Location: Food Science Research2013 Annual Report
1a. Objectives (from AD-416):
To isolate the predominant bacteria present in commercial cucumber fermentations and evaluate their ability to serve as host for bacteriophages possibly present in the same environment.
1b. Approach (from AD-416):
Brine samples of at least two commercial cucumber fermentations will be collected. Samples will be spiral plated on MRS and VRBG agars to select for lactic acid bacteria and enterobacteriaceae. Selected colonies will be isolated and screened for their sensitivity to bacteriophages present in the brine samples. Bacterial hosts and bacteriophages will be identified by 16S rRNA sequencing and electronic microscopy, respectively.
3. Progress Report:
This project is related to in-house objective 1 addressing the development of approaches for commercial cucumber fermentations without the use of sodium chloride that will prevent development of post fermentation microbiological spoilage and retain the quality of cucumbers during storage. The inception of salt-free fermentation technology at the commercial scale demands the use of a bacterial starter culture to assure a rapid initiation of the process and the safety of the fermented goods. The design of an appropriate fermentation starter culture is well underway and benefitted from the initial stage of this project to elucidate the susceptibility of a number of the bacterial strains isolated from commercial fermentations to bacteriophages or viruses capable of attacking bacteria. The first stage of the project revealed that a significant number of bacteriophages, present in a commercial cucumber fermentation, reached maximum numbers during the most active fermentation period. Such bacteriophages belong to the Myoviridae or Siphoviridae families, with the exception of one bacteriophage which belongs to the Podoviridae family. Bacterial strains susceptible to the viruses were lactic acid. Recent findings under this project include the isolation of a group of bacteriophages capable of infecting enterobacteria present in the raw cucumbers and detected during the initial stage of the commercial fermentations. A group of 30 bacteriophages was isolated and 6 of them were characterized. Members of the Podoviridae, Myoviridae and Siphoviridae viral families were found. Specific host were identified as Escherichia coli, Citrobacter spp. and Enterobacter spp. The group of partially characterized viruses will be further screened for their potential to serve as tools to prevent the survival of pathogenic E. coli in foods. Progress on this project was accelerated, finishing research activities by the end of September 2012 as opposed to March, 2013. A manuscript was published in 2012 describing the research completed under the first stage of the project. A second manuscript describing the second stage of this research is under preparation.