Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 24, 2011
Publication Date: July 30, 3011
Citation: Macarisin, D., Bauchan, G.R., Giron, J., Patel, J.R. 3011. Role of curli expression by Escherichia coli O157:H7 on the cell’s ability to attach to spinach. [abstract]. International Association for Food Protection abstract book #P2-80..
Introduction: Shiga-toxigenic Escherichia coli O157:H7 (STEC) outbreaks have been linked to consumption of fresh produce. Mechanisms of bacterial interaction with plant surfaces should be investigated to develop mitigation strategies. Cellular appendages, such as curli fibers have been suggested to be involved in STEC persistence in fresh produce as these curli are critical in biofilm formation and adherence to animal cells.
Purpose: To determine the role of curli in attachment of STEC on spinach in natural production environment and marketplace.
Methods: The curli expression by wild-type STEC strain, EDL933, and deriving curli-deficient (csgA and csgD) and curli-restored (csgA(pCsgA)) mutants grown on TSB agar at 20, 26 and 37ºC was determined by Congo red (CR) binding assay and Scanning Electron Microscopy (SEM). Spinach leaves were spot inoculated with 106 CFU of bacteria/g of leaf and incubated at 12, 26 and 37ºC for 18h. After incubation, leaves were washed three times in PBS and then homogenized by Polytron® to determine populations of strongly attached bacteria. Further, attachment was confirmed by Laser Scanning Confocal Microscopy (LSCM).
Results: STEC 'csgA and 'cgsD mutants didn’t express curli at 20, 26, and 37ºC, whereas EDL933 and csgA(pCsgA) developed a clear red phenotype on CR medium at 20 and 27ºC. At 37 ºC curli expression by EDL933 on CR medium was less pronounced compared to 'csgA(pCsgA). SEM and LSMS analysis confirmed EDL933 and 'csgA(pCsgA) cells expressing extracellular matrix containing curli fibres. When incubated at 12 and 26ºC, 'csgA and 'cgsD attached to spinach leaves at significantly (P=0.01) lower numbers compared to EDL933 and 'csgA(pCsgA). However, attached bacterial populations among strains weren’t significant when leaves were incubated at 37°C
Significance: Understanding the role of curli in STEC attachment and persistence in vegetal matrices will help developing intervention strategies to remove pathogens from fresh produce and thereby reduce future recalls.