Long-term survival of Escherichia coli O157:H7 and Salmonella enterica on butterhead lettuce seeds, and their subsequent survival and growth on the seedlings

• Published in: International journal of food microbiology Vol. 161; no. 3; pp. 214 - 219
• Main Authors: Van der Linden, Inge, Cottyn, Bart, Uyttendaele, Mieke, Vlaemynck, Geertrui, Maes, Martine, Heyndrickx, Marc
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.02.2013; Elsevier
• Subjects: Biological and medical sciences; Colony Count, Microbial; Escherichia coli; Escherichia coli O157 - growth & development; Escherichia coli O157:H7; Food industries; Food microbiology; Food safety; Fundamental and applied biological sciences. Psychology; General aspects; Germination; Hygiene and safety; Lactuca - microbiology; Microbial Viability; Plant Leaves - microbiology; Salmonella; Salmonella enterica; Salmonella enterica - growth & development; Seedlings - microbiology; Seeds; Seeds - microbiology; Sprouting seeds; Vegetables - microbiology; Sprouting seeds; Salmonella; Food safety; Seeds; Escherichia coli O157:H7; Vegetables; Growth; Escherichia coli; Long term; Survival; Seedlings; Lettuce; Bacteria; Enterobacteriaceae
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2012.12.015

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 (±8log10 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 5.92log10 CFU and 4.41log10 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. ► The long-term survival of enteric pathogens on lettuce seeds was studied. ► After two years, their survival and growth on the seedlings were investigated. ► The pathogens maintained their ability to resuscitate and proliferate on the seedlings.