Bacterial colonization and biofilm development on minimally processed vegetables

Abstract

Bacterial biofilms have been observed and reported on food and food-processing surfaces and can contribute to increased risks for product quality and food safety. The colonization of fruit and vegetables by pectynolitic bacteria like Pseudonomas fluorescens attributable to conditions such as soft rot, can also manifest as biofilms. A developed biofilm structure can provide a protective environment for pathogens such as Listeria monocytogenes reducing the effectiveness of sanitisers and other inhibitory agents. Understanding the colonization of bacteria on leaf surfaces is essential to the development of a better understanding of the leaf ecology of vegetable products. Studies of microbial colonization of leaf surfaces have been conducted using SEM and more recently using confocal microsocpy techniques. In the current study, a Leica TCS NT laser scanning confocal microscope was used to investigate biofilm formation using vital fluorescence staining on intact vegetable leaves. Reflection contrast and fluorescence three-dimensional imaging successfully delineated bacterial and biofilm morphology without disturbing the bacterial or leaf surface structure. The results demonstrate the presence and development of biofilm on the surface of lettuce. The biofilms appeared to originate on the cuticle in distinct micro-environments such as in the natural depression of the stomata, or in the intercellular junction. Bacteria also adhered to and developed biofilm colonies within an hour of contact 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 facilitate the development of improved preservation, sanitising and packaging strategies for minimally processed vegetable products.

Organic acid based sanitizers and free chlorine to improve the microbial quality and shelf-life of sugar snaps

“…the maturity of the sugar snaps and the integrity of the pod at the calyx end, were more that colonize plant surfaces adhere preferentially in the natural depression of stomata or in the intercellular junction, or cracks or crevices formed through damage, after which diverse biofilms can arise, composed of gram-negative and gram-positive bacteria, yeasts and filamentous fungi (Carmichael et al, 1999). The weakening natural defense mechanisms of overmature or mechanically damaged sugar snaps and the loss of structural integrity at the calyx ends, potentially leading to increased solute leakage, improves the growth conditions of phytopathogens (Elghaouth et al, 1992;Nunes et al, 2010).…”

Colonization of Arabidopsis thaliana with Salmonella enterica and Enterohemorrhagic Escherichia coli O157:H7 and Competition by Enterobacter asburiae

“…The source of contamination likely occurs postharvest from a variety of animal sources, including humans (58) Alternatively, preharvest contamination could occur via manure application, contaminated irrigation water, animals, or use of contaminated seed. Whether the contamination originates pre-or postharvest, it has been well documented that S. enterica and E. coli O157:H7 survive and grow on fresh produce (8,11,21,62), especially on sprouts, where the contamination can exceed 10 7 CFU per g of fresh weight (12,57).…”

Biofilm Formation by Escherichia coli O157:H7 on Stainless Steel: Effect of Exopolysaccharide and Curli Production on Its Resistance to Chlorine

“…Attachment and biofilm formation by food-borne pathogens and spoilage microorganisms on food contact surfaces in processing plants are a public health and cross-contamination concern. Biofilms can also form on the surfaces of containers used for harvesting, transporting, and displaying foods at the retail level (4,6,11,21) and can develop on food surfaces (8,9,17). E. coli O157:H7 can form biofilms on stainless steel (14,44,45), and sloughing of cells may result in cross-contamination of foods during processing (20,28,29,34).…”