la récolte, il serait possible de réduire les chances d'adhérence de pathogènes et donc la contamination de poivrons verts et d'autres fruits du même genre.Mots clés : Salmonella, adhérence, dissociation, tissus végétaux, traitement aseptisant.[Traduit par la Rédaction]


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