title: Long-term survival of Escherichia coli O157:H7 and Salmonella enterica on butterhead lettuce seeds, and their subsequent survival and growth on the seedlings.
abstract: The long-term survival of enteric pathogens on butterhead lettuce seeds, and their subsequent survival and growth on seedlings were investigated. Lettuce seeds were inoculated at a high level with two Salmonella enterica and two Escherichia coli O157:H7 strains each (±8 log₁₀ CFU/g seed) and the survival of the pathogens was monitored over two years using standard plating techniques on selective medium. The Salmonella strains (serovars Typhimurium and Thompson) survived significantly better on the seeds than the E. coli O157:H7 strains (MB3885 and NCTC12900). When individual seeds were tested two years after inoculation, Salmonella was recovered from each individual seed, whereas E. coli O157:H7 only from 4% to 14% of the seeds, depending on the recovery method. When contaminated stored seeds were germinated and the seedlings examined for presence of the pathogens, it was clear that both pathogens were able to proliferate on the seedlings. Pathogen counts up to 5.92 log₁₀ CFU and 4.41 log₁₀ CFU per positive seedling were observed for Salmonella and E. coli O157:H7, respectively. Our study not only confirms the long-term survival of enteric pathogens on seeds but also shows that the pathogens maintain their ability to resuscitate and proliferate on the seedlings. Seeds or seedlings should be considered as contamination sources for the cultivation of leafy vegetables such as butterhead lettuce grown in greenhouses.
authors: Institute for Agricultural and Fisheries Research-ILVO, Technology and Food Science Unit-Food Safety, Brusselsesteenweg 370, B-9090 Melle, Belgium.
authors: Inge
authors: I
authors: Van der Linden
authors: Bart
authors: B
authors: Cottyn
authors: Mieke
authors: M
authors: Uyttendaele
authors: Geertrui
authors: G
authors: Vlaemynck
authors: Martine
authors: M
authors: Maes
authors: Marc
authors: M
authors: Heyndrickx
mesh_terms: D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000254:growth & development*; D018525:Germination; D018545:Lactuca / Q000382:microbiology*; D050296:Microbial Viability; D018515:Plant Leaves / Q000382:microbiology; D019779:Salmonella enterica / Q000254:growth & development*; D036226:Seedlings / Q000382:microbiology; D012639:Seeds / Q000382:microbiology*; D014675:Vegetables / Q000382:microbiology