2012 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.
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 development of table salt-free fermentations demands the use of a bacterial starter culture to assure a rapid initiation of the process. The design of an appropriate fermentation starter culture requires an understanding of the susceptibility of a number of bacterial strains naturally present in the commercial fermentations to bacteriophages or viruses capable of attacking bacteria. Initial efforts have been geared to identify fermentative bacterial strains resistant to the viruses naturally present in the commercial fermentations. A significant number of bacteriophages present in a cucumber commercial fermentation during the most active period when the bacteria reach maximum numbers were identified. 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 bacteria such as Weisella paramesenteroides, Weisella cibaria, Lactobacillus brevis, and Lactobacillus plantarum.
More recently, a survey of bacteriophages able to attack enterobacteria naturally present in the early stage of the commercial fermentation was completed. Enterobacteria can be found on vegetables but are absent in the later stage of the fermented derivative, presumably due to the addition of salt to the fermentation and acids produced. With the development of a table salt-free fermentation the proliferation and survival of such bacteria may become problematic. Bacteriophages may be used as a control agent against the enterobacteria naturally present on fresh vegetables and possibly in the early stage of vegetable fermentations. Twenty six independent enterobacterial bacteriophages were isolated from days 1 and 3 of the fermentation and six of the bacteriophages characterized belong to the Myoviridae, Siphoviridae or Podoviridae families. No enterobacterial phages were isolated in the late stage of the fermentation. Susceptible bacteria included members of the Enterobacter, Cronobacter, and Escherichia genuses. Further studies are needed to test the possibility of using the isolated viruses in the control of the enterobacterial population in commercial table salt-free fermentations.