Bacterial colonization and biofilm development on minimally processed vegetables

Bacterial biofilms have been observed and reported on food and food-process ing surfaces and can contribute to increased risks for product quality and food safety. The colonization of fruit and vegetables by pectynolitic bacte ria like Pseudomonas fluorescens attributable to conditions such as soft ro t, can also manifest as biofilms. A developed biofilm structure can provide a protective environment for pathogens such as Listeria monocytogenes redu cing the effectiveness of sanitisers and other inhibitory agents. Understan ding the colonization of bacteria on leaf surfaces is essential to the deve lopment of a better understanding of the leaf ecology of vegetable products . Studies of microbial colonization of leaf surfaces have been conducted us ing SEM and more recently using confocal microsocpy techniques. In the curr ent study, a Leica TCS NT laser scanning confocal microscope was used to in vestigate biofilm formation using vital fluorescence staining on intact veg etable leaves. Reflection contrast and fluorescence three-dimensional imagi ng successfully delineated bacterial and biofilm morphology without disturb ing the bacterial or leaf surface structure. The results demonstrate the pr esence and development of biofilm on the surface of lettuce. The biofilms a ppeared to originate on the cuticle in distinct microenvironments such as i n the natural depression of the stomata, or in the intercellular junction. Bacteria also adhered to and developed biofilm colonies within an hour of c ontact and with clean stainless steel surfaces. Our study investigates the progression of biofilm formation from leaf colonization, and will assist in characterising the critical mechanisms of plant/host interaction and facil itate the development of improved preservation, sanitising and packaging st rategies for minimally processed vegetable products.